Help with 4.6 stroker rebuild after failed cam gear

[kkchevy3]

So the cam gear is shot and has eaten up my distributor gear. Im guessing about 20,000 miles since i built it. I tore the motor down yesterday and found some other things that might need some attention. My friend that builds engines for a living did it so i forget most of the specs but from what i remember its a 91 block, 7120 head, 4.2 crank, 4.0 rods, .030 over custom pistions?, comp cams 68-232-4, stock oil pump. So a couple of questions. While i have it apart should can i do anything to it that will help the pinging issue i have in the summer on the highway. Its not terrible but Id like to try and fix it. Another thing is the timing set looks shot. Heavy duty replacement? Also one of the exhaust valves looks rusty while all the others are white. And anything else you guys think i should check while i have it apart? Also cam suggestions?

[kkchevy3]

Some more pictures

[kkchevy3]

Some more pictures

[SIXPAK]

When used to run timing chains on the race jeep we used to cut a small slot in the front of the cam gear sprocket. This slot would start at the oil hole in the cam gear and extend just pass the washer behind the cam gear bolt. This allows oil to be directly put on the chain. Just an Idea.

[SilverXJ]

The timing set is shot, but its just a stock style replacement. Get a dual roller. Either Cloyes or JP Performance. That is a lot of wear for 20k miles.

That one cylinder looks like it has had a coolant leak. Possible bad head gasket. I would have the head magnafluxed and checked for flatness. Also, you need to replace the spark plugs. What is that green stuff on the head? Did the rest of the oil look like that?

As for reducing ping you can polish the combustion chamber and the dish on the pistons. You could have the pistons dished as well, but I don't know if it can be done with the rods still on the pistons.

Those pistons don't look custom. They look like stock cast pistons.

[kkchevy3]

green stuff is some nasty coolant. and it just leaked when i pulled the head off i think. He might have not replaced the timing chain, i vaguely remember him saying it looked fine. they have .030 stamped into the top of the pistons.

[SilverXJ]

That green stuff looks like coolant mixed with oil, which is why I asked about it. Oil and coolant will be present on the head gasket when removing it, but shouldn't be mixed like that. I'm still leaning toward a coolant leak from the coolant/oil mix, the deposits in the #6 combustion chamber and the rust on that exhaust valve. The 30 on the pistons could be the over bore size, but I have also seen "50" on stock pistons, so it could mean nothing.

[Cheromaniac]

You certainly have two serious issues going on here:

1. Severely worn cam sprocket teeth. They look like they've been eaten into by the chain so that suggests there's inadequate lubrication. Oil should drain back from a hole in the front of the block to the back of the timing set so make sure it isn't blocked. The chain also looks like it's overly stretched. This is how the chain should look:



As the others said, get a Cloyes dual roller timing set as a replacement.

2. Coolant leak into no.6 cylinder. The head gasket looks fine so something else is causing this i.e. warped head, cracked head, or cracked cylinder wall. You'll need to take the head and block to a machine shop to check the deck surfaces for flatness and have them magnafluxed for cracks.

[SilverXJ]

What about the possibility that something in the cam or distributor was binding up, causing extra drag on the timing chain? I'd lean toward the distributor seeing as how that gear is chewed up... Or maybe just a general lack of lubrication. What do your rocker arms and pushrod ends look like?

[kkchevy3]

my engine builder said he thinks the cam is walking back and forth causing the distributor gear to fail and all the excessive wear with the timing chain stuff.

[Retlaw01XJ]

my engine builder said he thinks the cam is walking back and forth causing the distributor gear to fail and all the excessive wear with the timing chain stuff.

I'm new to Jeeps but that appears to be a problem that's been reported a few times.
The solution from Chrysler was a cam-retention plate. Too bad performance cams don't use that method.
For those of us using an older cam or an aftermarket cam, the solution could be a solid pin, not spring-loaded. It would limit the cam movement to 0.005" to ???.
But would a solid pin wear the timing cover and end play would increase over time?

[Retlaw01XJ]

As for reducing ping you can polish the combustion chamber and the dish on the pistons. You could have the pistons dished as well,

Right. Another cause could be a lean fuel/air mixture..... that will cause detonation as well. Are you running larger injectors?

[kkchevy3]

Yes running larger injectors. He mentioned making a custom button setup out of derlin . Does anyone know if this has been done before?

[SilverXJ]

Derlin would be good, however it is fairly soft and there really isn't much room to fit anything much larger than the pin. So, the load won't be distributed that much on the soft material. Eliminating that goofy factory spring setup is a good idea. I just used a steel bearing that fit in the hole perfectly. When you have that kind of interface you want dissimilar metals rubbing against each other. The cover is fairly soft aluminum/magnesium alloy (not really sure which one), so you don't want something soft such as bronze or aluminum rubbing against it.

I had put some serious though into making a more substantial cam button using something similar to a roller button used on a Chevy. I would have had to cut a hole in the cover and extend the cover in that area a bit and use a different cam bolt to make it work. However while I was sketching out the layout the engine was still on the stand. I realized at one point that I would have a problem as the serpentine belt rides directly in front of the cam, so the plans were scrapped. I had forgotten that at first because I was looking at the TJ's serpentine belt configuration and forgotten what mine was like.

Does your machinist have any idea what would cause the cam to move though?

[Cheromaniac]

Eliminating that goofy factory spring setup is a good idea.

Seems to work fine on stock 4.0 engines for 300+k miles so I don't think that's the issue here.