Cracked pre-chambers

[JeepSJ]

Well, I got the heads off and cleaned up so that I can install my new head gaskets and studs. I found that 6 of the 8 cups are cracked. None are cracked to the fire ring, but a couple are fairly large. It also appears that all of the cups are either flush or down about a thou.

So, while I have the heads off and I'm waiting for my KL-3900 to get here, should I replace the cups? If so, how do they come out? And, where can I get them (besides the dealer)?

Also found a couple scratches in the #5 bore. If I wasn't in a time crunch to get this thing running (moving to San Diego next month), I'd take the time to get it bored and install a set of 18:1's. I'll just have to run it like this for now. It has a 12 month warranty, so if it has any problems, I can file a warranty claim. I'm going to document the scratches with pictures and send a registered letter to the rebuilder so that there is a record of the problem. But, the scratches may be nothing to worry about. The engine supposedly only has 17K miles, and from the look of the main bearings I'd say that it has less than that.

Sorry for the rant - any opinions on the pre-cups?

[DmaxMaverick]

You will find cracks on a new engine. As long as the cracks don't go into the fire ring, no problem. If you replace them, the new cups will look like the old ones in no time. Wasted time and money to do anything about it. Good luck finding them if you do decide to replace them. Now would be a good time to install new glow plugs (60 G's or Kennedy quick heats, if you haven't already thought of it hint...hint). Cheap insurance.

As far as the cylinder scratches....
It will have no effect on the engine's performance or longevity as long as they are not too bad. Worst case is you might use a little oil between changes. There is a big difference between goring (bad) and scratches. If you are considering overlooking it, then it must not be too bad, not to mention the rebuilder willing to warranty it like so. Get it together and do a compression test. Odds are you won't even know they are there. If you are installing new rings, a hone is in order. When you do a good cross hatch, the scratches might up and leave you alltogether. If you can't measure it with a deapth gage, no sweat.

Don't forget the balancer and crank pulley. When in doubt, REPLACE IT!

Don't worry. Be happy. Sounds pretty good, so far.

[Kennedy]

You might try to take a light hone in the scratched cylinder. Not the proper way to do it, but given the circumstances, it will likely help with ring seal. Sounds like something may have dropped into the cylinder.

Cracks are common as stated above. I've seen some w/o cracks, but seldom find any with serious cracks.

[cruzer]

Just a thought, nows a good time to port match the intake and exhaust ports in tne heads and manifolds.

[JeepSJ]

It looks like I need to replace one, maybe two. I have one that is cracked through the fire ring, and another that is questionable. I guess I won't worry about the others.

The question remains - how do you get them out, and is there a source other than the dealer?

[More Power]

Use a drift through the injector hole to remove the cups.

The GM service manuals state that (and as mentioned above) that as long as the cracks don't cross the compression sealing ring of the head gaskets, you're OK.

The deck height tolerance for the cups is + or - .002". But, it's not hard for a good machinist to get them spot-on, which is better.

Incidentally, it's recommended that the cups be removed when resurfacing the head deck. Then machine the pockets to get the cup deck height correct.

MP

[tom.mcinerney]

JeepSJ--I inquired with Avant Salvage about buying a couple used-good prechambers. He had them. Jamie asked me what were the identification markings on the ones i wanted to match. Some have round dot(s), squared holes, letter "T", etc. I can email foto of two types, if post email address; or just call Diesel Depot....

[JeepSJ]

Thanks, Tom. Jamie still need to send the gear drive that I ordered, so I'll give him a call and see if he can toss a couple in with the shipment. Mine are "diamonds".

[JeepSJ]

More on pre-cups...

Has anyone else noticed that the head gaskets for a 6.5 have metal over the pre-cups? Looking at the gaskets, it appears that the steel that makes up the fire ring on the gasket is extended to completely cover the pre-cups. Could they have designed the gaskets this way to compensate for the cracks? Based on this design, it really doesn't look like cracks extending past the fire ring will cause any problems. I have one pre-cup that is cracked outside of the fire ring - when I inspected the gasket, I can see a mark on the gasket in the steel that covers the pre-cup, but nothing that looks like any type of gasket failure was on the way.

I'm still going to change that cup, but maybe we are worrying for nothing.