Head gasket replacement

[jhornsby3]

Hey All,

After I got everything apart and cleaned, I found that the pre cups all have small cracks in them. Before the gaskets went I was getting great milage at 19.6mpg and everything was nice and smooth. Should these be replaced or are they ok?

Thanks,

John

[Robyn]

John

The cracks usually start at the port mouth and then extend back towards the outer edge of the precup.

GM says (In the service book) that the cracks should be no more than 3/16" long before rejecting the cup.

The usual basis for rejection is "How close" the cracks are to the fire ring on the head gasket.

A crack that extends up to or beyond the fire ring is a NO NO.

If there is a decent amount of distance between the end of the crack and the fire ring, go ahead and reuse the cups.

If they are close, replace them.

If a crack goes under the ring, the gasket will fail.

Also, if the cracks show signs of "Chiping" (pieces breaking out) replace the cup.

A chunk of precup falling out could spell "Game over"

The cups are easily removed with an aluminum or copper rod 1/2" to 5/8" diameter through the injector hole and tap with a hammer.

Clean the register fit in the head very well and install the new cups.

Cups must be from just flush to no more than .002" above the head surface.
The cup must NOT sit below the head surface.

The cups may fit snug or they may be just a slip fit.

If the cups try to fall out when the head is turned over, use a round nose punch and stake the head right alongside the cup in 3 equal spaced spots right close to the cup.

DO NOT USE a sharp center punch "Round nose" maybe 1/8"-3/16 radius
Do not try to stake the cup, stake the head. This does not take much, just a little small "Dimple"

Do this with the cups in place and seated well.

I have had to do this on several heads over the years.

Cups are available from GM but they are $$$$$$$$$$$$$

DO NOT use afternarket cups as they do not fit correctly.
****** These can be used but it takes special tools usually *****

If you end up needing a few cups, call John over at Advanced diesel in Newberg.

He usually has some fine used parts on the shelf.


Robyn

[jhornsby3]

none are to the fire ring on the one head. I have yet to get time to look at anything else due to long work hours and that pesky commute. The 18 hours a day spent on "The Man" sure can take from the wrenching time. I'll get to check the other head tomarrow and see what is happening. Thanks for the tip on John. I have his cell number here some place and can call him if needed. He's been a great life line and I feel I need to buy something soon from him.

Thanks Robyn,

John

[Robyn]

John is great people and will help if he can.

Good luck with the 6.5

Robyn

[jhornsby3]

Thanks Robyn.

Upon cleaning and looking close, both heads are cracked between the valves and the pre cups on the pass head are beyond specs for the cracks. So now am looking for two heads that are good. Now to find them and sell some guns to pay for them. So much for driving ti to work on tuesday. Or anytime in the near future. Off to go bag and tag as you say. Need to clean up some floor space in the shop.

And I do have a call in to John

[6.5TDTahoe]

I have a set of very low mileage,non trauma affected heads. From a 2000 or 2001 warranty engine. Complete as removed with pre cups. Maybe you could use them.

[jhornsby3]

PM sent Thank you