Hello all. Long time reader here. Thanks for all the previous advice I've received. Sorry for the long post, just trying to get all the details in. I have a late 720 diesel with a serialized pony motor that is giving me fits. It was low on power, leaked everywhere, and fogged the county when it ran. I got new rods, mains, rings, honed the cylinders, cleaned up the valves and seats. I had the crank ground to .020 under. Rods and mains sized accordingly. The engine purred like a kitten for 3 runs of about 5 minutes each then came to a fast stop. The rear main bushing welded itself to the crank on the flywheel side of the oiling hole. The crank side of the bushing looked fine. I cleaned the motor of all the shiny bits, reground the main to .030 and a new bushing again. Motor ran again 3 times for maybe 8 minutes total and seized again. Bearing to crank clearance was .003" both times. Crank endplay was shimmed to spec. New thrust washers front and rear. 5w-20 oil used. oil pressure was 45 initial start, settled in at 40psi running. Oil passages are open and clean. Flywheel side rods and journal look good still. I assume they are getting oil so that means I am getting oil through the rear main. just the outboard side of the rear main is not happy. The little drain hole in the rear main housing is open. Gasket is in place correctly. I'm at a loss. Any ideas? I feel like I'm heading for insanity trying the same things over with the same results. Such a simple little engine is getting the best of me. Thanks for any guidance.
- Thread starter Clayton78
- Start date
Yes. The hole in the bushing was aligned to the oil hole in the housing. The bushing press fit and was held with retaining compound. It didn't spin until it was friction welded to the crank. I was very cautious before the second attempt. Thought I had it. Little did I know it had me.
Thanks
Clayton...sounds like you have an expensive pony motor! What is the part number on your rear thrust plate/bearing holder? I will take a look at one I have to see if I can gain any insight on how that rear main could be starving for oil. When they ground the crank did they do a good job of cleaning it to avoid metal particles getting into small orifices?
It's getting expensive for sure. Frustrating is moving right up the list though. I washed the motor and crank with soap and water before each assembly. Rinsed heavily and dried it. The bearing holder part number is F 3 5 1 7 R. On a good note I can have the pony out and completely tore down in just under 2 hours now.
LIND BROS TRACTOR & PARTS
830 SAINT PETERS CHURCH RD SE CORYDON IN 47112
812-952-3010 833-952-3010
[email protected]
Have rebuilt motors on the shelf.
830 SAINT PETERS CHURCH RD SE CORYDON IN 47112
812-952-3010 833-952-3010
[email protected]
Have rebuilt motors on the shelf.
Where's the fun in buying a rebuild...I'm a glutten for punishment i guess. In reality that may have been a better option before I started down this road. I've already replaced all the main wear items and sunk enough into this one. everything works great except that one bearing. I'll keep them in mind if I can't get this one going after a few more attempts. I hate to let anything get the best of me.
Loosehandle
Well-known Member
- Location
- Wisconsin
If I was going to try it again I'd go
with maybe .005 clearance.
with maybe .005 clearance.
WeirdDeere
Member
I would just have to trace the oil flow path slowly and carefully to that bearing with wire, pipecleaners and air. I think each main is fed separate from the oil pump then goes thru the crank to the rods? It's been a bit, sorry. I can feel your stress, I'd be pulling my hair out
Brandon
Brandon
Just got done solvent tank washing the whole mess. The oil passages all flow fine to all locations. The crank made a trip to the lathe. I split the main bearing at the oiling groove and turned the stuck portion down to paper thin. Scraped it off with a brass rod scraper. only stuck about half way around on about 1/4" wide path right on the outer edge of the journal. I'd add a picture of it but I keep getting told I violate the anti bad word policy. I'll figure that out later. or let my techy son figure it out. either way the journal polished up well enough to try again without a machine shop visit. I also gave the bearing housing a quick hone to rule out any high spots or burrs. I didn't see any. Still puzzled but moving forward. Now i need another bushing. More clearance may be an upcoming possibility. Just don't want to overdo it. Thanks for all the input so far.
picture finally worked. right under the area of the sharpie tip is where it stuck about half the diameter. The front half of the bushing still had crosshatch from the honing showing inside once i got it off. I'm wondering if the housing may have reduced the diameter of one end of the bushing after it was pressed in. I do not know if the machine shop honed it more or just measured the front half and went with it. I did not measure the parts after I got it back. I'll check it myself this time. Should have the last time but that ship sailed already.
fixerupper
Well-known Member
Just a long shot here and a long story. Could it be an imbalance in the clutch or flywheel. I had a situation exactly like yours with an old military generator with a Willys engine. I did not make alignment marks when I removed the armature from the engine flywheel. Overhauled the engine and bolted the armature back to the engine. There are four bolts bolting the armature to the flywheel so four ways to put it back on but three ways were wrong. Well I bolted it back on wrong and there was a little vibration when it ran, more than a four cylinder engine normally vibrates. After 10 minutes the rear main locked up. Had the crank reground, put it back together, it vibrated and in five minutes started slowing down so I killed it. This time only the main bearing shell was wrecked. I bolted it back together with no rods attached to the crank or cam gear, just the crank with the armature bolted to it. With it together this way I very slowly turned the engine over. It was loose and slightly tight, loose and slightly tight. I marked the armature and flywheel and kept reassembling it one fourth of a turn different till I found the bolt hole combination that let it turn free all the way around. It was very labor intensive and nerve wracking but I finally won the battle.
Sounds like that was a similar less than fun problem. Great find on it. Subtle issue with major ramifications. The flywheel on this motor is keyed on a tapered shaft. the clutch however bolts on with a pile of bolts. I'll give it a look over for any old witness marks. I'm also going to doublecheck the crank to be sure its straight. The rod journals were welded and turned once also. machine shop said they checked for straightness but at this point everything is suspect. Thanks.
I'm just speculating her, and free advice is worth what you pay for it, but because these engines spin at a very high RPM, are you putting a thin layer of grease on the bearing surfaces to provide lube until oil can be delivered? I've seen guys do that with Cat pony engines they've rebuilt. Conceivably, at 4,000+ RPM, you could get a lot of heat buildup in the couple seconds it takes oil to start flowing. I'm sure you have thought of this, but I felt it was worth mentioning just in case.
I have been using copious amounts of engine assembly lube. Forget what brand but it has worked well in several other engines. There are only two mains so nothing has been line bored to my knowledge. The bearing area that welds to the crank is the leading edge when pressing it into the main housing. With only .003" clearance it wouldn't take much of a cone effect to make contact. I measure clearance with telescopic gauges and a micrometer. Fairly consistent readings over several spots. Not sure what the machine shop used. I haven't spoken with them yet, but I'm assuming with a new bushing showing fresh crosshatch that they didn't ream or hone it further. Guessing that's the missing bit that is causing this. Parts are on order for another try. I'm going to do a dry crank only assembly with some dykem on the journal and see what that tells me. I'll update more once the goodies arrive. Thanks.
WeirdDeere
Member
The press fit of a bearing will DEFINITELY change the inner diameter.
you would need to mic the OD of the crank and the ID of the installed bearing. If you can't mic them, you could at least put a dial indicator on the crankshaft after it installed in the block/bearing housing, and see how far it can shift up/down and even side to side. You should see that .001 to .003.
I just installed some brass bushings in a press fit. They fit perfectly before pressing, and would NOT fit at all after
Brandon
you would need to mic the OD of the crank and the ID of the installed bearing. If you can't mic them, you could at least put a dial indicator on the crankshaft after it installed in the block/bearing housing, and see how far it can shift up/down and even side to side. You should see that .001 to .003.
I just installed some brass bushings in a press fit. They fit perfectly before pressing, and would NOT fit at all after
Brandon
I'm using 5w20 at the recommendation of H&J after the first bearing failed. Said 5w20 or 5w30 small engine oil works best. Line of thinking was that I used too heavy of an oil to start with and that caused the failure. The service manual wants straight 10 or 20 weight(forget which one). Nearly impossible to find on the shelf readily available. Also says 5w20 is acceptable but with potential consumption during warmer weather or something like that. Don't have the manual in front of me for reference at the moment.
This post was edited by Clayton78 on 04/18/2022 at 04:03 pm.
This post was edited by Clayton78 on 04/18/2022 at 04:03 pm.
I did not measure it again after having the crank ground. I paid a machine shop to grind and set the clearance. The bushing was supplied already pressed into the housing. I think they missed the bushing being deformed or tapered. Whatever it was. If that was even it. That's my suspicion after all the pondering. I've had very good results at this shop and didn't feel a need to doublecheck. Lesson learned there I guess. Since the crank is still good I'm going to final bore and size my own bushing this time. If only I had my own crank grinder...
teddy52food
Well-known Member
If that is a porus bushing, did you load it 1st?
Glen D Anderson
Member
That's a good plan along with using the Dykem.
Confirm a good interference fit between the replacement bushing and the housing prior to pressing into place. Too much taper or out of round should be addressed & may even require the boring of the housing and/or the fabrication of a custom bushing with a larger O.D.
Like WD suggested, check for radial movement of the crank with a dial indicator to confirm you actually have clearance once it is assembled.
FWIW, there is a fellow(Squatch253) with a YouTube channel that has an entire series devoted to the rebuild of a CAT starting engine including several videos dedicated to the repair of the main bearing fits. Not sure how much of this is applicable to your JD engine but it gives an idea of what can be done if you are committed.
https://www.youtube.com/watch?v=Hjy8Bdd2I9c&list=PLW_TtiTWGCaqrtx5aEi85ZTwQwGRXWeMo&index=13
https://www.youtube.com/watch?v=otnCDi5d7wc&list=PLW_TtiTWGCaqrtx5aEi85ZTwQwGRXWeMo&index=14
https://www.youtube.com/watch?v=s0lZXE2bC-s&list=PLW_TtiTWGCaqrtx5aEi85ZTwQwGRXWeMo&index=15
Confirm a good interference fit between the replacement bushing and the housing prior to pressing into place. Too much taper or out of round should be addressed & may even require the boring of the housing and/or the fabrication of a custom bushing with a larger O.D.
Like WD suggested, check for radial movement of the crank with a dial indicator to confirm you actually have clearance once it is assembled.
FWIW, there is a fellow(Squatch253) with a YouTube channel that has an entire series devoted to the rebuild of a CAT starting engine including several videos dedicated to the repair of the main bearing fits. Not sure how much of this is applicable to your JD engine but it gives an idea of what can be done if you are committed.
https://www.youtube.com/watch?v=Hjy8Bdd2I9c&list=PLW_TtiTWGCaqrtx5aEi85ZTwQwGRXWeMo&index=13
https://www.youtube.com/watch?v=otnCDi5d7wc&list=PLW_TtiTWGCaqrtx5aEi85ZTwQwGRXWeMo&index=14
https://www.youtube.com/watch?v=s0lZXE2bC-s&list=PLW_TtiTWGCaqrtx5aEi85ZTwQwGRXWeMo&index=15
This post was edited by Glen D Anderson on 04/19/2022 at 11:11 am.
wore out
Well-known Member
Two things, I see there was a serial number break on the "housing" (as they call it) that the bearing presses into, what is the significance of that?
Also, has it been checked that the bearing bore is EXACTLY perpendicular to the mounting face of the casting?
Also, is it possible that the mounting face on the engine block could have somehow not been machined exactly perpendicular to the crankshaft centerline?
That is a great series of videos. I've watched a few. Slowly making my way through some more. I will be checking the bearing housing for squareness and out of round tomorrow or thursday depending on time. The block has not been measured for squareness yet. May get to that after making a new bushing. A line bore to size would work the best if either is a touch off. See what the numbers tell me. Work gets in the way of progress sometimes. Gotta keep the parts money rolling in.
The bearing housing part number break is more than likely the change in main bearing size from 1.25"(I think) to 1.5".
The bushing is not porous. I believe it is CDA932/SAE660 bronze bearing material. Not certain since I didn't make that one. That's what the next one will be made from.
Trying not to overcomplicate a relatively simple engine. It was running with .017" clearance to start with. Not well, but it was. Rods were as bad or worse. Surprised it ran as well as it did.
The bearing housing part number break is more than likely the change in main bearing size from 1.25"(I think) to 1.5".
The bushing is not porous. I believe it is CDA932/SAE660 bronze bearing material. Not certain since I didn't make that one. That's what the next one will be made from.
Trying not to overcomplicate a relatively simple engine. It was running with .017" clearance to start with. Not well, but it was. Rods were as bad or worse. Surprised it ran as well as it did.
I got the gaskets I was waiting on Saturday so I was finally able to reassemble. I bored the new bearing in the bearing housing in the lathe. There was about .001" of taper in the housing before pressing in the bearing. Either way, the bearing is round and true now. I dykemed the crank and bearings. Rear main looked really good. light even markings over most of the surface. Had a shiny scratch all around the crank journal from the front main. Little honing cleaned up whatever was causing that. I ended up with .003" all the way around on the rear main. .004" on the front main. With the bottom end assembled the crank spun easier than I remember the first two times. That was a good sign. Got it all assembled and reinstalled today. Ran for about 15 minutes so far... Still 40psi oil pressure. So far so good. Easily motored the diesel over under compression even at lower rpms. fingers crossed. Thanks for help. I'll update again if anything changes.
Glen D Anderson
Member
Good news & thanks for the update.
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