Ad0911

I have reached the point to do some desicion making. Am I going to rering the pistons or not?

I measured the clearance of the rings in the grooves. It is tighter than 0.10 mm top ring and second ring. I haven't measured the ring gap yet because my ring compressor is not larege enough, have to get myself a bigger one first.

Sedond decision is if I am going to fit new big end bearings. Engine has 90,000 mls on it. See pictures. I really don't feel like changing the bearings because on this piston I don't see any wear to speak of. Other pistons are still in the block.

What do you think?

GlenL

I suspect you know this but rings are gapped by sticking them into the bores.

Did you do a compression test before the tear-down?

GregBBRD

Those bearings have enough wear and debris in them, that I would not use them.

I'd also be looking at the rest of the bearings, if I had those on one rod.


However, keep in mind:

1. I do repairs that I warranty and never want to think about, ever again. I expect every engine and transmission I assemble to last another 100,000 miles....minimum.

2. In my mind, bearings, rings, gaskets, etc. are disposable wear items in an engine and they have served their purpose, if they ran 90,000 miles.

3. Rings and bearing are "chump change" compared to the cost of the "hard" engine parts.

Ad0911

I measured the ring gaps of the first and second rings and did the ring groove measurement again with a new feeler gauge. The old one didn't have the 0,05 mm gauge anymore. The ring groove is an honest 0,05 mm, 0,010 won't go in.

I took out the first and second ring and put them 15 mm and 20 mm from the top, which seems about the top dead centre. At that height the top ring has 0,70 mm ring gap and the second ring has o,50 mm ring gap. This definitely exceeds the tolerances, but will new rings give me back the 0,20 - 0,40 mm ring gap? And I really hate to have the engine rebored etc to oversize and fit new pistons etc because it was just running to d.... good for that. Oil pressure was always very good, immediately after startup.

Can I do with rering and new conrod bearings? will that improve the engine? I already had the heads overhauled professionelly so that should be good now.

FredR

Ad,

Quite some time since I did a ring gap check but when I did I always measured mid bore, bottom and as you did at the top of stroke to check if there is any differential wear in the bore itself- piston velocity being highest mid stroke.

In the case of a 928 engine that is something technically beyond the dinosaur engines I have worked on years past, I do not know what one typically might expect to see at your stage in the life cycle but if you measure numbers that take it outside the specified allowable range surely it makes sense to replace now whilst everything is apart?

I do not change anything I do not have to and will run things to the point where I feel "enough is enough" to economise [see my brake thread] but I do so knowing that I can get at the parts concerned with minimal effort any time I want and monitor their condition from time to time.

With the engine it is a whole different ball game and the last thing you want or need to do is trash the block given to do what you have done must take at least 150 hours of effort [double that in my case].

Is the crank still in the block [cradle not disturbed]? If you have followed Greg's engine posts you will not a recent comment that he is seeing a notable increase in damage to the front main bearing that attributes to the engine damper not its job because of the state of the rubber that age hardens. He offers a new damper kit using an adapter to his specification and an after market damper.

Just highlighting the above for your awareness. I also understand that the stock dampers can be rebuilt but no clue as to how good such work may [or may not] be.

Rgds

Fred

GlenL

This, my friend, is a question you'll have to answer for yourself.

The first test shows the rings are worn. These engines have connecting rod bearing problems, too.

The first question leads to a few more:

How will the engine be used?
Do you want to spend the money for parts?
Can you do this yourself or is it a commercial job?
What is your confidence in doing it yourself?

I've done a few engines and I'm still nervous when putting those rings in. Not a perfect track record of getting them into the bores correctly. Bearings are farily easy.

I do expect that new rings will have a better gap. The wide gap indicates that they're worn. Besides the blow-by through the slot what you're really hoping is the new rings have more tension to hold them against the walls.

Personally, I'd do the rings and conrod bearings. I'd be tempted to leave the crank alone unless it's an automatic and then I'd check for thrust bearing wear.