Main Bearings

sjw1109 · Jul 17, 2017

I have a question, about a 1 1/2 years ago I had my 9n motor rebuilt, didn't use it much last summer. It has had low oil pressure and as it warms up drops to almost nothing. Over the weekend I had the oil pump rebuilt put it back together and still the same issue. The guy I had it done at said to gauge it with plasiigage. I did this, now I have no clue what im looking at, is there anybody that could tell me if it is a bearing issue if I post what I got.

bearing is 010
slightly larger than .004in on one side and the other side reads.
.102mm.

Thanks

TheOldHokie · Jul 17, 2017

(quoted from post at 05:57:47 07/17/17) I have a question, about a 1 1/2 years ago I had my 9n motor rebuilt, didn't use it much last summer. It has had low oil pressure and as it warms up drops to almost nothing. Over the weekend I had the oil pump rebuilt put it back together and still the same issue. The guy I had it done at said to gauge it with plasiigage. I did this, now I have no clue what im looking at, is there anybody that could tell me if it is a bearing issue if I post what I got.

bearing is 010
slightly larger than .004in on one side and the other side reads.
.102mm.

Thanks

Plastigage measures the oil clearance which is teh difference between the OD of the crankshaft journal and the ID of teh bearings. If I understand your numbers the plastigage indicates a .004" oil clearance which is the same as .102mm.

That is considerably wider than what I would expect from a freshly rebuilt engine. A new engine should be close to .001-.0025. Plastigage is not terribly accurate but at .004 you are close to the wear limit which is .005. After 60+ years these engines are already pretty worn throughout and that sort of main bearing oil clearance will definitely pull oil pressure down....

TOH

ASEguy · Jul 17, 2017

Is the engine out and on a stand or still in the tractor? If done correctly the clearance is too much, but not necessarily accounting for dropping to almost nothing. When I Plastigage, I have the block out, gently set the crank on dry bearings, put Plastigage across the entire journal of both mains and rods (rods one at a time)and torgue to spec. without spinning the crankshaft. Plastigage is only a double check. All main and rod journals must be checked for actual diameter, out-of-round and taper to ensure hydrodynamic lubrication will occur. If you only checked one journal, it's not conclusive. Unless something was done to the tractor after the overhaul, I would have an issue with the individual that performed the overhaul. When done properly oil pressure should be good for a long time. Post pictures of the bearings if you can. Hope this helps.

Ultradog MN · Jul 17, 2017

Speaking of plastigage,
I wrote this a few years ago...
Plastic gauge

sjw1109 · Jul 17, 2017

Yes I do have a problem with the person that put it together, he had me get 010 for the main and 030 for the rods. I took the motor apart and everything to the machine shop. The motor is still in, and cam and crank all were good. Do you think that I need to get a size larger for the main bearings. I do have to apologize just because I do not know the internals of a motor, but I am learning as I go. Since the rebuild it has only been used a couple time, no work was done with it.

TheOldHokie · Jul 17, 2017

(quoted from post at 07:47:20 07/17/17) Yes I do have a problem with the person that put it together, he had me get 010 for the main and 030 for the rods. I took the motor apart and everything to the machine shop. The motor is still in, and cam and crank all were good. Do you think that I need to get a size larger for the main bearings. I do have to apologize just because I do not know the internals of a motor, but I am learning as I go. Since the rebuild it has only been used a couple time, no work was done with it.

Yes - I think you need the next under size main bearings but they will be .020 under and for that you need to have the crankshaft reground to match. Am I correct in assuming the machine shop that did the overhaul for you simply replaced the old bearings with new ones without regrinding the crankshaft? If the crank was reground you also need a new machine shop. In fact you need a new machine shop in either case.

TOH

sjw1109 · Jul 17, 2017

I probably should of put it better, but I am at work so trying to type quick so no one sees. The machine shop did the cleaning of the block cam and crank. It was someone I had met that put it together for me, he advised me of what I needed.

sjw1109 · Jul 17, 2017

(quoted from post at 05:12:39 07/17/17) I probably should of put it better, but I am at work so trying to type quick so no one sees. The machine shop did the cleaning of the block cam and crank. It was someone I had met that put it together for me, he advised me of what I needed.

Now if I was to put 020 in could I get through the summer with that, then tear it down and have a machine shop rebuild it for me over the winter.

R Geiger · Jul 17, 2017

(quoted from post at 07:03:47 07/17/17)

(quoted from post at 05:12:39 07/17/17) I probably should of put it better, but I am at work so trying to type quick so no one sees. The machine shop did the cleaning of the block cam and crank. It was someone I had met that put it together for me, he advised me of what I needed.

Click to expand...

Now if I was to put 020 in could I get through the summer with that, then tear it down and have a machine shop rebuild it for me over the winter.

NO, 020 would bind it up, either live wive with the oil pressure and gamble that you will not destroy the engine or have the crank turned for the 020 bearings.

Den N Ms · Jul 17, 2017

Sjw1109,The other thing you could do other than have the crank reground at this time would be to use like some .002 brass shim stock under the bearing insert to tighten up the clearance on the main caps.

sjw1109 · Jul 17, 2017

(quoted from post at 08:21:43 07/17/17) Sjw1109,The other thing you could do other than have the crank reground at this time would be to use like some .002 brass shim stock under the bearing insert to tighten up the clearance on the main caps.

Its worth a shot, where I can I get them.

HFJ · Jul 17, 2017

i like the sound of this as a temporary fix. the going rate for a 6" x 100' roll seems to be ~ $30 bucks, plenty listed on both ebay and amazon.

den, would steel shim stock be ok too?

Den N Ms · Jul 17, 2017

HFJ,I have always used Brass or even Aluminum on bearings,I believe it allows the fit tighter together for a better fit just my opinion.

TheOldHokie · Jul 17, 2017

(quoted from post at 11:21:43 07/17/17) Sjw1109,The other thing you could do other than have the crank reground at this time would be to use like some .002 brass shim stock under the bearing insert to tighten up the clearance on the main caps.

If doing so use it (.002 shim) on one side only (lower half) and you will need to remove about .002 from both ends of the lower insert or you will only make matters worse. Shimming a modern insert bearing is witchcraft at best.

TOH

ASEguy · Jul 18, 2017

Amen to that. I have never regretted doing the job right.

sjw1109 · Jul 18, 2017

(quoted from post at 04:40:03 07/18/17) Amen to that. I have never regretted doing the job right.

Still not sure what im going to do yet, now if I decide to take in to get ground, can I remove if wth the motor still in, or would I have to take it off the tractor?

TheOldHokie · Jul 18, 2017

(quoted from post at 08:16:53 07/18/17)

(quoted from post at 04:40:03 07/18/17) Amen to that. I have never regretted doing the job right.

Click to expand...

Still not sure what im going to do yet, now if I decide to take in to get ground, can I remove if wth the motor still in, or would I have to take it off the tractor?

You will have to remove the flywheel from the rear of the crankshaft which at a minimum requires splitting the tractor. The flathead is not difficult to work on and it's not a huge job to pull the engine and do the needed work on the bench.

That said you may have more going on than just poor bearing fitment. You really should check the main and connecting rod bearing housings for size and roundness while you have them out. New bearings in a hogged out housing aren't going to give you a proper fit even with a newly ground crankshaft....

TOH

jimtrs · Jul 19, 2017

That said you may have more going on than just poor bearing fitment

Agreed

If done correctly the clearance is too much, but not necessarily accounting for dropping to almost nothing

Agreed

The machine shop did the cleaning of the block cam and crank. It was someone I had met that put it together for me, he advised me of what I needed

The machine shop needs to be the one telling you about your crankshaft.

Shimming a modern insert bearing is witchcraft at best.

Amen to that. I have never regretted doing the job right.

Don't even think about shimming under an insert. You are likely to spin a bearing.

I had my 9n motor rebuilt, didn't use it much last summer. It has had low oil pressure and as it warms up drops to almost nothing

There are other things that can cause low oil pressure. A rebuilt good pump should yield more pressure than you will use. Just swapping out gears (if that is all that was done) is not a rebuild.

The guy I had it done at said to gauge it with plasiigage. I did this, now I have no clue what im looking at

All the more reason to have a reputable machine shop look at it.

If it were mine, I would remove the engine, strip it down and send it off to a reputable machine shop for evaluation. Unfortunately you already paid once to redo your engine, but it's not right. The correct thing to do is to do it again, but have it done correctly. It's not rocket science. Just need a real machine shop and a real mechanic, not just a wrench turner.

Main Bearings

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