Dear gentlemen, gentlewoman,

I've been busy last months getting all the parts for rebuilding my engine (4.0 AJ26 s/c). All parts that wear down are going to be replaced.. Valves, valve seats, crankshaft bearings, some broken pistons, piston rings, all gaskets etc etc.
The bed plate has already been united again to the engine block, with the beautiful Loctite sealant. Now I want to install the pistons, but I've ran into some issues getting the compression piston ring inside the bore.

piston ring type

The rings that I'm using are Mahle original JLM20929 (pic above), but I've tried about everything I can think of, ring upside down, piston upside down into the bore, leading with empty piston, giving it a goodnight kiss, tightening the piston ring compressor until blood came out.. nonetheless, nothing worked. The 2nd piston ring (wiper ring) is the same size as the compression ring and does go in normally. The OD of the compression ring is also the same as the original rings that came out, only the ID is larger.

Has anybody experience with the piston rings that I have getting them inside the engine block? If so, could it be my piston compressor (pic below)?

piston ring compressor

Thank you all!

 

Can you get the ring in by itself? So test fitting it in the cilinder without the piston? On the odd occasion the two ends of the ring touch each other and the ring simply would not fit into the cilinder.

Jeroen

 

Hi Jeroen,

When I dry fit the piston rings they have a visible gap, around 0.4mm.

 

sounds about right, very odd. Only other thing I can think of, is to measure the ring groove inside diameter and depth and compare with the old piston, see if anything differs.

 

Hi Jeroen,

Will try that tonight when I get home from work

 

Hi Jeroen,

I placed the piston ring on the 2nd place (middle) and it does fit within the bore, so that's nice to know.
I'm going to adjust my clamping tool with an angle grinder and see if that will work.

Also, I saw that you're located in Spijk. Greetings from your 'overseas' neighbor in Arkel

 

Hi Jeroen,

So I managed to make it work, my hacky angle grinder job did it's job. I placed the clamping portion closer to the edge by grinding the steel rivets away and moved it all 1 position down, then riveted it back.



As I accidently managed to damage piston number one by trying harder yesterday I will get an replacement one, but number 2 fit in without any effort this way.

 

Where are you getting a replacement piston from? I can’t imagine that’ll be an easy find. Also, is it my imagination or does the top of that #2 cylinder wall look scraped up? I don’t think you can use a hone for that nikasil coating.

 

I know someone who has an engine with grade 2 pistons, got already 3 of them because my piston glands were f'd up.


F'd pistons (all broken metal was still nicely in between like an jigsaw for engineers)

The "scraped up part" is actually an reflection of the thick 20w50 oil that I'm using for assembly

 

Good to hear you managed to make it work. So it was just the clamping tool that was not compressing the rings sufficiently!

Jeroen

 

I never ever use that type piston ring compresser tool anymore. Went and tryed one time tapered adjustable aluminium piston ring compresser tool and never going back. It was so close to broke of 50 yo NOS piston rings that I had to look out for other tools.

https://www.proformparts.com/product...minum-material Like so.

 

Hi Wildcat,

Did you manage to find details on the allowable clearances and tolerances between the piston diameter and the bore diameter?
The engine repair course Doc. states the following:


But if both bore and piston are grade 2 then the piston could be bigger than the bore!! Unless I'm missing something?

If you have the clearance/ tolerance specifications I would love for you to share them please.

 

Hi DJB XJR,

I have the same document as yours, only the original PDF. Eventually, I discovered that the new piston rings available for sale (the mahle ones I showed in the picture) are wider than the original older ones. So I found a scrapped engine from 2001, with grade 2 pistons where the grooves are deeper. That worked like a charm.
I still have the old pistons lying around, I can measure the groove depth for you if you want me to.

Kind regards,
Wildcat

 

Yes... that one provides much better insertion technique.