Pumpkin Problems

[SasquatchSanta]

It's totally illogical but I've picked up an engine noise in the M37 (Pumpkin) engine.

What's illogical about it is the engine was completely rebuilt, clear down to boiling the block, boreing .030 over --- the works several years ago. Granted, it was several years ago but I would guess it doesn't have over 200 hours on it and it's certainly never been abused or reved over 2,500 RPM.

The noise started out about a month ago as a slight peck/clunk when I started it up in these cold Minnesota mornings. The only time you could hear is was when it was under a slight load. Running along at 4 or 5 MPH in first gear it would make noise when the engine was pulling. Once you let your foot off and let it coast it would quiet down. It would also quiet down when it warmed up.
It's now getting louder.

It doesn't sound or act like a rod. It's got good oil pressure that holds steady through all RPM ranges regardless is your climbing on it or getting out of it.

I did a compression check. All cylinders are between 135 and 150 pounds compression. When you pull number-one plug wire off it quits making noise.

It could be a front main but I doubt it. I think it's a cracked piston skirt or a pin. The question is, what the heck would cause that to happen to a fresh non-abused engine. I could see a piston skirt cracking on an engine that had some cylinder wear (piston slap) but this engine was bored 200 hours ago and new pistons (and pins) installed.

I'll know more tomorrow. Soldier number one and I are pulling the head and pan tomorrow morning along with number-one piston.

More to follow.

PS: Do you think because these engines have a long stroke that cold morning starts could crack a piston? It goes without saying that I doNOT rev up the engine until it's good and warmed up. I'm running 10W30 motor oil.

 

[Westech]

well mains don't "clunk" they squeal. Remember when the new Gm engines came out in the 1999 trucks? and they all "knocked" till they got warmed up. Well it was a problem with the piston skirt and would make noise till it got warm and expanded. Could just be a size problem due to over boring and honing. If you see no bits in the oil and the spark plug is not smashed in by piston contact not a lot you can do besides tare it down and take a look. if it were me... I would use really good oil maybe in the 15w40 type and run her. but if it is getting louder.. piston side slap really does not get worse just a noise when cold... I might pull the oil pan and take a look top side and see if you can find any chips or cracks. I think this is going to be a connect the dots type of thing.

 

[SasquatchSanta]

I would run it if it wasn't for fear that it might be a pin that could score a cylinder wall.

One of the nice things about a flathead is that it doesn't take long to pull the top and bottom off.

 

[doghead]

Sounds like piston skirt slap. Look for undersized piston skirt or out of round cylinder bore. If it's getting louder, then your doing what you should do, find it.

 

[maxim]

Sticky tappett?? Tappett that came out of adjustment?

 

[M543A2]

Main bearing problems are heard as a dull thump, usually on start-up and under load, especially with warm oil. Rod bearing noise is a sharper double knock, with the same start-up and warm oil symptoms of the main problem. A wrist pin will not usually change tone with oil pressure unless the motor has rifle drilled rods. It cannot be a tappet because it would not change when the spark wire is removed. I think you are on the right track with taking it out for inspection. I also suspect a piston problem of some kind. I have started M-37's in very cold weather consistently with no problems. The oil you are using should be good for the application. The stroke has nothing to do with it; many of our farm equipment motors have longer strokes and they are no problem. I learned the hard way several times new parts can go bad! Good luck, and let us know what you find.
Regards Marti

 

[SasquatchSanta]

Update

First off --- thanks for all the input --- much appreciated.

We pulled the head and pan today. The pistons look like they came out of a chain saw that someone either ran too lean or didn't put enough oil in the gas. Nr-1 piston was the worst with scoreing on both sides. The others weren't as bad and a couple were barely scored. The block is OK. Some light honeing will clean it up --- no problem. All the bearings (rods, mains) look new.

The problem --- gas in the oil! I ran the starter for 30 seconds twice with the pistons out to check for gas leaking into the block from the fuel pump. No leakage.

The only thing I can figure out was up until a couple of weeks ago I was running a carburator that was running rich. Evidently it was doseing so much gas to the engine that it was by-passing the rings and getting into the oil pan. With the new carburator the engine runs a lot better. My fuel mileage still sucks but the truck stopped making gray smoke and it smells and runs better. I'm running civilian carbs and outside of checking the plugs I don't know how to tell when it's getting too much fuel. I sure as hell don't want this to happen again.

Thankfully, the block (cylingers), rods, mains and crank are OK. We are going to home the cylinders and install all new pistons and rings. I could probably get by with only installing one piston but I might decide to sell this truck someday and I would feel bad is someone had trouble (an engine failure) because I didn't fix it right. Sometimes having a conscious sucks.

The engine looks new inside --- probably becaus it is --- It only has about 200 hours on it.

Something else I want to mention. Before installing this engine last fall we installed a civilian head that had been milled .040. It seems to run a lot better with the milled civi head (civi heads are rumored to be higher compression) but since installin the new head the engine runs at 195 degrees with a 180 degree thermostat --- in Minnesota winter. It never ran hot before but even when it's idling it runs at 195. That concerns me. It will cost me some performance but I'm thinking about putting the old stock M37 head back on. Could it be that since the rings were seated for a lower compression, when the high compression head was installed it not only causes it to run hot --- it also caused blow-by that deposited gas in the crank case???

I also think for a while we had the engine timed too fast. At the time we didn't have a timeing light and the guy helping me said to time it as fast as you could without it kicking back when you start it and then take your foot out of it so it doesn't ping on the hills. It seems like fast timeing could also cause blow-by. It's new times properly.

Outside of occasionally smelling the dip stick I don't see any other way to check for gas in oil. I don't want this to happen again.

Also, I'm damned sure gong to keep my eye on the Deuce (Rosie) for fuel in the oil. I don't want the same piston problems in the multi.

I'd like to do some carb re-jetting. Any Ball and Ball carb gurus out there?

 

[doghead]

Actually, running lean and hot can make the pistons look like you described. If the the oil was compromised(with gas), I would expect bearing damage to be evident also. set the timing right, for sure.

 

[nk14zp]

How are your plug wires? I cracked a piston with a bad plug wire then blow by blew oil off crank then a rod came out that was on a IH345 in a bus.

 

[SasquatchSanta]

The Plot Thickens

It pays to check and double check details when you're doing forensics. Today I discovered that all the rods except one were installed with the oil cooling/lubrication port (squirt hole) in the crank end of the rod pointed in the wrong direction?

The holes squirt oil on the piston and cylinder wall and are suppose to be pointed toward the valve side of the engine. Number two piston/rod was the only one pointed in the right direction.

Gas in the oil was what did this engine in but the oil holes pointed toward the distributor side of the block were no doubt a contributing factor.

This engine was boiled rebuilt and assembled by a big shop --- Wigamon Brothers in Minneapolis. They must have had a new guy on the project --- or an old guy that didn't care.

 

[doghead]

Well, atleast you know why, now.

 

[amanco]

Boy, that is a MAJOR no no. Rods facing the wrong way. Testament to the engine's survivability though. My pistons had side clearance of 25 thousanths. Piston slap let about 5 of the wrist pin retainer clips loose. Cylinder walls were pretty well gouged and still started right up. Got that all taken care of though. If time is not an issue, building one of these flatties is a lot of fun. Lot of history in that there engine.

 

[SasquatchSanta]

On The Road Again

Soldier Number-One and I finished putting the Pumpkin back together Friday afternoon. It runs better than it ever has --- or at least better than I can ever remember.

I'm damned sure going to watch my oil from now on. I cringe to think what it would have cost to turn this project around had it have been a new "modern" vehicle. I'm glad only own and drive old iron.

Thanks for all the insight

 

[rosco]

That was a very good engine, and was one of the most popular in the world for many years. Assembly..... Like your rods facing one way - the valve springs have a top & bottom too! If they are assembled upside down, they will fail (break), after some running. All those old carburated engines can have oil dilution. You just have to keep after the carb setting, but that is not ironclad either. The float level is real important, in that regard. Fuel/gas dilution was a major cause of wear.

The heads were prone to warping & should always be checked. The last 230 cu engine I built, the block was out too - .005 & the head was warped .015. The manifolds were also prone to warping. The "Old Guy" mechanics, new all that stuff because they were around it more. Now, few of us get to build engines. The old iron wasn't real complicated, but had it quirks.

What head did you end up using? i found that milling the head did little to performance.

Lee in Alaska

 

[SasquatchSanta]

Lee in Alaska wrote:

What head did you end up using? i found that milling the head did little to performance.

That's a little bit of a long story. Once upon a time I was told that the heads on the civilian engines were better --- had more compression. It was with that in mind that I took a head off an engine that was in a 1950 pickup.

It sat in my garage for years --- long enough for me to forget that it had the bypass bubble on the front. Without double checking, I had it milled .040 and installed it when we built the truck in October. Naturally, it leaked. I knew better but wasn't thinking. We pulled it and put a plug in the head were the bypass hole goes. In doing so it now uses the water pump bypass and works fine.

I was a little skeptical about using it when I realized it was a diferent (bubble-front) head but after looking closely and comparing the two heads the only difference seems to be the water bypass hold --- which is now plugged.

Because it was a civilian head I don't know what compression the .040 milling produced. I feel it made a marked difference in performance.