Cam Timing - Engine Won't Turn!

[Thorn]

Hi there,

I'm pretty stumped on this one, long story short a few months ago my fazer decided life was too much and gave up the ghost. Ended up with new downpipes, a replacement cylinder head and a rebuild project.

The new cylinder head is bolted down and I'm completely stuck at the cam timing. Everytime I get the engine timed up, it just won't turn, it feels completely locked, I dared to give it a little more pressure once and it slipped off the bottom cam sprocket 

Both guides are in and the cam chain tensioner is in, I've looked at various videos on how to do it on thundercat engines and have read up on the various threads here related to the issue, I have no idea what's going wrong.

I transferred the shims from my old head into the replacement cylinder head as I planned to use my old cams as they were in better condition, but I've tried with both sets of cams with the same problem.

For what its worth, the engine turns fine without the cams in, I have not replaced the camchain (30,000 miles) as I simply don't have the funds at the moment, however I'd say it has a good 10-20k left in it judging by the tensioner position when it came out and how tight the cam chain was.

My next plan is to move onto the unlikely stuff, e.g try it without the guides to see if it's getting caught on them, and try smaller shims, it's worth noting that all the buckets push down freely.

Any ideas? 

[Fazerider]

Have you got the inlet and exhaust cams the right way round?
Having the clearances slightly wrong won't cause the engine to jam.
It must be grossly mistimed if a valve is meeting a piston and, if that's what's happened, heaving on the crankshaft hard enough for the chain to jump could well have bent the valve unless the bottom sprocket was knackered.

[red98]

as FAZERIDER dont force it.....when aligning "t" mark on flywheel make sure the lobes on the cams on no1 cylinder are facing away from each other....that puts the engine at tdc on the firing stroke and not the exhaust stroke......saying that though if it were 180 out it would still turn over........go back and make sure the chain is seated properly on the bottom sprocket and then fit the cams again...its a bit of a fiddle but take your time and nice and gentle 

[Thorn]

Have you got the inlet and exhaust cams the right way round?
Having the clearances slightly wrong won't cause the engine to jam.
It must be grossly mistimed if a valve is meeting a piston and, if that's what's happened, heaving on the crankshaft hard enough for the chain to jump could well have bent the valve unless the bottom sprocket was knackered.

Yup, the cams are clearly marked E and I, it's not the first dohc engine I've timed! 

You're right about the clearances, I tried it today with no shims which made no difference - absolutely locked solid from the start.

It's not mistimed, the valves are nowhere near the pistons. When timing it up, only pistons 1 and 4 are at TDC, whereas the cams are pushing Exhaust 3 and Intake 2 down.

I certainly didn't heave on the crankshaft  it was the lightest of pressure and it jumped, I've verified the valves are straight as I relapped them all when I received the head.

as FAZERIDER dont force it.....when aligning "t" mark on flywheel make sure the lobes on the cams on no1 cylinder are facing away from each other....that puts the engine at tdc on the firing stroke and not the exhaust stroke......saying that though if it were 180 out it would still turn over........go back and make sure the chain is seated properly on the bottom sprocket and then fit the cams again...its a bit of a fiddle but take your time and nice and gentle 

Yup, that's exactly how I've done it, I've had the cams bolted in and out atleast 10 times now trying various things.

The chain is sitting on the bottom sprocket properly, it also rotates with the engine nicely with the cams removed. I tried it again today without the CCT installed. I held the cam chain up at the top, while rotating the engine, with a little pressure (still jammed) the chain rides straight off the two cam sprockets and then rotates freely.

It's definitely the topend that's jammed solid, my only theory at this point is the replacement head is actually warped, I didn't notice anything with the metal rule before I put it on though. I'm going to try again tomorrow with my old head and see if the cams rotate.

I suppose this might be why the head was only £50, with cams, buckets and shims included. For what it's worth, the bike it came off had clearly been burning oil for quite a while!

The bike's been off the road since march, and it's been a fight every step of the way, kind of gives the feeling that it doesn't want to go back on the road 

[unfazed]

Are you using the cam caps from you own cylinder head or the ones that came with the replacement?  The cam caps are machined in situ at the factory and are not interchangable, they have to go back on to exactly the same places they were taken from. Easy to refit them in the wrong place as they are all similiar with just arrows point to the right side.
They could be out of  line enough to prevent the camshafts turning when the cam cap bolts are tightened.
Were the caps loose when you recieved the head, if so they may have been removed and put back incorrectly?

[Thorn]

Are you using the cam caps from you own cylinder head or the ones that came with the replacement?  The cam caps are machined in situ at the factory and are not interchangable, they have to go back on to exactly the same places they were taken from. Easy to refit them in the wrong place as they are all similiar with just arrows point to the right side.
They could be out of  line enough to prevent the camshafts turning when the cam cap bolts are tightened.
Were the caps loose when you recieved the head, if so they may have been removed and put back incorrectly?

Oops, good catch! I've actually been using the caps from the old cylinder head, I didn't realise there would be quite that much of a difference. I'll try the correct cam caps for the head tomorrow before I do anything drastic!

[red98]

oh yes that could be it..i would use the new caps and cams and see if it turns ..try the caps in all positions.if you do end up taking the head off again use a steel rule and some feeler gauges to see if its warped...... ....good luck

[unfazed]

Make sure the punch marks on the right hand side of the cams line up with the punch marks on the caps and the T mark on the rotor lines up with the line where upper and lower crankcases meet at the front of the engine. They should line up exactly with a new cam chain but could be out a few degrees with a worn chain.
Do not turn the engine over without the tensioner in place the chain willl jump the sprockets (even a new new chain will do it)

[Thorn]

So had another go today, used the correct cap caps for the head this time and it turned over like a champ! Had time to get the valve clearances sorted and finish the engine assembly.

Craziest thing I've ever seen to be honest, pretty much means if you buy a replacement head and don't get the cam caps with it you're screwed!

In any case, engine is back together now, props to unfazed for pointing that one out 

[unfazed]

Glad I was able to help, 
Yes, without the cam caps, any overhead cam cylinder head is worthless.
 
 

[Ebme Geek]

This is why the manuals say be careful not to damage a cam cap otherwise you have to get a new head asembly  -  Ooch !

[red98]

thorn...which cams did you use in the end ?

[Thorn]

thorn...which cams did you use in the end ?

I decided to use the cams that came with the replacement head, the difference in wear wasn't significant. I'll refurbish and do a bit of work on the old head at some point so I have a functional spare 

[unfazed]

What happened the original head?
 

[Thorn]

What happened the original head?

Exhaust studs snapped, replacement head was substantially cheaper than getting 6 studs drilled out and replaced.