84' Yamaha TT 600 makes noise under "load"

Recently my friend rebuilded my '84 Yamaha TT 600, bottom end etc.

New main bearings, crank case bearings, some new gears, crank pin, conrod, Wiseco 11.5 to 1 piston off ebay (actually got it cheaper than stock piston) Obviosly new gasket set. I have done 180km with the bike after rebuild sofar, and the Clymer manual reccommends 1000km after that I can use it pass half throttle. I am doing exactly what the manual describe. But if I accelerate a bit quick and getting near half throttle it makes a noise like the compression want to push out at the top gasket. Could it be the new piston still "settling in" Cant see oil residue anywhere near the top gasket. My friend used the info from the manual to torque the head accordingly, even a little bit more cuz I have now a 11.5 to 1 piston instead of a standard 8.5 to 1 piston. Is this normal, will this go away eventally after I have done the 1000km's? or should I be concerned?

See what it's like after a few more KM. Rings might be a bit stiff still. Oh but how I envy you with that piston. Knowing SA's petrol...ja, sê maar net eish. I bought a tankful of Caltex for my five-fiddy the other day, and I got some horrible backfiring and surging with it. I suspect water in the fuel but what do I know - I'm just a chancer, according to the general manager...

Yip as I suspected, it is blowing out the side at the top gasket, if I whack the throttle. I have used a Versah top gasket set. I reckon that should be fine with a higher compretion ratio or do I need a different gasket set. I probably have to re-torque the head again.Any one of you guys had this problem before???:p

See what it's like after a few more KM. Rings might be a bit stiff still. Oh but how I envy you with that piston. Knowing SA's petrol...ja, sê maar net eish. I bought a tankful of Caltex for my five-fiddy the other day, and I got some horrible backfiring and surging with it. I suspect water in the fuel but what do I know - I'm just a chancer, according to the general manager...

Eishh, I feel your pain!!! fellow citizen. I bet you he fill's his beemer at a different petrol station:smirk:

Beemer? That's the car for plebs these days, as far as the general consensus goes. I think he drives a Porsche Cayenne IIRC. And he has a nice big boat, forever standing in the way of willing customers. Some people would recommend a thicker gasket, but it's more a case of whatever floats your boat. Thinner gaskets would mean an even higher CR, but at least we have a octane of 95 here, so it should be resistant to detonation as long as there's no water or additives or dagga leaves inside. I was looking into boring my sleeve and throwing in a Wiseco 11.5:1 piston, but scrapped that idea since the 550's use an iron liner, unlike the 600's. Only diff is the bore, really (92mm vs 95mm if my memory serves me correct)

If you twist the throttle really fast from an idle position and it makes a sort of banging noise (like the bigends have gone) then I'd say blown head gasket. Maybe the two surfaces need plainning to make sure their mating correctly.

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