Camshaft shifted horizontally

[kriszyp]

I am looking for some advice on what appears to be an issue with my camshaft shifting horizontally in my Mercruiser 3.0 engine (GM 140). The observed issue was sudden power loss and a sharp ticking sound. I have isolated the ticking to the exhaust value on cylinder two. Watching the rocker arms, I have observed that that rocker (in a slow motion video, which I could share, but is larger) is rocking/dipping/opening twice per cycle. I believe what is happening is that somehow the camshaft seems to have shifted horizontally/back about a 3/8 of an inch, such that now the adjacent fuel pump cam lobe is striking and raising the lifter (during the compression stroke). You can see in the photos that the cam lobe is not centered in the lifter hole, rather the cam lobe edge is almost centered (and I can feel/see the fuel pump cam lobe on the edge of that hole). I think I can also see the effect of it on the bottom of the lifters, showing a wear/grinding outer edge on the lifter bottom. Has anyone ever see a camshaft shift (horizontally, not rotationally) like this? And what would cause this, and how would it be fixed? Is it some type of camshaft or bearing failure, or did it possibly becoming loose from the timing gear?

This was preceded by an issue with the impeller/water pump, so the engine has seen some recent potentially high heat. Could that possibly have led to bolt loosening (on the timing gear)? It seems like the next step would be to remove the pulleys/flywheel, and remove the timing gear cover to see if there is bolt loose or some other type of misalignment of the timing gear. Does that make sense? Or is it more likely that there is a spacer near the back of the engine that has broken? Or a cam bearing issue? And is this evidence of a likely onslaught of other failures from overheating (I am not sure how hot it got, or if that is related at all).

Anyway, certainly appreciate any help or suggestions (and what tools needed, guess I need a flywheel puller possibly). Thank you!

 

[Scott Danforth]

the cam keeper plate fasteners could have came loose and the cam could walk forward about 1/4". however it would leave carnage in the timing gear area.

pull the motor, pull the pan, pull the timing cover and look.

only thing needed is regular hand tools and a harmonic damper puller.

 

[alldodge]

have observed that that rocker is rocking/dipping/opening twice per cycle

engine has seen some recent potentially high heat

My thought is there might be a valve lifter and or valve stem issue. Might be as simple as a valve sticking and not fully retracting back into the seat.

 

[kriszyp]

Thank you for the suggestions. One thing to note is the camshaft appears to have shifted towards the back of the engine, not towards the front. I am not sure if the cam keeper plate holds it from moving back or forward (or both)?

 

[Maclin]

First thoughts were that maybe the lifter hole is offset some by design so the cam lobe movement will tend to move the lifter around to keep the wear even, but that pic shows too much offset.

 

[kenny nunez]

I had a boat come to my shop with the same problem.
Plan “A”
This is how I fixed the problem. Removed the timing cover and the fuel pump. With a suitable flat bar against the fuel pump lobe to hold the cam forward and an assistant with a socket to fit against the core of the cam gear and a hammer drive the gear back in place. Now to prevent the gear from slipping drill and tap a #10 x32 through the cam gear and in to the cam shaft at an angle,being careful to keep any drill chips from falling into the oil pan, install a #10x32 Allen set screw deep enough to bottom in the cam body with Locktite. Replace the timing cover seal, timing cover gasket, and with a good grade of RTV carefully reinstall the timing cover and related parts. Go boating.
Plan “B”, remove the engine, remove the pan and timing cover, fuel pump, distributor, lifter cover and lifters. Buy a new cam, lifters and gear, with related gaskets. Get the new cam gear pressed on and reverse the process. If you just replace the cam gear that may also get you by but be sure to keep the lifters in order. I do not think just driving the gear back on if do plan “B” will work, the gear will probably move again.
The choice is yours
When I gave the customer the estimate between A&B he went the “A” route. The boat went home the same day.

 

[kriszyp]

Thank you so much for the help! Getting busy on it...

 

[kenny nunez]

If you are going the plan”A” route, be careful not to knock the rear cam plug out the back of the engine. Good luck

 

[kriszyp]

I thought I would follow up with this, and share a few pictures of the repair process of "Plan A" for posterity and anyone else that reads this. First, thank you so much for the help and directions, everything seems to be working great now!

I took off the timing/cam gear cover, and indeed it was shifted. I measured about 5mm. Less than I thought, but still enough to hit the fourth valve lobe and throw the distributor timing off pretty badly a couple times. I attached a few photos of the camgear shifted, realigning it with a wrench on the fuel pump lobe, and drilling/threading a bolt through the cam gear into the camshaft.

A couple challenges: My bolt was a little too close to the edge of the cam gear, so I had to expand the beginning of the hole so the allen bolt (M5 in my case) would be almost completely inset, so it would not stick out and rub against the cover. Make sure drill a hole as tight as possible against the cam gear. Also, Re-installing the timing gear cover was tricky, the first time I ended up folding/wrinkling the oil pan gasket and it leaked oil. I tried again, cutting off the little nubs on the gasket that were intended for vertical oil pan installation (since the gear cover comes back on horizontally), and using even more RTV, and seemed to seal well.

I am now on step 6, "Go Boating", and enjoying it! Thanks again!

 

[kenny nunez]

Good job. Sometimes we have to forget what the service manual would say and “wing it”. I always had the best results using RTV to reseal the lower part of the timing cover to the pan. Thanks for the photos.