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I wouldn't be surprised if more of these motors which seem to be running OK, have one or more broken rings. lIke I do. Not long ago, did a compression check, although my motor seemed to run fine, but then, never having driven another M 37 how would I know....

The front four were about 90#, but 5 and 6 cylinders were 70# 40#'s. So, decided, as posted in another thread, to pull my engine for a total "refresh." Was over to my local machine shop, I have known him for two decades, and he had my motor all disassembled on a workbench. He showed me the broken rings on some of my pistons, below is a picture of one of them. I think the ring end gap is a bit generous.....

He told me my engine was a stock bore, but was 20 on the bearings, and 10 on the crank. I know my motor had had at least the sump off, as it was sealed with gobs of silicone. I don't know why someone would just rebuild the bottom end, and not check the bore and pistons, unless a prior owner (only several since it went to the Missouri National Guard long long ago), wanted a quick fix. He showed me some piston pin wear but the lifters are as new; he has marked them for reinstallation back into their bore. He told me to order 30 on new pistons, and 30 on the rod but only need 20 on the crank main bearings. So called VPW and ordered the rest of what I need. I already have new valves, valve seats, keepers, valve springs, cam bearings, so added timing gear and chain, in additions to a manifold and head stud set. Plus little this and that parts. While I had good oil pressure, all that metal going thru the oil pump caused me to order a new one of those too.

I asked why my motor would have broken rings; such a low compression ratio would make detonation unlikely, I would think. He told me he finds broken rings on engine tear down all the time. At least, I did't seem to do irrepairable damage to the cylinder walls. I looked at the ends of some of broken rings and some looked fresh, no carbon, but he said they just came out in pieces when the pistons came out. I have no detectable top end ridge, so who knows how long they have been in pieces. No wonder the low compression. He will line bore the cam and main bearings, and when I get him the pistons, he will balance those assembles too. His plan is to install new seats, and valves, and I can then set the clearance when they are all in. To assist me in putting it back together, he has taken lots of pictures, and will send them to me soon as a file. I make precision rifle and pistol ammunition for a variety of weapons, so am quite familiar with what 20 or 30 thousands of an inch feel line. Some wear on the crank, but no scoring.

If any forum members are willing to find "bad news" then doing a compression check might be very informative for a rebuild before things get too damaged. Of course, he has kept the main and rod caps matched to their rods and block positions.

Here is picture of such a piston....
[URL=http://s663.photobucket.com/user/h ... .jpg[/img][/url]

After a nap, I will post in the soap box the sad story of our Cat in Vietnam. He was a fighter, though. I need a nap now.

mine was running extremely well, until my new manifold leaked coolant into the motor, and i mistakenly thought the headgasket was leaking, and pulled the head, and found a broken ring and a sleeve that had dropped 3/8"
I made a sleeve puller and sucked it back up and glued it in place, and installed a new ring (with the motor in the truck, try that on a modern vehicle) and reassembled. 110# on each cylinder now

I remember your posts and pictures of your "dropped" sleeve. Nearly two years ago, when a Porsche Mechanic made a minor mistake on my GT3's engine, resulting in a repair (which they denied even partial refund for it) costing me over $7000; a single replacement piston and liner alone was right at two thousand dollars. I am going to call and order new tappet screws, so I can more precisely adjust my cold stem clearance. I am ready for the motor to come back to me; I have spent many hours making everything else ready for it. Glad your repair is holding up so far.

all the best....

NV

NAM VET, are you planning on any performance upgrades (cam, head mill, Weber 32/36, etc.)?

timing chain warning

the one i bought from vpw did not work the new chain is not the right chain for the nos timing gears
it was so tight that we had to have 3 guys to get it on
then i had to take the engine out and apart 2 more times to figure out what all of the noise was
i found that the stupid tight chain had chewed up my cam gear very bad

i ended up using my old cam gear and old chain and after all of that hassle the engine was nice and quiet

it sounds like you put a military chain on civilian timing gears (or at least a civilian cam gear)

the difference being that the military chains have a center rib, and the gears have a matching cut out for the rib to ride in. installing a ribbed chain on a non-ribbed gear would make the chain extremely tight and chew the gear up rapidly.

(i could be mistaken between which set has the rib and which set is smooth across)

I am quite famiiar with the "chewed up timing gear chain" thread of a year ago. For sure, I will make sure my new set up fits perfectly, or will reuse my old set up. My present gears have a narrow center spacer, for want of a better explanation. New and Old have to be the same for me to use the former.

And here is a picture from below of my sleeved motor.

[URL=http://s663.photobucket.com/user/h ... .jpg[/img][/url]

no the gears were military with the center rib