Top End rebuild questions

[rider_rob]

I am in the process of replacing my valve head. The old one is to the point that it won't take anymore valve adjustment, the shims aren't that small! So i got the old head off, no problem. Put the replacement on and checked valve clearances. The #3 exhaust valves were sticking open. I messed around and got one of them to start moving again, and am gonna do the same to the other. I had the camshaft in, no chain, and was cranking it to get it to actuate the valve. Suddenly it moved way easier. It broke in half!! So I picked up a set of cams off of eBay. Good deal too. But one question, should they bolt right in or do I need to check anything first? Thanks!

[RoadDogma]

You can check lobe dimensions. The service limits should be in the manual for whatever your application is.

[thatkid]

OUCH

Time to remove the head, you need to check your piston crowns, valves, and camshaft bearing caps for damage, cranking with no cam chain is a BIG NO NO pistons will whack the valves, and as you've discovered can snap camshafts. Valves will definitely be damaged.

Sorry.

EDIT

I'll expand,

If any valve is bent even slightly it will over heat/burn out, possibly cracking the valve seat (steel insert), the valves cool while they are closed, a slight bend will cause less surface area contact between the valve head and the valve seat = less cooling.

Imagine the force require to snap the cam shaft, the piston's are cast aluminium, there could be dents caused when the pistons hit the valves.

When the camshaft snapped, something had to give, the camshaft bearing caps are also cast aluminium.

I've saw this kind of thing many times (timing belts snapping), mainly on taxi diesel engines, these are strongly built sturdy engines compared to the FZR. The norm is new camshaft, new cylinder head (cracked cam bearing caps), new valves, occasionally new pistons, rare 2-3 weeks after repair the bottom ends go (big end bearings) 1 or more big end bearings had been flattened. The amount of damage depends on the engine speed when the belt snaps.

Now that's probably scared the shit outa ya. Sorry but i think you need to be aware of these facts. Hopefully you only have bent/damaged valves.

[rider_rob]

I'm thinking I used the wrong terminology. Let me clarify. When I say 'cranked' I mean that I rotated the camshaft by hand. It wasn't easy, but it was possible. Up until this point the engine ran fine. It's still a strong engine, just didn't have any adjustment left in the valve shims. I appreciate the info, and while I have it all apart, I'm gonna check out all of those things as well.

[thatkid]

I'm thinking I used the wrong terminology. Let me clarify. When I say 'cranked' I mean that I rotated the camshaft by hand. It wasn't easy, but it was possible. Up until this point the engine ran fine. It's still a strong engine, just didn't have any adjustment left in the valve shims. I appreciate the info, and while I have it all apart, I'm gonna check out all of those things as well.

That's a relief, when you said cranked i thought you meant "hitting the start button" "cranked" implies the crankshaft, hence my assumption.

If any pistons where at or close to TDC as you "Rotated" the camshaft, valves would contact the pistons, but any damage will be minimal in comparison, doesn't explain the cam snapping though, I have seen a snapped crankshaft before appeared to be a faulty casting. Strange thing was the engine still ran, just knocky unless the clutch was depressed, the snap was at an angle in between #3 big end, and the centre main, 5 main bearing crank (car engine).

As for the no shim adjustment left, worn valve collars/keepers? will cause the valve spring retainer to rise, pushing the shim cup upwards towards the cam lobes. If it is the keepers the valves would eventually have dropped into the cylinders, that cylinder head is still good hang onto it.

[reelrazor]

That's a relief, when you said cranked i thought you meant "hitting the start button" "cranked" implies the crankshaft, hence my assumption.

If any pistons where at or close to TDC as you "Rotated" the camshaft, valves would contact the pistons, but any damage will be minimal in comparison, doesn't explain the cam snapping though, I have seen a snapped crankshaft before appeared to be a faulty casting. Strange thing was the engine still ran, just knocky unless the clutch was depressed, the snap was at an angle in between #3 big end, and the centre main, 5 main bearing crank (car engine).

As for the no shim adjustment left, worn valve collars/keepers? will cause the valve spring retainer to rise, pushing the shim cup upwards towards the cam lobes. If it is the keepers the valves would eventually have dropped into the cylinders, that cylinder head is still good hang onto it.

I'm pretty sure what he had going on was tulipped valves and/or seat recession...pretty common in earlier generation FZR engines.

I'be pretty distrustful of any head that had valves sticking OPEN. The springs have been compressed for however long it was: first, stored, and second, the head has been removed and they stayed that way. Those springs are probably sacked. The vales are most likely stuck open due to rust and carbon on the stems and the guides will suffer almost immediately if it is made to run.

[thatkid]

I'm pretty sure what he had going on was tulipped valves and/or seat recession...pretty common in earlier generation FZR engines.

didn't know it was a common fault on the FZR. thanks for pointing that out.

[rider_rob]

When I got the head, the valves were not stuck open. Everything looked normal. It was when I was doing the valve shim measurements that I realized that the #3 exhaust valves were sticking. I pulled off the head and camshafts, then sprayed some Seafoam onto the valves and let it soak in overnight. Then I pushed down on the valves to get them to release, and voila! All loosened up. Remounted the head, installed cams. Checked the valves, installed the proper shims, and all is good.


Famous last words.