Topic: Help With Binding Head Cover

[OldSchool_IsCool]

'77 550K US Model

I'm having a REAL struggle fitting the head cover over the camshaft.  When I put the head cover on and tighten the hold down bolts to finger tight, I can turn the engine pretty easily with the kick arm.  The trouble comes in when I torque the cover to spec.  The engine becomes bound up TIGHT! can't move it a bit.  Not like it rotates to a point and stops, it's just plain stuck.  If I relax the bolts, she spins normally again.

I'm just finishing a top end rebuild.  The head cover, camshaft, rockers, valves all are original and unmachined.  There is a new cam chain in her now.  There was no binding problem before I took her apart.  There was a boat load of silicon form-a-gasket between the head and head cover though (yes, a foreshadowing statement for all you literature buffs!).

I've inspected the camshaft & bearing surfaces for any foreign matter that might be causing it to bind, but they are all clean and coated with assembly lube.  The new O-ring for the cover is seating nicely so that can't be it.  Frustrating!

I got the idea to put a strip of PlastiGuage on the tops of the camshaft bearing surfaces and torque her down to see if/which bearing is binding.  I also put a bead of plumber's putty over the cam chain to see if maybe the chain was contacting the cover.  When I removed the cover, I got a bit of a surprise.  Maybe someone here can help me figure this one out.

First, the plumbers putty was undisturbed.  The chain was not binding to the top of the cover.  One PlastiGuage fell off (outside left bearing), so no data on that surface.  The other three had an unusual but consistent pattern.  The left end of the PlastiGuage was pristine.  The right end was smashed to the extreme.  I used GREEN PlastiGuage, so the clearance on the left of each surface was .003 or more and the right was .001, possibly less.  This was consistent on all three bearing surfaces. 

Could I possibly have a warped cover?  I wonder if this explains why a PO gooped up the mating surface with all that silicone.

Any advice or thoughts would be greatly appreciated!

[montana550]

I wonder if someone got carrried away machining the mating surfaces, and perhaps out of square.

[OldSchool_IsCool]

I don't see any machining marks on any of the mating surfaces.  I'm not sure what to do at this point.  I could seek a cover at a boneyard, but no guarantee it would be any better.  I'm going to play with this one a bit to see if there is any way to make it good enough.  May have to invest in some of that silicon goop the PO used! 

[1timduke]

So the silicone was heaped on and set before the cover was torqued down by the P.O.?   Was there a gasket under the silicone?   Are you sure that that is the correct head cover for that model engine?   Maybe they had a mismatch from a different year 550 (possibly 500?, I'm not sure).   My P.O. though blue RTV was a substitute for everything, maybe they all went to the same high school...

-Tim

I've heard that type 2 silicone for bathtubs is pretty tough stuff

[lordmoonpie]

way to check where it's binding is to get some plasticine from a toy shop, roll it thin and push it on the inside of the head cover, bolt down until problem occurs and then take off. You'll either get residue on the engine part that's binding or the plasticine squashed flat in the head. Works a treat to find out where your issue is. I used this to find out where my camchain was fouling the head cover in the camchain tunnel....not a normal fault but I've put a DOHC crank in an SOHC engine so different cam setup altogether.

I'd put money on your having the wrong model head for the rest of the engine...