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Re: L F Harris Pistons/Rings [Re: tbird649] #691681 04/14/17 3:06 pm
Joined: Mar 2005
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Triumph Service Bulletin Hone Cylinder

Further to preparing the cylinder the angle of the cross hatch is important. If it is too shallow it will hold too much oil. This can lead to the cylinder surface becoming glazed, prevent ring break-in and also hamper the natural rotation of the ring slowing down break-in. If it is too steep it will let oil drain from the walls during off use and excessive ring rotation leading to excessive wear. Typical cross angles are between 22° and 32° measured from the horizontal.

Before the cylinder is installed it should be washed in hot soapy water using a scrub brush. Small bits of honing stone get embedded into the cylinder surface. We used to use the solvent tank to clean the cylinder but the hot soapy water routine has been shown to do a much better job of removing any left over bits of honing stone. Any one doing this for any length of time will have seen a piston, and sometimes rings, with very fine striations on the wear surface. Often it is thought it was caused by sucking in some dirt, but upon further inspection it has been shown to be from improper cleaning of the cylinder bore. The drill is you wash and scrub until a lint free paper towel, or rag, can be rubbed on the bore and come out perfectly clean. When in doubt clean it some more. Then take a lint free rag with a couple squirts from the oil can on it and rub it on the bore. This is your first step in "drier" assembly - note I did not say "dry!!"

When you read all this, one should become familiar with a term you NEVER hear today but was included in every technical engine publication I grew up with: "Blue Print." It was accepted that the factory DID NOT manufacture the engines "to the drawing." It was assumed that things weren't square, true and round. When building a motor to perform it was normal to check for, and correct, any problems.

Just as we would not build a Triumph racer with out correcting the bore in the cylinder we would not assume the crankcase mouth was parallel with the crankshaft center line. People giving you advice on grey cast iron rings today assume your cylinder bore geometry will be true to at least 0.0005 and for steel or ductile iron as little as 0.0002". It often doesn't cross their mind that you are working on an air cooled engine who's bore, once warmed up, can go out of round a lot more than 0.0005" and the bore is not at right angles to the center line of the crankshaft.

Triumph didn't use 150 grit in production engines because they were stupid. They did it because the production machinery could not hold tolerances anywhere near 0.0005" let alone 0.0002". Further they were doing it for a price on machinery that had been used hard to help win a war. It is a tribute to the talent of the British workforce that they did as good as they did with what they had to work with. Dead clever lads they were. Blueprint your engine and then talk about 280 grit and planar honing.


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Re: L F Harris Pistons/Rings [Re: John Healy] #691738 04/14/17 11:14 pm
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Originally Posted by John Healy
Triumph Service Bulletin Hone Cylinder


Just as we would not build a Triumph racer with out correcting the bore in the cylinder we would not assume the crankcase mouth was parallel with the crankshaft center line. People giving you advice on grey cast iron rings today assume your cylinder bore geometry will be true to at least 0.0005 and for steel or ductile iron as little as 0.0002". It often doesn't cross their mind that you are working on an air cooled engine who's bore, once warmed up, can go out of round a lot more than 0.0005" and the bore is not at right angles to the center line of the crankshaft.

Triumph didn't use 150 grit in production engines because they were stupid. They did it because the production machinery could not hold tolerances anywhere near 0.0005" let alone 0.0002". Further they were doing it for a price on machinery that had been used hard to help win a war. It is a tribute to the talent of the British workforce that they did as good as they did with what they had to work with. Dead clever lads they were. Blueprint your engine and then talk about 280 grit and planar honing.


Being a hobbyist with limited experience I built the Triumph "race" engine just like I would build a Chevy V8. And the Chevy has sloppier machine work and more of it....If you want to get the best out of the engine it has to be jacked into shape by making sure all the parts are square and true to each other. The hard part is finding a shop that will jig the engine cases for any machining.... It cost me, and the rider damn sill money to machine some of the parts...


79 T140D, 96 900M Ducati ....On a bike you can out run the demons..
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