M20b25 cam binding issue

[2ohoh2]

So I ran into this problem and I can't figure out what is going on, hoping someone can give some insight.

I bought a M20B25 motor with a bad head, bought a refurbished 885 head. When I got the refurbished head I was able to turn the cam (off the block) using a socket wrench on the cam pulley bolt. I set the rocker gaps off the block, installed the head, and then tried to get the cam to top dead center by using a socket wrench on the cam pulley bolt again and it wouldn't move. I know this is an interference motor and I made sure that the pistons were down on the cylinders that the valves were open in. I also put a wrench on the crank and rotated it slowly in both directions until I felt it just come into contact with a valve, then split the difference between the two contact positions and tried moving the cam again, lots of resistance and no movement.

I followed the head bolt tightening sequence shown here, http://www.rtsauto.com/the-art-of-bolt-tightening/

22 ft.lb, 90degrees, 90degrees, in order

I decided to pull the head back off and check the head and block for flatness and could not get a .004" feeler gauge under my straight edge anywhere on either surface.

This whole thing has left me, and everyone I've asked about it confused, and I was hoping someone here might have some insight I have overlooked. Let me know your hypotheses and ask any questions that I may have not addressed.

Thanks in advance.

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[2ohoh2]

Forgot to mention that once the head was removed I could rotate the cam again with the socket wrench

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[digger]

Does the fully assembled head rotate off the block ? Seems like it does.

Then you either have valves touching pistons or the act of torquing head is inducing twist or other deformation on the head that is adding friction

Try with head bolts just nipped up a tad

[2ohoh2]

yeah, the assembly rotates off the block.

Are you suggesting that I try rotating it after I put a little torque on the bolts, like at 22 ft.lbs? The thing I want to avoid is putting it on again and having it do the same thing, I want to figure out the issue before I put it back on. I'd be on to the third set of head bolts and gaskets at that point... should have just bought ARP studs and a multilayer steel gasket the first time :/

[digger]

Not even that much to start. Then do it in small increments checking after each stage . Use a set of bolts and the gasket that you've used before as you're only testing.

[jeffnhiscars]

You should line up the timing marks on both the crank and head before you install the head. Then there should be no trial and error rotating. Torque head and install the timing belt without rotating anything.

[2ohoh2]

You should line up the timing marks on both the crank and head before you install the head. Then there should be no trial and error rotating. Torque head and install the timing belt without rotating anything.

Yeah, I overlooked this in my rush to put the head on the first time, but shouldn't that not make a difference? If the pistons were down in the cylinders that valves were open in then they shouldn't interfere... I could rotate the crank freely about 180 degrees with the head on before coming into light contact with valves, i split the difference between contacts and then tried to move the cam and it wouldn't move (I put a lot of force on it too). I understand the theory of putting it on aligned, but if there was that much tension without a valve in contact with a piston couldn't I have done some damage buy trying to start it after and not having the cam move (possibly having a piston then collide with a stationary valve?)

[digger]

did you try and start it?

[Andre3127]

did you try and start it?

If he puts a timing belt on the engine and starts it if the cam is binding, he will probably score or gall the daylights out of a cam bearing, which will require a replacement head.

[digger]

If he puts a timing belt on the engine and starts it if the cam is binding, he will probably score or gall the daylights out of a cam bearing, which will require a replacement head.

did i tell him to try? no

he said "couldn't I have done some damage buy trying to start it" so i asked if he actually did or if he was hypothetically speaking

[2ohoh2]

I got some good advice from a very knowledgeable member here and I think what may have happened is the place I got the refurbished head from may not have greased the cam properly and it may not be totally flat. I'm going to pull the cam and re grease it and also take it to be checked for flatness and pressure tested. I'll get back to you guys when I put it back on.

Thanks for all the responses. I do appreciate the feedback

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[digger]

I fail to see how that magically starts happening only when it's on the block bolted down. For sure people not correcting a warped head and cam tunnel properly is an issue not a lube issue though.

When you adjust valves off the block and bolt it into the block then things certainly do move around that throw clearances off that's a composition gasket for you. So if the cam tunnel is warped then the cam to cam bearing clearance is not uniform and bolting it on might cause it to dflect bind just that nit more so as the cam deflects.

I'd be inclined to check valve sealing while it's apart as you may have tagged one too hard when you used them as some kind of limit stop. and also a proper check of flatness, 0.004" is not a good number for a refurbished head

[jeffnhiscars]

Yeah, I overlooked this in my rush to put the head on the first time, but shouldn't that not make a difference? If the pistons were down in the cylinders that valves were open in then they shouldn't interfere... I could rotate the crank freely about 180 degrees with the head on before coming into light contact with valves, i split the difference between contacts and then tried to move the cam and it wouldn't move (I put a lot of force on it too). I understand the theory of putting it on aligned, but if there was that much tension without a valve in contact with a piston couldn't I have done some damage buy trying to start it after and not having the cam move (possibly having a piston then collide with a stationary valve?)

Refurb or not SOP is to verify cam rotation without valve tension. With the valves tensioned its actually not that easy to turn the cam without some leverage so I wouldnt go by that and even with "the pistons down" a) you could still be out 180 degrees and b) why would you want to ever "split the difference" when theres a well established procedure for reinstalling heads ?

Im not saying you did any damage but it seems to be more complicated than it had to be