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#735324 05/14/18 11:59 pm
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Hi, first post

New to forum and British bikes

I've got an a65 lightning who's inlet valves are clipping the pistos. Took head off and was going to dremmel away part of the crown, but wanted to ask how much does the timing need to be out for the valves to hit, and would it run that far out.

Or indeed does the timing need to be out for the valves to hit.

Cheers

Richard.

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A65's have a land ( raised area ) above the top fin
It is not uncommon to find the barrels machined down to be level or partially into the top fin.
Same story with the head .
Back in the day 10's and 11's were all the go for us who thought we were substantially better engineers ( and riders ) than we really were.
In any ase you will need 30 to 40 thou clearance measured satic between the piston crown & the valves when running or it won't run for very long.

So what is the history of this engine ?


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There are a couple things to check and to go over:


#1 - stock cams will not allow a valve to hit a stock piston

#2 - make your sure your valves are the stock length

#3 - make sure ALL your pushrods are the same length

#4 - make sure your cylinder head has not been milled

#5 - take your inner timing / gear box cover off and make sure your cam is installed and lined up properly. BSA is a "unicam" set-up, timed and ground accordingly from the factory

#6 - you can always put a degree wheel on the engine to check cam timing

#7 - if all check outs fine I would be inclined to see if your head has been skimmed

Good luck!


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CBS, I think you mean
#1 - no interference with the cam timing correct
#3 - exhaust pair and intake pair are equal (valve screws take out small variations)

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And I thought having a brit bike would be simple😟

Thanks for replays.

I bought the bike from someone who passed away and I didn't know so I have no idea of its history.

I don't like to speak ill of the dead, but I seem to spending a lot of time brining things up my standard, which isn't that high☺

I know the Bush the crank goes through was replaced and the engine has been rebuilt, but as I said, to what standard I don't know.

Barrel and head still have a chunkable size land/ridge/raised area before fins. So my plan of action is to relieve the piston crowns a bit and refit head and see how it runs. It did start and run relatively easy before but with quite a loud tapped noise. Now I know why.

If I think it's down on power I can investigate cam timing with head on.


Cheers

Richard.

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Originally Posted by DMadigan
CBS, I think you mean
#1 - no interference with the cam timing correct
#3 - exhaust pair and intake pair are equal (valve screws take out small variations)



ok so we are talking about an A65....... My mind is Triumph 650 programmed


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Check cam timing first. Not that big of a deal. In standard form there is lots of room. PRT

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some times it can turn out to be a real thin cylinder base gasket or head gasket so of the new head gaskets are real thin compared to the old ones...............what the above have said about plaining too much odd barrels/head is right as well

if its not the timing try a thicker cylinder base gasket and let us know how thick the copper head casket is


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Exactly where is the valve "hitting" the piston. a. on the face of the valve pocket. b. on the side of the valve pocket where it is cut into the top of the piston???

Which valve is hitting the piston: a. the intake b. the exhaust?

Is either valve oversize Stock valve sizes:
1962-1965 intake 1.470" exhaust 1.410"
1966-1971 intake 1.598" exhaust 1.410"

If any of the valves are of a commercially available oversize the dimensions above would be plus .060"
for example a 1972 intake would be 1.598" + .060" = 1.658"

In some case the diameter of the valve pocket in the piston MIGHT have to be increased to accommodate the oversize valve. This is done without removing any material from the face of the valve pocket. This is where some PlayDough (kids play clay). Put some between the valve and the piston. Turn the engine over once and measure the clay.

Removing material from the face of the valve pocket must only be done knowing that the piston area under the face MUST be at least .125" thick.
Before removing any material from the face of the piston's valve pocket I strongly recommend that the thickness of the piston in this area be measured. You will need at least .040" clearance between the face of the valve and the piston (.060" is even better) and have the thickness of the piston under the valve pocket at least .125".

Once you check that the valves are standard you must then determine if the cam timing is correct (this get a bit fussy when you do not know if you have other than a stock cam - where all you have to do is align the dots) and neither the head or cylinder has been cut. If it is a accessory cam then you can take opening and closing figures and lift and see if you can match it up with known cams. Also you can time the cam so the intake and exhaust lobe centers are around 102° to 104°. The cam might work to its full potential, but few people could tell the difference.

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I had a similar experience with my A65 after the pistons were replaced. Since you don't know your bike's history, yours may have been replaced as well. My problem was that the intake valves were catching the raised valve clearance portion of the piston as it was moving down and making a "clicking" sound. Increasing the radius of the cutout slightly (.020") using a Dremel solved the problem. You should see the light scrape marks of the valve on the inner raised section of the piston valve cutout if this is the case. If your head is still off, this will be a quick check.

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Cheers guys.

I'll take some photos and try uploading them tomorrow

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Shouldn’t have a problem wth your pistons, valves, cylinder or head..

Those are some nasty impressions there and would benefit from being smoothed out to stop any pinging. First thing I would do is check your push rod lengths, maybe you have some A50 exhaust rods used as inlets (inlets are shorter than exhaust) with a stock cam you can advance/retard the cam by more than a tooth, I was supplied with an A10 crank pinion when I first built mine, pulled well... but some years later when I dialled the cam in properly I found I was 20 degrees advanced at the cam (that’s over one tooth) I could still turn the engine over if I advanced it further or regarded it a tooth past where it needed to be. It’s still worth checking you have the correct components in there.

But what I’ve found will effect it is too big a cam positioned wrong or using the wrong followers or push rods the wrong length.


Now let’s all have a beer beerchug

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In the first pic it looks to me like the pistons are fitted the wrong way round , the big cut out in the pic is on the exhaust side. The big cut out should face the other way.


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Who said a picture is worth a million words.

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That's good news and bad news ... Good news is you may have found the present problem.

Bad news is that if the same guy that didn't do things to proper standards (as you've noticed) AND put the pistons in backward, also installed the lower end of the engine including the timing side bushing, then it might need to come all the way down. Installing that bushing is a specialist job - someone who's an expert on Sportsters, Triumphs, and small-block Chevy cranks can screw up a BSA bottom end something fierce if he doesn't understand about end-float, bushing clearance, and line-boring ....

When you take the cylinder off to reinstall the pistons, at least check the end-float of the crank to see if it's in spec ....

Lannis


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I put my specs on this time, I see the writing on the piston is the right way up, my eyes might have been fooled by the cut outs,, possibly cam timing is advanced by a couple of teeth, pull timing case to check. Better check the inlet valves still seal, I would be surprised if they are not bent. Doesnt bode well.

Last edited by gavin eisler; 05/16/18 8:17 pm.

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Cheers

The piston cut outs look identical inlet to exhaust to me.

On this basis one is right way round one isn't because the writing is one way on one and t'other way on t'other


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I noticed during disassembly the odd way the timing gears are marked for timing,offset which according to my manual is correct,any one know why they did this and not just mark the gears like most do with a mark where they are in complete contact?


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Two head gaskets is a quick fix! How thick was the last head gasket, was it one of the solid copper one's or one of the composite gaskets? How thick was the used gasket?


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The head gasket is about 1mm thick solid copper.

Looks like the side casing is going to have to come off.


If thiat wasn't enough, my daughter's car has just threw its timing chain and my other half has informed me that this is more important than a stupid old bike. 😞


Cheers

Richard

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I'd carefully measure the cutouts in the pistons with a pair of calipers. Intake valves are always bigger than exhausts.


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Originally Posted by Frogeye1000
The head gasket is about 1mm thick solid copper.


If thiat wasn't enough, my daughter's car has just threw its timing chain and my other half has informed me that this is more important than a stupid old bike. 😞


Cheers

Richard


If that's what she told you, you'd best pay attention! help Although if it's an "interference" engine, you'll be looking for either a new engine or another car!

Sorry about the bad luck, seems to be the way it happens ...

Lannis


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After you have scrapped the car remember to pull the tach drive before trying to lever off the inner timing chest.


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It's a fiat 1.3. Valves do hit piston, however they are perpendicular to them so the shock is sent through to the rockers which snap, which should make the job easier. That is if you don't snap one of the injector clamp bolts in the head.

In which case.............[img]https://flic.kr/p/25T63CZ[/img]

Managed to get New engine from a Corsa van for £250 with 61000 miles on it and fsh from a friend of pub landlord.



Now on to more important things.

I know the Bush was done by an old chap who has a small precision machining company and is held in quite high regards around here. Don't know whether he built up bottom end though.

The pistons just look like they have two identical flat chambers on them. How do I tell if one is bigger than the other, but like I said earlier they are fitted different ways round anyhow according the the stamped writing on the crown, and both are being hit.

I'll see what I can get done next week, but as you can see, I'm a bit busy now😟

Cheers

Richard


Last edited by Frogeye1000; 05/17/18 4:44 pm.
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