"Y Alloy" Pistons
- Thread starter redbloke1956
- Start date
I have nipped up a brand new Specialloid,carefully run in, with a new,well-fitting muff and liner running .004" bottom skirt clearance. I fitted a new Club piston and gave it .006" clearance and have had no problems even in heavy traffic on a 100 degree Fahrenheit day. If you ARE using a Y alloy piston read the paragraphs on Piston Clearances in "Tuning for Speed" but remember what I keep saying about modern fuels apparently burning hotter. Even if you are using a close tolerance piston I would go looser than recommended.David Dunphy certainly has the runs on the board and he gets no argument from me because I am not worthy to wash his footpegs, likewise Big Sid. I am sick of repeating ROUND LINER ROUND BORE SNUG FIT INTO CRANKCASE MOUTH also good head joint all gives the little heat devils someplace to go.I also use 95 or 98 octane fuels because a really goood engineer tells me to,and he has spent 50 years correcting other people's sorry mistakes on Vincents. Sorry if I'm sounding a little testy, I've had a trying day running in a new puppy.
Thanks Chankly , I am running a new muff, new liner and new piston, none of which are Y alloy.
The question on Y alloy is for another project I am currently working on but your info is relevant all the same, the liner in my Comet is not, unfortunately, a snug fit....the new liner has a cold clearance of probably 2 or 3 thou...not much I could do about that I am afraid.
The Y alloy piston that is in the current project has only about 2 thou clearance, which I hope to open up in the next few days, the engine has been running previously but I have no idea for how long as the previous owner has passed away, I am a comparative novice on this age of machinery and on a steep learning curve, relying heavily on the experience of others especially when it comes to finding information that is disappearing along with REAL mechanics and engineers.
I fully understand how us "newbies" must frustrate the bejesus out of those of you who have owned/repaired/fettled these machines for many years, but we all have to make a start somewhere, I for one would have owned a Vincent 40 years ago if I had, at that time, the wherewithall to do so, as it is I almost had to sell one of my children to purchase what turned out to be an overpriced lemon of a Comet.
So please understand my confusion when the responses received for clearances/expansion for a Y alloy piston range from 4 thou to 20 thou, especially since this engine has already been running with only 1.5 to 2 thou clearance.
I am relying on the input from those with far, far greater experience and knowledge than myself and am very grateful for it.
Thanks to all
Kevin
Hello Kevin, I think most of us have found out the Hard way !! No matter how long we have been doing it, Vin's are not like other bikes, Any luck with those forks yet ? Cheers Bill.
Just a bit of further information. P.E.I.'s clearance recommendations work out to about .009" bottom skirt "Y" alloy in an iron barrel and about .006" for an iron liner in an alloy muff: all based on about 84mm. bore.
On Specialloid skirt clearances for racing , in my case drag racing . Went together at 6 thou , after a few runs it showed nearer
7 thou . No problems with fouled plugs or smoking . Never showed picking up . Was a bit of slap heard when cold . Long lived very reliable pistons these even at 13 to 1 on methanol . Our Vincati has a set in it at 10.06 to 1 . Very quiet and powerful .
Lola has a set in it at 10 to 1 . Many runs , no problems so far . Sid .
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7 thou . No problems with fouled plugs or smoking . Never showed picking up . Was a bit of slap heard when cold . Long lived very reliable pistons these even at 13 to 1 on methanol . Our Vincati has a set in it at 10.06 to 1 . Very quiet and powerful .
Lola has a set in it at 10 to 1 . Many runs , no problems so far . Sid .
Sent from my iPad using Tapatalk