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By stinkwheel
#83476
How tight can they be in the small end?

Just fitted one to my 350 bullet and while it slid through the small-end it took both thumbs to advance it. You can feel some resistance to the piston rotating on it (as in you can rock the piston from front to back with one finger but it stays where it was left rather than flopping from one side to the other).

I'm used to them being somewhat looser but maybe this is something that will "wear in" in the first few miles? Should ease off as the temperature increases too with steel in an alloy conrod.

Or should I take it apart again and relieve the small end slightly? I think it would just take a gentle rub with some fine grade wet and dry on the end of a finger.
User avatar
By stinkwheel
#83477
I should add, this is actually a NOS hepolite piston and gudgeon pin for a meteor but everything I see says the gudgeon pin diameter ought to be identical to a 350 bullet? Our hosts even list them as the same part number.
By Marko
#83544
Hi, recently there was a great big debate about this topic on the FB group "British motorcycle mechanics" - anyway, without boring anyone with tedious details: it is quite normal for a genuine old stock Hepolite piston for the gudgeon pin to be a tight fit in the piston, so when assembling warm the piston up (I use hot water), some people put their pins in the freezer to chill , & voila! job done. Don't get tempted to use a different, i.e looser fit gudgeon pin ;)
User avatar
By stinkwheel
#83562
Thanks for the reply.

Yes, it was a fairly tight fit in the piston but it's also somewhat tight in the small end too. As I say, finger-tight rather than the strict engineering definition of tight but I did wonder if there was room for an oil film in there. Took both thumbs to push it through. I'm used to a piston being a looser fit on the conrod.

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