Substitute 7.3:1 scratched pistons by 8.1/1 or 8.3/1 Pistons
- Thread starter Moca
- Start date
Hi Howard, that was just the way that they all worked out. This has been the way I found it for decades so many of the pistons were the old style, long skirt Hepolite or whatever. I have not done it with any of the more modern short skirt, low expansion pistons yet so they might be lighter. Some of these would have been either 9:1 or even 10.5:1 s and so might have been a bit heavier than the original 6.8:1s. The holes were always rather small, about 1/4" or 3/8" from memory. I always used the same spring balance to weigh everything, con rod small ends, pistons etc. so even if the spring balance was not spot on at least everything was consistent. Am I to understand from your posting that you have done this and not found the need to make holes? If so what about others out there? Remember chaps, feedback and exchange of experiences is to all our benefit.
No, I don't get involved in anything that technical, I leave it to people with much more experience. I was just curious why the flywheels needed changing to keep the original balance factor. When Tony Maughan rebuilt my crank I don't remember supplying him with the pistons, but it is a very long time ago so the job must have been up to his usual high standard.
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Thanks guys,
Back to the original subject, I have bought the Club's 7:3/1 ,the bigger ones were not available, what would it be the ideal clearance to the sleeves , in mm please.
Always amused, and thankful for everyone's participation.
Yours truly,
Francisco
Sent from my iPad using Tapatalk
Back to the original subject, I have bought the Club's 7:3/1 ,the bigger ones were not available, what would it be the ideal clearance to the sleeves , in mm please.
Always amused, and thankful for everyone's participation.
Yours truly,
Francisco
Sent from my iPad using Tapatalk
If you either have, or have access to, the correct facilities it is really important that you check that the cylinder bores are perpendicular to the base of the cylinder muffs. Very often they are about five thou out. This can be checked by setting up each cylinder between centres with plugs in each end into which centres have been machined. If you cannot do this yourself find someone near to you who can. Then check with the people you bought the pistons from to ensure that they are low expansion pistons and what the recommended clearance is. If they are low expansion then it is likely that the recommended clearance is 3 to 3.5 thou. That is .076 to .089 in millimetres. You can imagine that if the base of the muff is out and the cylinder is inclined to either the right or left side of t he bike then that is why low expansion pistons melt. If everything is alright and you ensure that your valve guides are in good order or sealed then oil consumption will be negligible. Even Albervin's clearances above will not save you if the bores are really tilted.
My Morini runs on 11 to 1 comp.- even on 95 octane fuel-so old fashioned head designs a la vincent or triumph I suggest run better on a lower comp! My old 'B' rapide outfit has compression plates under the barrels-It probably is about 6 to 1!! It is certainly not fast but never " pinks"!
In Australia a lot of us run an extra thou or even 1.5 thou (inches) clearance due to the weather conditions. At the same time we also make sure we have a sufficient interference fit between liner and muff. I have never had an oiling issue with those clearances. Just run the bike in as per recommendations and you should be OK. The hone marks on my bore were as new 15,000 miles ago when I rebuilt the engine last month. Note the rebuild was due to a breakdown in the crankcase sealant between engine and gearbox. That was cured with Three Bond sealant.