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I need some tips about the cylinderhead mount on a 76 750 ss
I have new valves and seats ,bore and piston which is tight and correct , all timing mark is set but on my vertical cylinder i only get 6,5 kg comp , i have no oil leaks between cyl-head which i can see anyway , should it be some o ring or gasket between cyl -head or is it metal to metal to keep it thight???
do i need to use the valve paste to get it to a 100% surface??
ps. i have the small o-rings for the oil..
sorry bout the language (swenglish)...
Anders Hakansson
Sweden
Hi Anders,
I just noticed your post and since I have struggled with the vertical cylinder/head joint leaking on my '75 900ss since it was new (back in '77!) I thought I'd add my experiences. Firstly, Steve is almost certainly right, check the valve timing!
You can easily check if the joint is leaking, spray some soapy water on the joint and get somebody to kick away whilst you watch. bubbles = leak. That's the easy part. Apparently the problem is usually caused by the head distorting slightly because the metal is very thin under the exhaust port. Mine distorted in the factory because there was a casting flaw on the head, one of the little vertical fins under the exhaust port was too long and rested on the cylinder top fin and bent the whole head whilst being tightened down. I tried using valve grinding paste and an old cylinder liner to lap in the joint but you need to be very careful because I think the real sealing surface is not the flat one but the vertical spigot joint. It helped a lot, but didn't completely eliminate the leak. The final solution was re-machining the joint by a skilled and experienced specialist (Nigel lacey in the U.K.), an interim fix was some very hi-tech high temperature sealant from Loctite (I don't have the the number to hand , it is bright pink and very expensive!) I hated using it but it lasted a few thousand km , and only I knew it was in there! Anyway, I hope it isn't the joint, let us know how you get on.
cheers
In-Two
In Italy today
'75 900 SS
"don't get behind on your cheating, but don't get ahead either" Cook Nielson, California Hotrod
Anders, you also need to check that there is some clearance between the head and barrel when the head is tightened down. If the engine has lots of miles or if it was raced and the head removed/installed many times the head can distort like In Two has described. What happens is the sealing surface wears into the head and the liner doesn't contact the head all the way around. The face of the head hits the barrel casting usually at the stud holes. Careful skimming of the head and/or barrel around the liner will correct it but remember to sink the recesses for the orings the same amount as was removed so you don't squash them too much.
the problem which tricked me to the o ring thoughts was a previous owner make a cirkel(2mm) cut down on both head and cylinder top for placing a (thin copper?)ring for gasket (same as a place for an o -ring) i have them mounted back as i re checked the surfaces.
Comp is exactly the same now on both cyl
the timing was set correctly
But now i have serious doubt on my ignition but that i have posted in the electrical section.
