Cylinder Advise

[txhokie4life]

Got a set of 102mm Mahle Jugs from my 3.8L tear down.
I do not know the complete history. The Ross pistons that it came with
are out of spec -- there is 0.0055-0.008" clearance, and some evidence of
piston skirt scuffing. The pistons are becoming paper weights.

I do know the heads were "melted", but they have been reflowed and rebuilt.

Trying to decide the best course of action with the Jugs.

Here are the measurements off of a 4.015" bore size. Ovality within 0.0005, taper within 0.0002-0.0003, max-bore delta among all pistons is 0.0006.



I have one jug that has some plating that is flaking off -- all others look fine.



What should I do with these jugs...... looking to re-build up the 3.8 race/track engine.

If I need to machine the jugs.... I could consider going to 4.0L as that
fits within my class.

I've considered going to nickies and dispose of these jugs -- but the cost seems pretty high if these are useable.

thanks,

mike

[Steve@Rennsport]

Mike,

Are your cylinders the 107m or 109mm spigot versions?

[txhokie4life]

Originally Posted by Steve@Rennsport

Mike,

Are your cylinders the 107m or 109mm spigot versions?

Case opening is 4.21" which I believe is 107mm.

Mike

[Steve@Rennsport]

Thanks.

Its quite common to see out-of-spec ovality in these thin-wall cylinders and one reason why I don't use nor recommend them. They simply will not stay round in service.

You can have your current ones honed and replated (I'd recommend US Chrome) back to standard, however these will not stay round and ring sealing suffers for this.

I'd recommend either buying new Mahle thick-wall RSR P/C's if your piston ring lands are worn to spec, or using Nickie's if they are still OK. Naturally, the case will need to be machined for these.

I would not go bigger than 103mm no matter what you decide on.

[txhokie4life]

Thanks for you input Steve.

I've been told that these measurements are fine:
Ovality within 0.0005, taper within 0.0002-0.0003, max-bore delta among all pistons is 0.0006.

Now if you claim that the bore size is too large -- 4.015 spec to 4.016-4.017, then I get that.

I've looked around, but I haven't seen any tolerance specs.

The pistons are out of spec and I was expecting to change to new pistons.

thanks,

Mike

[KTL]

That's a lotta clearance for sure! That's a lot of plating loss too.

Looks like you're measuring them with a 0.0005" resolution dial indicator. Really need to use a 0.0001" indicator to get good solid measurements. I found using a 0.0005" indicator that I wasn't 100% confident in my measurements when you start to calculate what your true bores and clearances are.

Just my opinion. Good luck with your rebuild

[Steve@Rennsport]

Mike,

Without measuring everything for myself, I'm unable to offer anything constructive,..

It does look like these need to be re-plated, should you decide to keep them in service however I just cannot say for sure. Ovality just within .0005 isn't great IMHO as this get reflected in ring sealing. Given that P to C clearance should be no more than .0002-.00025 with Mahle's, you really need ovality within .0002 to minimize blowby.

Kevin's tip about measuring resolution is really spot-on. For any useful values, you need more accurate & precise data.

[txhokie4life]

Just circling around : Picked up a more accurate gauge and had my friend redo his measurements.

I think this is within spec, but some of the cylinders may need replateing.

Recommendations?

thanks,

Mike