QuestionBill, thank you for the thread on carbs as I had the problem you mentioned were the overflow tube in the float bowl was fractured. A weird problem but I replaced the float bowl to fix it, thank you. Makes me wonder how a fracture occurs, interesting.
I bought my bike which has sat for 15 years and has 18K miles on it. With the carbs rebuilt it now runs but I soon discovered a blown head gasket. Do you have any tips on insuring a good installation? Is the head gasket problematic on this model and do I need to replace the base gasket at the same time? And yes I know the engine is coming out of the frame.
Thanks...
AnswerDave, glad that you got the carb problem fixed up okay.
I am not sure to what extent you mean "blown" head gasket. Inline fours have a tendency to leak oil at the edges of the gaskets, due to the oil pressure coming up through the passages which are sealed with o-rings, which eventually flatten out and leak into the gasket layers.
They don't have a history of blowing out between cylinders or to atmosphere, though.
Go to the www.cmsnl.com site (or others) and look at the exploded parts views for details about gaskets and o-rings in the installation. There aren't any tricks, other than to be sure that you get the cams timed back in properly again. Take a good look at the cam sprocket marks at TDC before you dismantle everything, to ensure that you understand the relationships of crankshaft marks to camshaft indexing.
I would always suggest that the gasket surfaces of the cylinders and head be checked for flatness.
If the bike has a lot of hard miles on it, you might want to lift the cylinders and hone the bores, installing a fresh set of rings. If the bike has good maintenance low miles and you don't disturb the cylinder block during dis-assembly, then you can just do the head gasket and be done. Once the cylinders come loose from the crankcase, even momentarily, you stand a chance of having a damaged base gasket (oil leak). If you have the time to do it right, pull the whole top end off and replace all the gaskets after checking surfaces for being flat and true.
Folks on a budget have tried using some hi-temp RTV silicone sealant on the outside of the gasket edges, if that is the only area of concern.
I would definitely change the valve stem seals, though, as they are 30 years old and hard as a rock now. It is a lot of extra work and you have to keep track of all the valve shims, so you don't alter the clearances on reassembly. You'll need to check them anyway, as the motor goes back together, to prevent any further problems down the line. Hardened valve stem seals lead to oil smoke/use, especially at idle or during long periods of deceleration (downhills, etc.).
I once replaced a head gasket for a customer, when I was working in a shop, only to discover that the leak reappeared again. The leak was in the center of the motor, in front. Turned out to be a fracture in the top of the cylinder casting where the camchain opening is. I called the customer and we both agreed to JB weld the crack (hairline) and it was fine afterwards. Pretty rare incident, though.
Good luck with the project.
Bill Silver
