6.2 rebuild

[thejim662]

Hi Again!
i have an 82 red block 6.2 that im currently rebuilding and need to know a couple of things before i carry on.
Firstly the bores are all in spec but do have a very small ridge on them, so should i rebore 20 thou oversize or leave alone and secondly what pistons are better clevite or silvolite? I also need to know the best amounts of clearance to run for each brand of piston.
Also the heads on the original motor were in pretty poor shape (cracked!) so i found a set of heads from a later motor (84 or 85 i think)
the heads are in good shape except for two exhaust valve seats which are pitted. I have spoken to a shop here in the U.K. that specialises in head rebuilds and they are 100% confident that the seats can be machined out and new inserts can be cryogenically fitted prior to the seats being cut.
Does anybody know of this being done previously and if so did it work okay?
Thanks for the help
Jim

[Robyn]

Hard seats can certainly be fitted with no trouble at all.

As far as a rebore, if the cylinders and pistons are in good shape just rering it.

If you do do an overbore the brands you mentioned are both good replacement parts.
The clearances are usually supplied buy the maker.
If not the engine manual will have the specs.
I beleive GM says .004" on Cyls 1-6 and 7-8 shoud be about .005"
The back two are always fit a tad looser on these engines due to heat issues.

If you use a particular brand of piston, do follow the manufactures specs as every piston can be different depending on how they are made and the materials used in their contruction

Hope this helps

Robyn

[thejim662]

Dear Robyn,
Many thanks for the advice it is much appreciated!
More questions soon!
Jim

[john8662]

If you do do an overbore the brands you mentioned are both good replacement parts.


I have to disagree with the recommendation of Clevite or Silvolite pistons for a rebuild.

The Silvolite pistons will crack and fail prematurely compared to the factory pistons. Most Clevite boxed pistons are Silvolite pistons, some are Mahle, can't tell until you receive them. Cracking Silvolite pistons is accelerated under Turbo useage as well.

Clevite does not manufacture pistons for the 6.2L.

The tried and true pistons for the 6.2 are the Mahle, and (so far) the Sealed Power Pistons.

As far as clearance, in some Clevite boxes, the specifications call for up to .007 of clearance, or adding for the type of use.

Do no exceed .005" cylinder to bore clearance.

The recommended is .004"

The minimum should be no tighter than .0035"

As for boring, if you've got a ring groove on the top of the bore, it will likely need to be overbored, if the specs are close now, it'll have no problem with a .020 overbore (.50mm)

J