moparguy

Got the engine out and the head off the project truck (130k, dusted rings)and the cylinders look ok, no scratches or grooves in the cyl. walls, however all the factory hone marks are gone. I was hoping the dusting from a bad airfilter had only taken out the rings.

I've pulled the pistons, but haven't comeup with a inside dia. mike to check bore dia. and taper (may have to resort to feeler gauge to check piston to cylinder wall clearance). However the poor abused top piston ring has .077 end gap 2" down in #1 cylinder. At the bottom of the cylinder, below the wear area, it's .073.

Question to the group, how much wear is too much for a hone/ring job.

Remember, not trying to build a ProStock engine, just a farm rig.

Thanks, RR

jaconst

130k is TOTAL MILES seems like not right I would think 1.3 million

jogl

I recently did a "Berlin rebuild" (rings and take glaze off the cylinder walls, and I took out the ring ridge) on one of my D24 engines (2.4 liter VW diesel out of a Volvo).

The cylinder walls looked bad with the ring ridge. The local engine machine shop measured bore for me and the worst was .011 over and .007 out of round. He said I should bore it but I didn't want to invest that kind of money so I just cleaned it up as mentioned.

The interesting part was the rings. The top rings were wore down to almost razor blade thickness in spots. The coking in behind them must have kept pushing them out. On the worst one the ring end gap was 5/8"!!! It is amazing that the engine ran like that, but I saw it.

Anyway, after the cheapy rebuild the engine ran fine, but it does not have a lot of hours on it yet. If that were my truck I would just try a cylinder clean up and some rings. If it does not work out take it apart again and spend the big bucks at the machine shop. Based on my limited experience I doubt that your cylinders are wore much, the rings made the sacrifice for the dirt.

Good Day, JP.

berner

My Cd service manual says to measure the bore 1" and 4.5" down the cylinder. Taper should be < 3 thou. If your doing it by measuring ring gap (smart idea) you'll have to crunch some #'s to get the taper. The difference between the min dimension on pistons and max on cylinders stated in the CD specs is 11.5 thou.

If you're replacing pistons, there are three different grades depending on the distance from the top of the pin bore to the top of the piston. The # should be stamped on the top. You have to replace them with the same grade.

All that being said, I've rebuilt small block Chevy's that have had 10 thou taper and they ran fine. How long the top ring will last is anybody's guess. The most important thing is to use a ridge reamer and get the ridge out of the cylinder. It doesn't take very long for the top ring to disintegrate if it's slamming into a ridge every time the piston comes up.

russ300h

The general rule of thumb is .015 to .017 taper as max allowable in a gas engine. I would second the .0115 as sounding reasonable on a diesel. The more the pistons rock in the bore, the less the rings will seal. This would be much more critical in a diesel with twice the compression plus a turbo boost.

Checking the piston clearance will not give you the reading you need. You need to check the bore with the piston removed and a gauge. Check the difference between top and bottom to determine if you can get by with just rings.