hacker-pschorr

I'll have to check on that. Last time I looked the 4.7 rings where 75% less than 4.5's.

How much are these JE's pistons you are talking about? The rings are not close to that kind of money. Unless I'm missing something.

BC

Well, when you bore more out, you can then use JE rings for another car if you stay to that size. You have your own "Man" in JE that can order them for you.

918-S

Thanks for the suggestion. I'm over 300 HP now with all the accessories removed and free flow exhaust. There is already an issue with traction as you can imagine.

I have a nice spare 4.7 in the corner just in case I get a wild one.

BTW: Spoke with Tom at 928 International today. He confirmed I would be within the norm to simply install fresh rings into good stock bores. Thanks for all the help and links.

See you on the streets!

mark kibort

i have a set of 4.7 euro pistons, missing 2 (and they are 1st size oversize)

we may have a almost brand new 4.7 euro bottom end for sale. 5000miles on it, 4 partial race weekends. head gasket issue.

mk

danglerb

If you don't bore the block, do you need to do the lapping thing for new rings?

mark kibort

no, if the bores are in good shape, just re ring and put it together. its one of the beautiful things about the alumisil 928 blocks. and, there is very little break in.

if you have to re-bore, or hone to fix scratches, you need to do the lapping process

Mk

Vilhuer

It doesn't hurt to do lapping even without boring to oversize but its not necessary.

Larry Velk

I'm sure the lap process is well mastered by now, but it wasn't trusted with the Vegas of 1971. The Chevy Vega blocks were similar in concept. Chevy had a method for refinishing the bores. When the head gaskets failed, which they did with disarming frequency, the bores would inevitably score. Chevy did not object to a block replacement. Considering how cheap they were on warranty repairs I can only assume they had no faith in the refinishing methods on that alloy at that time. ( A Vega tune-up kit was two front fenders and a short block). The car was much worse than a Pinto, but GM had better payola with the press ( Vega had a gas tank explosion refit kit also).

Vilhuer

I think problem in Vega engine was that silicon crystals were not spread evenly in block casting becuase of gravitys effect on material while in liquid form. Without doing something silicon distribution was uneven. Both Cosworth and Mahle (maker of 928 block) solved this problem. Cosworth by rotating casting upside down while it was cooling and Mahle by placing heater elements inside casting to control temperature on cooldown. In Vega there weren't correct amount of silicon in block walls to lapping to be effective as Chevy didn't think about this problem. At least not at first and damage had been done creating bad reputation for the engine.

Namvet

Just get a first class valve job and check the Guide clearances. A compression check , (warm), before and after should suffice.
Porsches are sealed...for a long time.

Namvet

..and please don't compare a Porsche to a Vega!

tv

Someone posted a link here to a 100 page pdf complete with pics of the whole process put out by Kolbenschimdt. It is interesting.