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Theres problem with machining cylinder heads for gaskets and reusing existing old style cylinders. When time will come to replace cyls/pistones because of wear - you'll have to pay for set of new cyl heads.
New c/p sets are new style and will not work with groove in cyl head.
That way is maybe good for quick sale, but not for keeper car
I still think that the best procedure to deal with oil leaks between the tops of the cylinders and the heads is to simply machine the heads flat (to get rid of any warpage) then mate them together, without machining a groove for a gasket in the top of the cylinder.
Theres problem with machining cylinder heads for gaskets and reusing existing old style cylinders. When time will come to replace cyls/pistones because of wear - you'll have to pay for set of new cyl heads.
New c/p sets are new style and will not work with groove in cyl head.
Not the way we do it. The new design P/C's work just fine with the current heads.
Machined for 993 ring seal heads show up on ebay and craiglist pretty often - they all have groove for 993 ring and usually melted towards chamber side.
Guys, keep in mind here that most of us don't need the head gasket. Not to take anything away from Steve and the guys at rennsport, cuz when my heads need to be done again, they will receive my heads to be done...again...
But. If you are dripping oil out of the upper cylinder when the motor is cold, that's not necessarily saying you have a compression leak when the engine is hot. Most of the early heads, once the motor is hot, seal back up. So before going down the very expensive road of a top end build solely because you see a drip where there shouldn't really be one...have a proper leakdown done, with the engine hot. If you find you have a compression issue where the heads and cylinders meet, then have at it, and if you want to do the gasket machining, have at that too.
We resolved my issues without machining the heads for the gasket and I am bone dry still, 45k later. There is a lot behind all this...but I'm just throwing it out there since many jump to an expensive repair and get little to no gain beyond a missing drip on the floor...and for me, not dripping on my floor isn't worth 10,000 dollars. (Or more)
Machined for 993 ring seal heads show up on ebay and craiglist pretty often - they all have groove for 993 ring and usually melted towards chamber side.
If they melted, thats a totally different problem and unrelated to the machining modifications.
Originally Posted by Steve Weiner-Rennsport Systems
I'm unaware of anyone else doing this, but there sure could be others.
Having done well over a hundred sets of these early heads now, I'm pretty confident that its a sound solution and a good alternative to buying the late-model ones (with gaskets) when the current ones are still in excellent condition.
Hi Steve - Just out of interest, when is a set of cylinders too far worn to reuse?
If they measure up at spot on 100.0mm i/dia when new, and are no use at maybe 100.1mm i/dia? What type of measurement would they be before you would recommend replacement or re-coating instead of re-using?
I realise that there are other factors such as ovality or scoring, grooving etc to consider but for the sake of argument say that it's based on purely measuring the i/dia?
Hi Steve - Just out of interest, when is a set of cylinders too far worn to reuse?
If they measure up at spot on 100.0mm i/dia when new, and are no use at maybe 100.1mm i/dia? What type of measurement would they be before you would recommend replacement or re-coating instead of re-using?
I realise that there are other factors such as ovality or scoring, grooving etc to consider but for the sake of argument say that it's based on purely measuring the i/dia?
2) Piston condition: ring land wear and skirt dimensions
The biggest area of wear is at the top ring lands and when those are at or below spec, its time for new P/C's since Mahle doesn't sell individual pistons; only as sets. Generally speaking, the cylinders last a LONG time.
Before we do any work to the heads & cylinders, we check the pistons very carefully to ensure they are well within spec so everything will last a long time.
Originally Posted by Steve Weiner-Rennsport Systems
Before we do any work to the heads & cylinders, we check the pistons very carefully to ensure they are well within spec so everything will last a long time.
Thanks Steve, good answer as always
So assuming taper, ovality, Nikasil, ring land and skirt are ok, what is the spec figure for actual measurements?
I guess I'm asking if there is a factory or specialist recommended tolerance e.g. 100.0 - 100.05 passes inspection with less than .02 taper whereas 100.05 and larger or more than .05 taper or ovality it would not be recommended to re-use?
If this is IP or not something that is not really public information then no worries, I'm only asking as it's useful info for us poor folks on a limited budget looking to re-use or replace with used cylinders rather than fork out for replacements where possible.
My 1990 heads were machined to accept the gasket. Unfortunately upon tear down I can see that two cylinder edges have chips. I'm not sure if my heads were machined as well. I hope not as the the options get very expensive if I need all new cylinders, pistons and heads.
If the heads were machined, at a minimum I may need to source used cylinders and pistons of the right group and machine them to accept sealing gaskets.
EDIT: I'm an idiot. I didn't notice they were 930 heads when the secretary showed them to me as "mine" while the builder was away. I got my motor today, saw pictures, and they look exactly like above. Can't wait to drive this thing.
Interesting thread.
Can anyone with experience tell me what setup these heads are machined for?
02-09-2016, 12:39 PM
