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serious problem on my SP2 rear cylinder stalling and pressure build up is blowing the rocker gasket out,been advised to check valve clearances then balance throttle bodies,has anyone else had this problem.. wales trip coming up so need to sort out pretty sharpish....

Can valve clearences be the problem? Sounds like you have excessive crankcase pressure which can be caused by worn rings but to be honest, a well maintained vtr motor can run up some serious mileage . Is the breather blocked/checked all the hoses etc, is it blowing oil out of anywhere else?

valve guides being as its only the one cylinder i would have thought that the clearances would affect gasses into the exhaust or inlet only. Cylinder head gasket could be another one. Just ideas

my mate who prepares race engines basically said throttle bodies out of balance can cause the problem but do valve clearances first so as engine at spec for balancing will check crankcase breather hose as well choice of many under the bike.... thanks for other thoughts though.....

steve p wrote:valve guides being as its only the one cylinder i would have thought that the clearances would affect gasses into the exhaust or inlet only. Cylinder head gasket could be another one. Just ideas

Cant realy be the valve guides since the valves will be shut when there is pressure, and any pressure that passes a valve would go into the inlet or exhaust ports.

Normally back pressure like this is a fooked piston/rings or head gasket, cracked head. Something that allows compression into the crank case. But when the flame ring goes on the head gasket it usually pressurises the coolent system not the crankcase.

If its as bad as you say then take the oil filler cap off and see if it puffs out there.

If an inlet valve was bent/ miles out of adjustment then I guess it could pressure the air box and then back through the breather into the crank case but to blow the gasket out before blowing off a hose seems strange. Be interesting to see if your air box is full of oil.

i'm going to start taking it apart and check valve clearances as they are long over due,i'm leaning towards a tight valve clearance then will be balancing throttle bodies as they have never been done either will let you know what i find,many thanks for the input i love this sight...

rear valve clearances are as follows inlet 0.12mm and 0.14mm, exhaust both are 0.26mm

sparkysp2 wrote:i'm going to start taking it apart and check valve clearances as they are long over due,i'm leaning towards a tight valve clearance then will be balancing throttle bodies as they have never been done either will let you know what i find,many thanks for the input i love this sight...

When you have the spark plugs out stick a compression tester in there, and when you get the air filter box off spin the coont over with the plug caps off and see if she spits compression out the inlet, you might even be able to see in there to see if the valves are closing ok.

Any updates, is it fixed?

putting back together tomorrow all clearances were tight have just picked up new shims then will balance throttle bodies,also found that the front spark plug was loose so should be like a new bike .....lol