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#437988 - 06/02/12 10:35 pm opinions on recessed or pocketed valve seats?  
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BrizzoBrit Online content
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Hi All,

Coming up to time to do a top end overhaul to freshen up the rings on my '69 A65F. Have had issues with valve spring coil binding in the past and now valve sticking so will fit new valve springs from Ed V and possibly new guides and black diamond valves if the old ones are not right.

I have 2 heads to choose from, the one currently in use on the bike or a spare that I replaced because the seats had been cut a bit deep (by a **** head shop that I wont be using again). My question is: 'does the recessing of the seats REALLY matter?' I'll see if I can get a photo later today. It's probably not too bad. This bike is used as daily rider mostly commuting but would like it to perform as well as it can and to use it for longer faster runs as well. I blended the worst bits a little, but is there REALLY any SIGNIFICANT shrouding and would this matter on a street bike? Does this cause problems with spring setup? See the pic below. Most obvious where I have added the yellow lines. (Bit embarrassing the amount of oil carbon on this but the heads got swapped when I did last ring change)



Also, seems the earlier smaller ported heads have better mid-range. Not sure exactly what heads I have. What is the easiest way to tell the earlier and later heads with different inlet tract sizes apart. Casting numbers? Rear head bolt size (but mine may have been alterd)? I think the one currently in use is a later head, but uncertain. Added at edit: Both heads have 68-701 casting number.

Final question and one that relates to the last question is cleaning up the inlet tract. EdV told me A65 inlets are a bit restricted around the guide area and they can be taken out a bit in this area. My concern is that I dont want to lose any of the low end on this bike as it does get used mostly in traffic. My plan is really to leave the inlet tract alone unless there is really something useful to be gained here. I'm running a megacycle 542-x2 cam (and 930's) which I find has good mid-range, but the x2 cam did lead to loss of some off-the-line driveability. Dont want to exacerbate this. My feeling is pretty much anything I could do would be detrimental rather than helpful. The inlets already seems to have been bored, possibly with no taper. Both heads much the same see pic below. Goal would be to increase gas speed I'm guessing rather than just try to increase overall flow. I'd be prepared to mess around with one of the heads I guess. Not really aiming to diverge from standard just want to optimise what I've got. Definitely not trying to build a race engine or push the useful rev range up higher.

Added at edit: now looking at the dismantled head it clear there is a bit of a bottleneck around the guide. The guy who will be doing my head this time is an experienced motorcycle head specialist I will discuss with him cleaning around this area. Anyone have any input into that?



Thanks in advance
Ray

Last edited by BrizzoBrit; 06/03/12 10:01 am.

BSA 1969 A65F
BSA 1966 A65H
Triumph 1968 T120
Kawasaki A1R
& too many projects!
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#438005 - 06/03/12 12:45 am Re: opinions on recressed or pocketed valve seats? [Re: BrizzoBrit]  
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Rickman Offline
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Ohio
Ray,
I'm working on three A65's right now myself.

I do NOT claim to be terribly knowledgeable.

It is my information, available to me anyways, that any shrouding of the valve is not good... And while the "blending back" of the head material might have helped the gas flow, once you try to replace the seats, unless you reweld the aluminum {?} of the head back up, or unless you replace the seats with larger diameter seats, the stock seats will protrude down out of the head, with the blended area still blended back, won't it?
I think the springs would have more length to go, before coil binding, unless when they checked installed height and reshimmed.... OR the springs were already weak, or collapsed, aaaand reshimmed....

I have one "small valve head". The small valves disappeared into any of the large valve head ports, no contact with the seats.
I ended up replacing all the guides and valves, none of them were useable with any of these heads, all were worn and loose in their guides.

Inlet tract: I personally do NOT like the rather SHARP 90+ degree bend in the inlet, right at the valve pocket.
I took a dremel and fine sand paper to this area, and made it much more rounded, hopeing to make the gas flow path easier.
We will see what happens...
Brett

#438016 - 06/03/12 2:42 am Re: opinions on recressed or pocketed valve seats? [Re: Rickman]  
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Cheers Brett,

Yes, appreciate the problem with blending and then replacing seats. Didnt really have a lot of options at the time. The head guy I have found can do the welding,and new seats but the head with the recessed valves I'm treating as a 'spare' really. At the time it was cheaper to find a replacement head than go the 'repair' option. Not sure that's the case anymore with USPS to Australia getting ridiculous (I saw $44 for a set of (2 stroke) rings on some evilbay sellers this morning!!). Heads in Australia are not that easy to come by at reasonable prices.

People I have approached about seats tend not to like the A65 as the seats are not Concentric with the guides (or so they tell me). In any case I've done about 7-8000 miles on each of the heads I have. Havent pulled the valves yet on the current one, but the exhaust seats on the pictured one were pitted. The inlets were perfect. Not sure whether this will fire up a discussion on the requirement for hardened seats. I try to use lead replacement additive when possible, but dont always. I purposely avoided any talk of seats in my first post as there are strong and diverging opinions on that one and wasnt seeking info on thet (yet shocked ).

Looks like I've got other problems as well, havent pulled the barrels yet but looks like it had been sucking oil from the pushrod tower and a fair old carbon build up in that area on the piston crowns.

Looks like I'm confusing valve size with inlet tract size. Need to go and find some of Rich B's posts but I find the search function to be pretty RS.

Many thanks
Ray


BSA 1969 A65F
BSA 1966 A65H
Triumph 1968 T120
Kawasaki A1R
& too many projects!
#438035 - 06/03/12 4:31 am Re: opinions on recressed or pocketed valve seats? [Re: BrizzoBrit]  
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Rickman Offline
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Ohio
Ray,
It sounds as if you may need to check the flatness of your head and barrel mating surfaces... For the oil consumption...

There were at least 4 A65 heads at Steubenville today... About the only 'common' part available there... Didn't need one, so never asked for any prices...

...I did think you were talking about two different things, re: valves and inlet tract.... I wasn't aware there were more than one inlet tract size...? Except for the single carb heads being different from twin carb heads... True A50 heads being different from True A65 heads... STOCK, and not worked on!
Brett

#438058 - 06/03/12 9:50 am Re: opinions on recressed or pocketed valve seats? [Re: Rickman]  
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BrizzoBrit Online content
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Hi Brett,

Spot on, I will get the head checked and skimmed (as little as possible) if necessary.

Valve size / port size: I was under the impression that somewhere around '65 had smaller ports but with the large valves. Often get confused with these things until I research them in detail.

Used to enjoy the Steubenville swap when I lived in Pittsburgh. I'd like to be able to do the swap meet thing rather than eBay, but there's a small small problem of distance and time. Swaps in Australia stopped being useful for me a long time ago. Havent been to one in years.

Turns out the inner exhaust spring was broken on the timing side exhaust. Another good reason to use decent springs if you can get them. Did have what seemed to be a loss of compression on that side a few days ago. My timing for the rebuild couldnt have been better. I have already got all the parts I should need. I was stuck using these old recycled springs because the replacements I had were coil bound or so close that it didnt matter at full lift. Because I use the bike as my only mode of daily transport I sometimes have to put it back together with what I have. There was also some evidence the followers were bouncing on the closing side of the lobe. So all-in-all the springs were not up to it.

As always, should be better when this is all done. Slowly getting this bike sorted.

Cheers
Ray


BSA 1969 A65F
BSA 1966 A65H
Triumph 1968 T120
Kawasaki A1R
& too many projects!
#438062 - 06/03/12 10:06 am Re: opinions on recressed or pocketed valve seats? [Re: ]  
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BrizzoBrit Online content
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Thanks for the clarification on that one Allan.

Both my heads are the 'big valve' then with casting number 68-701.

Seats were not as nice as the one pictured, but will get all the new bits I have and a 3 angle cut.

Cheers
Ray


BSA 1969 A65F
BSA 1966 A65H
Triumph 1968 T120
Kawasaki A1R
& too many projects!
#438095 - 06/03/12 1:06 pm Re: opinions on recressed or pocketed valve seats? [Re: ]  
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Arnstein Offline
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Arnstein  Offline
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Kristiansund. Norway
The statement that the small valve a65 were the quickest made and that BSA got hooked on big valves and lost power from doing so is very bold.
The thruth is that the fastest (1/4-mile and top speed) std a65`s is the ones with 40.5mm inlet valves and 32mm carbs.

Comparing other engines with the same bore & stroke (75x74mm) I find that for example the Yamaha xs 650 have 41 mm inlet valves and the fastest Laverda 3cyl.triples have 40.5mm and from 32 to 36 mm carbs (36mm:the SFC 1000 which is the fastest). The fastest a65 have 32mm carbs. All of these engines are redlined at approx.7500rpm.


Arnstein

BSA Spitfire MK3.800cc
Honda CB450T -71
Laverda RGS 1130cc -85
Ducati 1098 -08
#438121 - 06/03/12 3:44 pm Re: opinions on recressed or pocketed valve seats? [Re: ]  
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Arnstein Offline
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The road test by Motor cycle of the Spitfire mk2 Motor cycle states :"Here is a model that looks like 120mph and actually does it.That this is by far the the fastest-ever production job from the Small Heath factory is beyond dispute,but it also qualifies as the fastest standard machine tested by Motor Cyle".Highest one-way speed 123mph.
Regarding inlet valves/ports,to compare the short stroke a65 to the long stroke Triumps is wrong I think.As I said: The Laverda triples and the Yamaha xs650 (bore - stroke the same as the a65) is the better comparison with bigger or the same dia . inlets as the a65.
Modern short stroke engines has very big valves considering their displacement,example the Ducati 1098 (which was the strongest twincylinder ever when it was released in 2007) bore & stroke 104x64.7mm with two 42mm inlet valves pr.cylinder and throttle body 60mm.
Do you really think the Ducati will be stronger if the inlets was made smaller like for example a Harley sportster of similar displacement ?


Arnstein

BSA Spitfire MK3.800cc
Honda CB450T -71
Laverda RGS 1130cc -85
Ducati 1098 -08
#438152 - 06/03/12 5:58 pm Re: opinions on recressed or pocketed valve seats? [Re: BrizzoBrit]  
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Arnstein Offline
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The difference xs 650 and a65 regarding the matter we`re talking about here is not so big that it will make much wrong..same with the Laverda,the port shape and valve angle is similar.

When it comes to carbs.,I put on my Spitfire Mikunis(similar as the ones on xs 650) when the Concentrics was worn out for the third time ( I sleeved them) and find there is very little difference,if any at all.)

The Spitfire was useless in town because of the GPs.
When it comes to vibration they vibrates similar as any 360 degree paralell twin without balance weights.

Many of the a65`s regardless of type vibrated badly while others is acceptable.My 800cc Spitfire with dynamically balanced Nourish crank is a quite good and has a lot of torque low down mainly because of the high.comp.(It had 10.5-1 pistons when 650 also) and with standard gearing it`s just as good in town as any other a65.

And as most of us know,there is more to play than just cylinder size and carbs.That goes witout saying.


Arnstein

BSA Spitfire MK3.800cc
Honda CB450T -71
Laverda RGS 1130cc -85
Ducati 1098 -08
#438153 - 06/03/12 6:00 pm Re: opinions on recressed or pocketed valve seats? [Re: BrizzoBrit]  
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Arnstein Offline
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Kristiansund. Norway
The difference xs 650 and a65 regarding the matter we`re talking about here is not so big that it will make much wrong..same with the Laverda,the port shape and valve angle is similar.

When it comes to carbs.,I put on my Spitfire Mikunis(similar as the ones on xs 650) when the Concentrics was worn out for the third time ( I sleeved them) and find there is very little difference,if any at all.)

The Spitfire was useless in town because of the GPs.
When it comes to vibration they vibrates similar as any 360 degree paralell twin without balance weights.

Many of the a65`s regardless of type vibrated badly while others is acceptable.My 800cc Spitfire with dynamically balanced Nourish crank is a quite good and has a lot of torque low down mainly because of the high.comp.(It had 10.5-1 pistons when 650 also) and with standard gearing it`s just as good in town as any other a65.

And as most of us know,there is more to play than just cylinder size and carbs.That goes witout saying.


Arnstein

BSA Spitfire MK3.800cc
Honda CB450T -71
Laverda RGS 1130cc -85
Ducati 1098 -08
#438184 - 06/03/12 9:20 pm Re: opinions on recressed or pocketed valve seats? [Re: BrizzoBrit]  
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Arnstein Offline
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Arnstein  Offline
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Why should a stock Spitfire with Mikunis top only 105mph when they are supposed to be "far superior" (your words)?

My Spitfire had the Mikunis for a while when 650 and my experience is they are similar to concentrics..because the bike behaved similar,also at top speed, (which was quite a bit more than 105mph).
In my experience the Spitfire,because of the high.comp.pistons (which gives good low down torque) and concentrics is very rideable compared to both the Lightning and Thunderbolt.So,what it suffers in torque on low rpm because of the 2mm bigger inlets/carbs it gains because of its h.comp.and it will give the most power throughout the rev.range and of course be the fastest "beyond dispute" as said by Motor cycle.

And I do not compare lobsters to whales,I talk out of experience with my high mileage Spitfire and many other bikes I `ve worked on and owned over the years.

For examle will the change of carbs alone sometimes give big advantages..as when I changed the 36mm Dellortos to Mikuni 36mm flatslides on my 80mm bore Laverda RGS 3cyl. The low/midrange torque became very much better while the top stayed similar. In fact I `m thinking of maybe convert to these carbs on the a65.


Arnstein

BSA Spitfire MK3.800cc
Honda CB450T -71
Laverda RGS 1130cc -85
Ducati 1098 -08
#438190 - 06/03/12 10:06 pm Re: opinions on recressed or pocketed valve seats? [Re: BrizzoBrit]  
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Adam M. Online content
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Allan, did you try 466 head ?
Did any of britbike BSA users use this head and has same experience to share i.e. can compare it to later head ?

Last edited by Adam M.; 06/03/12 10:07 pm.
#438275 - 06/04/12 10:16 am Re: opinions on recressed or pocketed valve seats? [Re: BrizzoBrit]  
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Mark Parker Offline
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Bega NSW Australia
Ray, having new seats fitted is a pretty simple not too expensive excercise if they are deeply recessed. They often get deep with the use of modern valve seat cutting machines that do 3 angles at once. Three angles is definitely the way to go with narrow seats which are not recessed. I do my seats with grinding stones and the seal seems better than any other way, it's just a bit time consuming getting them exactly the width and on the valve where I want. I use the std seats with unleaded 98 and use no additives, the seats do not recess nor give a problem. I use nitrided valves in Kliners and they can run tight clearences without sticking.
I haven't tried it on a head with std valves and std carb sizes but if you alter the shape of the port esp around the turn under the valve guide you should be able to pick up gas speed and flow.
This is with opened up inlet port without any filling in the floor of the port.

This has more or less the same port with a filled floor, its built up under the guide but the port is well opened up, on a std port taking material away from the floor under the guide is likely detrimental, smoothing might be ok so the curve is smooth but not digging it away.

The open port flows a lot of air and makes a motor very powerful in the top end. From what I've read the floor of the port where the JB weld is built up is a dead flow area and possible source of turbulance. What that means is that filling it does not deminish the top end flow and power, however it makes the port smaller and so the gas velocity in the port is raised, so the difference between the two heads is the lower one gives better power from lower RPM and at least as good in the top end. The motor is actually up about 4-5HP with the second style head but as I'd rebuilt the motor that might have been due to something else. What was noticable was the better power spread.


mark
#438329 - 06/04/12 3:07 pm Re: opinions on recressed or pocketed valve seats? [Re: ]  
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Arnstein Offline
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Arnstein  Offline
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Mr.Gill. I think a lot of your "statements" and "facts" sometimes is so wrong they needs to be answered..Anyway,I end this discussion from my side with Rich B`s statement:" When I shut my mouth and turn to walk away,it does`nt mean you have won.It simply means you are not worth any more of my time."


Arnstein

BSA Spitfire MK3.800cc
Honda CB450T -71
Laverda RGS 1130cc -85
Ducati 1098 -08
#438392 - 06/04/12 9:37 pm Re: opinions on recressed or pocketed valve seats? [Re: BrizzoBrit]  
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Thanks Mark,

I'll be talking to the head man today. I think I just havent found the right person for the seats yet.

Will just go with the 3 angle cut and I'll get him to clean up the ports in the way suggested by EdV. Dont feel quite up to doing that myself yet. I reckon that building up the port floors is definitely a good idea and will consider that for the next iteration if I feel that I need to 'fiddle' some more. I would feel OK with doing that myself. I'm with you on your views you've expressed many times on keeping gas speed up.

I tend to run the bike, see what I am not happy with and work on changing that at each rebuild. At least (AFAICT) I've got the bottom end sorted finally.


Cheers
Ray


BSA 1969 A65F
BSA 1966 A65H
Triumph 1968 T120
Kawasaki A1R
& too many projects!
#438393 - 06/04/12 9:45 pm Re: opinions on recressed or pocketed valve seats? [Re: BrizzoBrit]  
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Adam M. Online content
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Adam M.  Online Content
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Mississauga, Ontario.
Arnstein, I think that finding the truth is much more important then who is right, so perhaps I ask about it in the new thread ?

#438537 - 06/05/12 5:12 pm Re: opinions on recressed or pocketed valve seats? [Re: Adam M.]  
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Arnstein Offline
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Arnstein  Offline
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Kristiansund. Norway
Adam M.
I agree..finding the truth is the most important.But,sometimes someone are tellin us "truth`s" that is wrong and at the same time claim to be right.Then it is maybe right to take action?

Too often will these who use a lot of words telling us sometimes nonsence and sometimes half the truth mixed with myths get away with it and think they are both right and truthful and at the same time fool others who believe all their words..


Arnstein

BSA Spitfire MK3.800cc
Honda CB450T -71
Laverda RGS 1130cc -85
Ducati 1098 -08
#438587 - 06/05/12 7:57 pm Re: opinions on recressed or pocketed valve seats? [Re: BrizzoBrit]  
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John Healy Online content
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Boston, Massachusetts
I have been reading along and find it amazing that anyone:
a. would believe "Road Tests".
b. would not realize that these bikes were highly massaged before a magazine got their hands on one.

I always thought that there's Truth, and then there is what is reported about the advertisers.


#438596 - 06/05/12 9:00 pm Re: opinions on recressed or pocketed valve seats? [Re: John Healy]  
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Magnetoman Online content
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Originally Posted By: John Healy
b. would not realize that these bikes were highly massaged before a magazine got their hands on one.
John, I would only point out that what you wrote implies the magazines accurately reported what they found with the massaged bikes. There is plenty of evidence this often isn't the case. Even today, one widely-published magazine writer invariably gushes that the present bike he is reviewiing is the most incredible bike he has ever ridden. He seems never to find a bike that is flawed.

I have complete collections of Cycle and Cycle World since they started publishing, and it's immediately obvious just by looking at them on the shelves that magazine profits are directly tied to motorcycle sales. In good years the companies advertise more, which lets the magazines print more editorial pages, both of which swell the pages. In bad years they contract in size (not just the number of pages, but also the height and width of those pages). Despite what publishers indignantly insist, it is simply not in their economic best interest to say bad things about motorcycles. There were many reasons to believe previous incarnations of Indian might fail, but magazines only recounted those reasons after they failed. Typically with a "we knew it all along" attitude. But, if they knew it, they certainly didn't write about it while the companies were still limping along.

The h.p. required to overcome air resistance goes as the cube of the velocity. Taking the top speeds previously posted in this thread at face value, if the Lightning indeed did go 112 mph, the Spitfire would have had to have (119/112)^3 = 20% more h.p. to reach 119 mph. While 20% is within the range of possibility for a highly massaged engine (assuming the Lightning hadn't itself been massaged, in which case the 20% would have had to come on top of a previous 10-20%), another possibility for that top speed is that BSA's advertising manager simply said something to the magazine's publisher like "Our sales office is counting on you confirming our tests that this bike goes 119 mph." Finding the correct answer is always easier when you're told what the answer is.

Nothing I wrote eliminates the possibility the Spitfire the magazine tested really did go 119 mph. Personally, though, I wouldn't bet on it.

#438604 - 06/05/12 9:23 pm Re: opinions on recressed or pocketed valve seats? [Re: John Healy]  
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shel Online content
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shel  Online Content
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ohio
Originally Posted By: John Healy
I have been reading along and find it amazing that anyone:
a. would believe "Road Tests".
b. would not realize that these bikes were highly massaged before a magazine got their hands on one.

I always thought that there's Truth, and then there is what is reported about the advertisers.



Are you implying that a T150T straight out of the crate wouldn't keep up with a Marshall's bike on the Isle of Manx?
Heresy, I say. shocked


When given the choice between two evils I picked the one I haven't tried before
#438607 - 06/05/12 9:35 pm Re: opinions on recressed or pocketed valve seats? [Re: BrizzoBrit]  
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John Healy Online content
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I have a couple of World class writers writing articles for Vintage Bike. Both, in their own way, indicated to me that they love writing for VB. They can write the article in the way they believe it should be told.

When they write for major magazines they say it takes a short time to write an article once the research is done. Then they labor over the article for hours, sometimes days, looking at how anything said might offend an advertiser.


#438609 - 06/05/12 9:37 pm Re: opinions on recressed or pocketed valve seats? [Re: BrizzoBrit]  
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John Healy Online content
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"Are you implying that a T150T straight out of the crate wouldn't keep up with a Marshall's bike on the Isle of Manx? "

Mine wouldn't!


#440263 - 06/15/12 2:06 am Re: opinions on recressed or pocketed valve seats? [Re: BrizzoBrit]  
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Posts: 72
Michigan
Polishing ports is ill advised for 4 stroke engines. 2 strokers like ports as smooth as possible. 4 strokes like ports that are a bit rough to prevent the a/f mixture from sticking to the walls.

Brit twin ports are too low to get a serious increase in flow because of the tight turn @ the valve.

An engine w/ higher compression will make more 'power' than a lower compression engine, all other things being equal, because compression converts into the force that drives the crankshaft.

Bumping the compression ratio is the least expensive way to increase power.

Horsepower gets you down the straight, but torque gets you out of the corners!

Last edited by dodgeboy57; 06/15/12 2:16 am.

45 M20
56 Ariel HS
56 Ariel HT5
(3x)57 B34 "Alloy Clipper" (Tri-Scr-ISDT)
58 A7 Bitza
61 Greeves Hawkstone
63 A10 GSS
63 Greeves MDS
65 Otter B40WD Trls
65 M&M B44(Miller frame/Dick Mann eng)
67 Greeves MX5 ChallengerTT
71 B50/570cc MX
#440290 - 06/15/12 10:54 am Re: opinions on recressed or pocketed valve seats? [Re: ]  
Joined: Jul 2009
Posts: 3,549
Pete R - R.I.P. Offline
In Remembrance
Pete R - R.I.P.  Offline
In Remembrance

Joined: Jul 2009
Posts: 3,549
Vic. Australia
There's not much difference in flow between a rough cast pipe and a polished one.Shape matters more.
I remember back in the '70s,reading about flow-bench guru Jerry Branch deliberately sinking valves 0.100" in an A65 head to get more flow and more power.I've probably still got the magazine somewhere,with pictures of a finished head.There would have been more involved than your average sunken seat.

You can always shim valve springs to get correct pre-load.You can adjust valve length to fix rocker geometry,provided you can do the geometry to prove it's necessary.

The restiction around the valve guide is not a restriction until you approach 1/2" valve-lift.At 0.400" lift the only restriction is the valve itself,not the port.

I wouldn't say XS 650 Yamaha carbs were vastly superior to 30mm concentrics.They had a big butterfly (38mm),but at the needle they had a cross-section equivalent to 30.5mm diameter.

I don't give much credibilty to the idea of small ports and small carbs giving higher top speeds.I see it as wives' tales and pub talk.The ports may be big enough,but who's using small carbs and ports on a race bike?

#440311 - 06/15/12 1:50 pm Re: opinions on recressed or pocketed valve seats? [Re: BrizzoBrit]  
Joined: Nov 2007
Posts: 72
dodgeboy57 Offline
BritBike Forum member
dodgeboy57  Offline
BritBike Forum member

Joined: Nov 2007
Posts: 72
Michigan
Without going into a detailed Doctorial thesis,a uniformly 'rough'(200-300 grit) intake runner (4 stroke) will flow better than a 'polished' runner the same way the dimples on a golf ball decrease drag: it's all about laminar flow!

In my experience, we used computers and CFD (computational fluid dynamics) to create 'optimized' ports in our CAD models and thus the actual head. Our 'flow' guys were constantly decreasing the size of the runners to increase flow.

Flow is more 'black art' than 'science' IMO.

Last edited by dodgeboy57; 06/15/12 5:14 pm.

45 M20
56 Ariel HS
56 Ariel HT5
(3x)57 B34 "Alloy Clipper" (Tri-Scr-ISDT)
58 A7 Bitza
61 Greeves Hawkstone
63 A10 GSS
63 Greeves MDS
65 Otter B40WD Trls
65 M&M B44(Miller frame/Dick Mann eng)
67 Greeves MX5 ChallengerTT
71 B50/570cc MX
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