I am replacing the piston rings (standard size) on my 1977 300D and would like to know which brand is better: Deves, Goetze, Mahle, or another brand? An independent M-B technician (with factory training and worked at a M-B dealership before opening his own shop) told me that the rings on the early 300D's were not the best and could have been better.

Thanks,
Tom

__________________
America: Land of the Free!

1977 300D: 300,000+ miles

American Honda: Factory Trained Technician & Honor Grad.
Formerly:
Shop Foreman;
Technical Advisor to Am. Honda;
Supervisor of Maintenance largest tree care co. in US for offices in Tex.

Goetz brand were recommended to me by a top notch automotive machinist that has rebuilt a number of these engines.

I'm assuming that you have mic'd the cylinders. The non turbo five cylinders were bad about wearing out the liners. Maybe you are already planning on replacing the liners.

Good luck,

Larry:

Thanks for the info. I was leaning toward the Goetze rings, but did not have any info about them. Are these made of steel, or cast iron, or ductile iron and what kind of coating do they have - chrome or molly? It makes a difference when honing because ring composition requires a matching grit to get a good seal (molly rings usually 280 perhaps 320 grit depending on how rough the stones are and their age, chrome 220 perhaps 240 depending on the stones used, cast iron 220 maybe 240 again depending on the stones used). Then I use a bead hone (some call it a soft hone) to finish the cylinder bore by removing some of the debris left from the stones and achieve a plateau-like surface that is close to a "broken-in" cylinder bore.

Yep, I measured the cylinders 6 ways (3 along each axis) with snap gauges and a micrometer (I don't like snap gauges as they are hard to get an accurate reading with, my dial bore gauge is 10mm short of being able to measure these cylinders, so I had to use what I had). Taper and out-of-round measurements are well within spec. Although the cylinders and pistons are worn a bit, they are under the service limit by a fair amount. Two of the cylinders have honing marks at the very top and the other three show significant hone marks right at and just below the area where the top compression ring changes direction. Virtually no ring ridge is present. I believe honing (removing the least amount possible) to create a good polished surface for the new rings to seat on will work fine and provide a good seal for compression and prevent oil consumption.

Any other comments or suggestions you have would be appreciated.

Tom

__________________
America: Land of the Free!

1977 300D: 300,000+ miles

American Honda: Factory Trained Technician & Honor Grad.
Formerly:
Shop Foreman;
Technical Advisor to Am. Honda;
Supervisor of Maintenance largest tree care co. in US for offices in Tex.

I'm sorry, but I don't know from what material these rings are made. They were just recommended by someone that I trust and respect. If I had a set in my hands, I could recognize if they are cast iron. Cast iron rings have a grey color to them. It seems like I remember a post here that indicated that they are a steel ring of some sort.

I will be using a set in my 240D engine when it goes back together. The engine only had about 153,000 miles after the rebuild before I had bottom end problems which necessitated disassembly. The cylinders are still beautiful with crosshatch still showing in every portion of all cylinders. If the Goetze rings prove to be cast iron, I will put the engine back together without honing the cylinders.

Not honing the cylinders for any ring is against conventional thinking, but has been scientifically proven effective by Ryder laboratories. I have used this method on several engine rebuilds over the years with tremendous success.

This probably doesn't matter because I will be surprised if these are cast iron rings, so I will end up honing the cylinders.

Since your cylinders are in spec, I expect your overhaul to produce satisfactory results.

Good luck,

Larry:

Thanks for your comments. I kind of doubt the rings will be cast iron, also, given that the 21 to 1 compression ratio would be very rough on this type of ring. I have rebuilt a couple of other diesels and they had steel or ductile iron rings. Also, I do know that the vast majority of diesels have not used cast iron rings for many years.

The gray colored coating you mention to ID cast iron rings from others is a good one, however some ductile iron rings also have a grayish colored protective finish on them. As you probably know, cast iron rings are somewhat brittle and will break easily if twisted whereas ductile iron and steel rings can be twisted without breaking. But, who wants to take a chance of breaking a ring to find out what kind of metal it is made of when you can tap the ring and listen for a ringing/bell-like sound typical of ductile iron rings. Cast iron rings will make a dull sound when tapped.

I agree that you can use new cast iron rings without honing the cylinders, provided the cylinders are in good condition. I have successfully used cast iron rings without honing several times in the past, read tech articles in the past stating that honing is not needed if the cylinders are in good condition, and recently the same info about Ryder's overhaul procedures (it may have been a post by you).

I have mic'd and used plastigage where I could on all bearings and bearing surfaces in this engine. Everything is well within spec. and only two main bearings show a bit of taper (but within spec.). All bearings and related bearing surfaces are in very good condition with virtually no wear.

I ordered the parts yesterday and should get them next week. Have you ever tried the Benz Bin for M-B parts? They sell OEM M-B parts, have great prices, and their tech support is pretty good (Tom has a lot of experience with M-B's especially engines). I've used their parts several times and I am very satisfied with them. However, the Benz Bin does not have everything (who does except M-B), so I had to order some parts through another supplier. Check them out when you get the chance.

Good Luck with your 240 overhaul!

Tom

__________________
America: Land of the Free!

1977 300D: 300,000+ miles

American Honda: Factory Trained Technician & Honor Grad.
Formerly:
Shop Foreman;
Technical Advisor to Am. Honda;
Supervisor of Maintenance largest tree care co. in US for offices in Tex.