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#198188 - 04/08/07 7:11 am 750 stroker motor/90 degree crank conversion  
Joined: Mar 2007
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Beezer Bob Offline
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Oregon
I can't get over this fasination with stroking a A65 with a A10 crank. Probably will never do it but would really like to know more about doing it. As I understand it, an A10 crank is fitted to cases from an A65. Do the cases need to be converted to roller bearing? The standard A65 rods and cylinders are used but Triumph T140 pistons are used. The A65 cylinder is bored out to accept the T140 pistons, how much? The heads are ported out to 32 or 34 and larger valve are installed. Are there valve clearance issues with doing this? What happens to the timing? Does anyone have any information on this modification like performance increase?

#198189 - 04/08/07 7:26 am Re: 750 stroker motor/90 degree crank conversion  
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BONZO R.I.P. Offline
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Michigan, USA
You have overlooked what I think is one of he more substantial problems with this , being the alternator on the drive end . the Triumph pistons will need to be modified at the skirts to clear the flywheel , timing is gonna be a black art ,carburettor as well , bearings will be a matter of what year A-10 crank you are using (later big journal cranks are prefferred) balance factor may be another "black art" i havent heard a definitive answer on this . Havent heard or done much with the heads on these , but that is the stuff for prs . Also , Ed V. may be able to help with pistons for a project like this , as I recall , he sells the max size A-70 pistons ad he is one of the few that really knows his way around these things ...
FWIW-BONZO

#198190 - 04/08/07 11:12 am Re: 750 stroker motor/90 degree crank conversion  
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Mark Parker Offline
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Bega NSW Australia
Fitting the alt is not a major problem, the crank is just a bit short and can be drilled and tapped for a bolt to retain it, and a bit of a sleeve put on the crank at the thread I think. The 'big journal' I think referes to the big ends, the main is still under A65 size, and a roller conversion is a simple solution. A70 pistons should have the right angled valve reliefs T140 ones need modifying. I did run a motor with an A10 crank for some years and it was good, however my experience of late is that a std stroke A65 crank, (easy to come by) can make a gem of a motor if converted to 90deg. Running this with a big bore kit is in some ways a better setup, mainly because it breaths better and can pull RPM. The inherant advantages of the short stroke A65 can be capitalized on. Between older British 750s the A65s stroke of 74mm is the shortest after the 3 cyls, 90degeing it makes it pull stronger right through the rev range and spin smoother at the top, in my estimation reducing dynamic load on the crank and bearings. The 750 motor we have recently been testing was at 8,400RPM before I realized it when checking mainjet size. So even with just staying at 650cc going 90 is another fun thing to try with these motors which is an alternative to going A10 crank, either one just about neccecitates installing good rods to be safe.


mark
#198191 - 04/08/07 5:22 pm Re: 750 stroker motor/90 degree crank conversion  
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Beezer Bob Offline
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Oregon
The 90 degree crank sounds interesting, faster rpm pickup and better breathing with less stress on the crank. What is involved in this conversion. I think this one sounds do able. Is there someone in the US who can do the crank and about how much will it cost? Is there any place to get information on the conversion? As you can tell a kinda new at hot rodding a BSA. for years the only thing I was concerned with it starting easy not leaking oil.

#198192 - 04/09/07 1:00 am Re: 750 stroker motor/90 degree crank conversion  
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Mark Parker Offline
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Mark Parker  Offline
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Bega NSW Australia

Naturally the crank has little flats milled for where the H/Tensile bolt heads and nuts rest, the larger bolts through the crank pins are threaded into the sludge trap plug on one end, and into the crank on the other, and has no sludge trap fitted, it's necessary to sculpt the outer web on each side to fit this bolt which has the head ground on one side to allow it past easier, a cap screw headed bolt would make this easier. The oil slot lets the oil through to the second crankpin. Its ballanced like 2 singles with counterweights bolted to the new flywheel opposite each pin. We ballanced at 50% originally with std A65 +040 pistons but it seems smoother with the lighter big bore pistons so a factor of 55 or 60% may be better. We are planning to do a couple of cranks soon so will be set up to turn centre sections, if you want one. I was talking with Gary at SRM just recently and there could well be a billet ready made std stroke 90deg crank available from them toward the end of the year.



mark
#198193 - 04/09/07 10:31 pm Re: 750 stroker motor/90 degree crank conversion  
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blimey-bill Offline
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Somewhere in New Jersey
I'd like to give this a whirl myself sometime in the future. For my current project I'm sticking with the long stroke set-up. I wonder if SRM will produce a camshaft as well to work with the 90 degree crank. The ignition set-up is another consideration too when converting to 90 degrees.


'67 BSA Spitfire
'68 Commando Fastback
'75 T160 Trident
'02 Moto Guzzi LeMans
#198194 - 04/12/07 4:59 am Re: 750 stroker motor/90 degree crank conversion  
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Redman Offline
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San Francisco
Hey Mark...how did YOU deal with ignition? Just mod a Boyer pick-up plate or the rotor or...???
My next winter project will be the conversion to end feed oil delivery and 750ccs and 90 crank.


Life is short but very wide.
#198195 - 04/12/07 8:19 am Re: 750 stroker motor/90 degree crank conversion  
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Mark Parker Offline
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Bega NSW Australia
Hi Redman,
I've tried a few variations on ign, first was a Lucas Rita, all I did was grind one trigger bar off and weld another on at the correct angle. This works ok but there are idle sparks at odd angles, which when they were eliminated made for a crisper sounding engine. What I did was to mount 2 trigger coils off a honda 250 on the timeing case itself then welded a bar to an auto adv unit, used 2 transistors switched by the trigger coils to fire the coils, getting a single spark at the cyls only when needed, advanced by the mechanical unit. Someone who knows something about electrical components could probably make it better, but it worked. The only problem was the out of ballance bar, which wears out the adv unit after a fairly high milage. Next I did away with the mechanical adv mechanism made a double trigger bar, like a std rita, and wired in the honda ign modules, the reason for the double trigger was to mimic the honda triggering off the crank so the adv would work when needed, so this system has an idle spark but not at odd angles, as its a duel system. Trispark make single fire igns for Triples and could make one for a 90deg twin, but they are a bit expensive, though no doubt good. They fire only when needed with no idle spark at all, to me this sounds the best set up for a 90 or a triple.


mark
#198196 - 04/13/07 12:59 am Re: 750 stroker motor/90 degree crank conversion  
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Beezer Bob Offline
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Oregon
Does anyone have a machine shop they would recomend to do the machine work on the crank? This is a little more than I can do here at home and I'd rather not take to just any shop. I'm in Los Angeles, Ca. USA.

#198197 - 04/13/07 11:03 pm Re: 750 stroker motor/90 degree crank conversion  
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blimey-bill Offline
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Somewhere in New Jersey
I'm probably going to use Frank Deihl at Classic Cycle Works, but he's on the opposite coast from you.


'67 BSA Spitfire
'68 Commando Fastback
'75 T160 Trident
'02 Moto Guzzi LeMans
#198198 - 04/14/07 1:22 am Re: 750 stroker motor/90 degree crank conversion  
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Beezer Bob Offline
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Oregon
Thanks Bill, I'll get in touch with him and see what he has to say about doing this. If he knows what he's doing, it will be worth the shipping costs. I'm going to do this conversion on a spare motor so I can wait.

#198199 - 04/14/07 3:47 pm Re: 750 stroker motor/90 degree crank conversion  
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Gentry's Garage Offline
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LaLa Land in Cali
HiYa Guyz,
Changed the topic to reflect the way this topic is flowing. I have been researching rephasing the crankshafts for quite sometime. I though will go with 76* for mine....once I get my machinery powered!!!! Also not to leave a stone unturned I thought about the ignition end of things all the way from ridiculus and back again. I ended up with the thought of using mopar electronic ignitions (as I have had alot of luck with them in my musclecars in years past) and found that someone had already done it in OZ (gotta love Google)! I could not find his website on my notes, nor have I compared the Aussie Mopar ignition to the US as of yet..but don't think they are different. He is the one who has posted the A10 roller conversion and frame diminsions.

Happy Trailz,
Gentry's Garage

#198200 - 04/14/07 5:08 pm Re: 750 stroker motor/90 degree crank conversion  
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Beezer Bob Offline
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Oregon
In one of the posts I read on this, I thought I read that someone used the ignition of a honda. That would seem to me the way to go. You would think it was made to handle the vibrations and environment of life inside a motorcycle case. Replacements would be some what available and the price reasonable.

#198201 - 04/15/07 12:32 am Re: 750 stroker motor/90 degree crank conversion  
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Gentry's Garage Offline
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LaLa Land in Cali
panic posted April 14, 2007 12:02

Message: I've read some arguments for 76 degrees vs. 90
degrees, and they appear to favor 90 degrees.
In addition to the relative effects, 76 degrees is not an
absolute figure, but depends on the rod ratio. The 76 degree
figure was based on the appromate 2:1 ratio of the T120,
actually 2.013:1 for 75.62 degrees.
A Norton crank with Norton rods would not use 76 but 72.65
degrees, with the MAP "long" rods 74.02 degrees. To get 76
degree balance with a Norton crank the rods must be 7.24" -
not too practical.

Then Panic editied to say:I see no one is listening.

[ April 14, 2007, 13:17: Message edited by: panic ]


Panic comeon now don't give this attitude...I just can't live on the internet, I usually check things right befrore strarting work at 11:00pm PST.
I will adjust things to get the maximum piston speed wich is what I am going for, and will modify any part to acheive my goal. My main blockage point is getting the heads at a normal price...hence ALOT of stuff is going on eBay.
Bob, I think the Mopar pickup will survive..plus I know them.
Gentry's Garage

#198202 - 04/15/07 11:05 am Re: 750 stroker motor/90 degree crank conversion  
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Stuart Online content
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Scotland
Hi,

A question, if I may ...

Quote:
Originally posted by Mark Parker:
a std stroke A65 crank, (easy to come by) can make a gem of a motor if converted to 90deg.
Quote:
Originally posted by Gentry's Garage:
I though will go with 76*
... why did you choose these angles?

Reason I ask is, back in '94, the British magazine 'Classic Bike' ran an article with follow-up in subsequent issues on a T140 converted to 76 degrees. Aiui, the reason that bike had been converted to that angle was the requirement was perfect primary balance and that angle met that requirement given the T140's stroke and conrod length. Hence, would different stroke and/or conrod length require a different angle, or am I missing something?

Changing the subject to ignition - specifically electronic - has anyone considered talking to the guy who makes the Trispark? I know he's an Aussie wink but he is a T160 owner (as well as a clever electronics engineer), and he makes ignitions for 360-degree twins.

Regards,

#198203 - 04/15/07 11:59 am Re: 750 stroker motor/90 degree crank conversion  
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Gentry's Garage Offline
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LaLa Land in Cali
... why did you choose these angles?
Actually when the angles are so close 14*, its kinda like saying the USS New Jersey is a better battleship than the USS Iowa (they were sister ships) There has been all sorts of diagrams, engineering studies etc. The bottom line is the 90* appears (and probably is) smoother, but I feel that the slight vibrational difference (and I can't see it being that great) will more than offset by a quicker outta the hole/turn acceleration. I originally wanted to build both the 90* and the 76* bottom ends (swapping the top end ,including the pistons, between the 2) and dyno test both for HP and Torque, vibration and acceleration. That way there would be a real world side by side end all test of these two rules of thought.
Panic, I have thought some more and if 74.02 is were I get max piston speed I can move it up some!
Gentry's Garage

#198204 - 04/15/07 1:25 pm Re: 750 stroker motor/90 degree crank conversion  
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Rickman Online content
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Ohio
Gentry's Garage,
Email me offline wilya? I might be able to assist with the dual disc front end... And, what's the "VFD" you mentioned?
Brett
Rickman@columbus.rr.com

#198205 - 04/16/07 2:24 pm Re: 750 stroker motor/90 degree crank conversion  
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Stuart Online content
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Hi,

Quote:
Originally posted by Gentry's Garage:
when the angles are so close 14*,
Ok, thanks.

Regards,

#198206 - 04/16/07 6:36 pm Re: 750 stroker motor/90 degree crank conversion  
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JonS Offline
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Ive been considering a building an 850 Commando motor with a 90-degree crank for my Norton Atlas. I found a company called ED G Cranks (http://www.offsetcrank.com/index.html). They make and sell a 90-degree crankshaft for many British bikes.

When I inquired about building a Norton Commando motor with an offset crank Geoff at ED G Cranks replied with the following: You have to replace the crank and cams and modify a Boyer ignition system. The end result is a smooth engine with punchy acceleration because the crank is lighter in total weight and inertial weight. Torque and power output are identical but it winds up faster. 750 or 850, the difference is immediately noticeable. At idle the bike does not hop around on the centre stand and fenders don't vibrate. At speed the bike rides as it normally does but it does not vibrate until you go above 5000 rpm but that vibration is less then a stock 360-degree engine. With an isolastic-mounted engine there is no vibration. A solid mounted Atlas engine has some vibration but nothing compared to the stock engine.

Im assuming the above information would hold true with an A65.

Jon

#198207 - 04/16/07 6:45 pm Re: 750 stroker motor/90 degree crank conversion  
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Gentry's Garage Offline
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LaLa Land in Cali
I followed what Geoff did on his first crank on the Brit Iron list. He has built a special (really heavy!) jig to keep the crank from distorting while welding. The only way to get a stronger crank is a billet SRM.
Gentry's Garage

#198208 - 04/16/07 7:24 pm Re: 750 stroker motor/90 degree crank conversion  
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JonS Offline
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Does SRM make the same array of cranks?

#198209 - 04/17/07 4:10 am Re: 750 stroker motor/90 degree crank conversion  
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Beezer Bob Offline
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Oregon
I checked out the Ed G Cranks website. He does not only cranks but the cams to go with them. It's an interesting site. Crank and cam will run somewhere around $1600. It's worth taking a look.

#198210 - 04/18/07 12:32 am Re: 750 stroker motor/90 degree crank conversion  
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blimey-bill Offline
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Somewhere in New Jersey
Looks like ED G has a pretty good handle on ignition and camshaft mods for 90 degree cranks as well. The website states that they'll be offering a "monster" BSA crank with 89mm stroke. I'm not buying another set of rods so 84mm is my limit.


'67 BSA Spitfire
'68 Commando Fastback
'75 T160 Trident
'02 Moto Guzzi LeMans
#198211 - 04/18/07 3:25 pm Re: 750 stroker motor/90 degree crank conversion  

**DONOTDELETE**
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"reason that bike had been converted to that angle was the requirement was perfect primary balance and that angle met that requirement given the T140's stroke and conrod length. Hence, would different stroke and/or conrod length require a different angle, or am I missing something"?

No, IIRC that's what they said - but it's wrong, they don't know the math.
The purpose of the 76-type offset has nothing to do with a specific angle. It's the point where the weights are disposed so that 1 piston is dead stopped at TDC and the other is at maximum velocity. This is entirely a function of rod ratio - nothing else, not brand, not size (for the engineers: piston pin offset has effect of almost zero here, so I've ommited it). To determine this position:
Balance angle = 90 degrees minus the maximum thrust angle
Maximum thrust angle: inverse tangent of (1/(2*rod length)/(stroke length))
Example: T120 rod = 6.500", stroke = 3.2284"
(2*rod length)/(stroke length) = 4.027
1 / 4.027 = .2483
arc tan .2483 = 13.95
90 - 13.95 = 76.05 degrees.

However, the T140 is different:
T140 rod = 6.000", stroke = 3.2284"
(2*rod length)/(stroke length) = 3.717
1 / 3.717 = .2690
arc tan .2690 = 15.06
90 - 15.06 = 74.94 degrees.

The T120 is 76 degrees, but the T140 isn't.

Note that Ed G specifies 76 for all Triumphs and 74 for Norton:
Norton rod = 5.875", stroke = 3.504"
(2*rod length)/(stroke length) = 3.353
1 / 3.717 = .2982
arc tan .2982 = 16.60
90 - 16.60 = 73.40 degrees.

What, can all those experts be wrong?
Yes, they are. AFAIK no one has intentionally built 2 engines with the exact offset and the "rounded off" offset, and compared them for vibration.
Until that's been done, and the margin of accuracy established by something more than "yup, ah guess that's good enough", how do you know that the exact angle does not provide dramatically better results?

And, please: exactly which Honda has 76 degree firing order?

#198212 - 04/18/07 3:41 pm Re: 750 stroker motor/90 degree crank conversion  

**DONOTDELETE**
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To do this on a scientific calculator:
1. rod length (enter)
2. times 2 (enter)
3. divide by stroke length (enter)
4. invert (1 / X)
5. click "Inv" box, then "TAN"
6. subtract 90
7. result is offset angle

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