Ay up folks, just rebuilt my 92 Yam mono engine with new mains, big end, con-rod, gudgeon pin, crank seals etc. Also put a s/h 270 barrel and head (higher compression looking at the facing) with shortened inlet tract on it. Rode it yesterday, powerful but pinks like hell and from idle it doesnt rev cleanly, only a little bit but its not smooth. Any ideas?

Eiger

I would jet the carb and run a strobe on the timing

Dave

Eiger

this is all from memory so it will pay you to talk to Birketts 01229 716806. But the 270 barrel will have had the base skimmed to make the the larger piston work. This is because the distance between the gudgeon pin and the top of the piston is about 2mm less on the TY 250 Twinshock piston (the twinshock piston had a bore of 70mm not 68mm) which was often the piston used. If the barrel has been skimmed and the correct piston used the timing should be ok but you may have to adjust carb.

You should be able to check the barrel has been done correctly by taking the head back off and at the pistons lowest point the top of the piston should line up with the bottom of the exhaust port. At the top of the stroke the top of the piston at the outer edge should line up with the top of the barrel.

The other thing to check is that the reed block didnt warp when it was cut and welded. This happend on my pinky but was fixed by fitting two gaskets. Just check its all square where the reed valve bolts on to the block.

Cheers folks I'll have a look at the timing anyway and check what you've said Baldilocks, never knew they used the twinshock piston, good info. Cheers gents.

Regards Eiger