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Spun bearing on 990

Posted: Tue Apr 16, 2019 10:21 pm
by tinmantom

I have a 990 which started to drink oil, developed a knock and was giving out white smoke. I dropped the oil sump and found some swarf and a nut (!) which was a bit of a shock.

The nut was from cylinder 1's big end bearing - I took the other one off and found the bearing had spun and either disappeared or welded itself to the conrod. I also noticed oil seemed to be seeping a bit from the head gasket so thought it was time to dive in, clean everything up and get the head off.

No obvious cracks to the head and checking it with a steel rule and feeler gauges I can't find a warp. I did however find a couple of the water-ways were clogged up with rusty deposits and one had a fairly sizable bit of liquid-gasket which I tweezered out - the water pump has a fairly messy liquid gasket which I haven't removed yet but I assume I will for the rebuild.

I guess that the head is not originally from the same engine as the block - there is a waterway in the head that I don't think has a corresponding way in the block (although it had produced a bit of a rusty bump which I've gently scraped back down to level) - when the new gasket arrives I hope it will just have the holes for the block... The second discrepancy is the air manifold ports have three bolts on the head but only two on the manifold so the extra ones have been cut off. A fairly rough job was done though so some of them are up to 2mm proud - obviously taken up by the gasket previously but wondering whether folk think I should do a better job of making them level. Block serial number is Mc25389, head is F921438.

I guess I'd be keen to hear peoples thoughts on how precious I should be about trying to get the crankshaft and big end journals smooth before I reassemble (with new bearing shells) and see if things are in better shape. I've got the journals fairly smooth but there are still some grooves. And I'm yet to get to work on the crank but have been watching various videos involving shoelaces and honing paste!

Apologise if any of the terms aren't right here - it's been a steep learning curve this week! I did rebuild my car engine when the timing belt snapped but I had a haynes manual for that - this time all I've got is the head torquing pattern in the maintenance book so I feel like I'm winging it a bit - any do's and don'ts would be greatly appreciated!



Re: Spun bearing on 990

Posted: Tue Apr 16, 2019 10:51 pm
by db2d
Can you supply the engine number please so that the engine type can be identified

Re: Spun bearing on 990

Posted: Tue Apr 16, 2019 11:18 pm
by tinmantom
Excuse my ignorance where do I find that? - the block has E W 2 , 2 A O and Mc25389 cast into it. Then the printed label has 10279 written on it.

Re: Spun bearing on 990

Posted: Wed Apr 17, 2019 6:47 am
by db2d
Stamped in the cylinder block on the lower front corner below the dynamo.
The numbers you have supplied are casting numbers.

Re: Spun bearing on 990

Posted: Wed Apr 17, 2019 6:58 am
by cobbadog
If this is your tractor and you are going to put it back towork don't mess around have your crankshaft machined properly. You will thank yourself for that later on in years of reliable use. Once machined you will then know what size bearings you need to buy.
Simply cleaning up the journals is not the best way to get a good result even it is jsut to rum around the parade ground at Rallies. I have never regretted doing my engine up properly and after almost 4 years of running the tractor at Shows and on treks it is comforting to know that it is a reliable tractor and not waiting for the same bearing to spin again due to an improper repair.

Re: Spun bearing on 990

Posted: Wed Apr 17, 2019 9:12 am
by philedge
Where you go from here depends on how deep your pockets are, how much time you have and how important the tractor is to you.
For what you could spend on an engine rebuild you can probably buy a running tractor.

If the journal is scored but smooth you may get away with a polish and new shells. If your on a budget or can afford for the tractor to be out of service in the future clean up the journals as best you can an put some new shells in. See how the oil pressure is once the tractor is running again. Id give the con rod a good inspection if its been run with the cap loose and if youve got the head off maybe put a replacement rod in. If you want to spend money and/or the tractor is important to you then spend the money on a rebuild.

Bear in mind that if one journal is scored its likely through neglect and other parts of the engine may be worn too.

Re: Spun bearing on 990

Posted: Wed Apr 17, 2019 12:35 pm
by tinmantom
From behind the lift pump I see K956168F - if this isn't it do I need to take the dynamo off to see it?

Thanks for everyone's input so far. We use it for an intense few days once a year to do a hay cut on 30 acres - the rest of the year it is infrequently used to move trailers of logs down to the house, occasionally grade the lane and drive a log splitter off the pto. I wonder whether the splitter might be the cause of this - it's a new addition and I've been reading that running such things isn't a nice regime for the engines.

I assume that getting the crank out for machining means bringing the whole block out? What would be a reasonable price for machining the crank in the UK?

Pockets aren't super deep, time is indeed very short (not least because without a barn everything feels very vulnerable opened up as it is) and although the tractor is important it's mainly important as a working machine which - as Philedge points out - we could well get a replacement either as a donor engine or a whole new tractor.

By inspecting the con rod do you mean for cracks?

Re: Spun bearing on 990

Posted: Wed Apr 17, 2019 12:58 pm
by ollek
The number K956168F is a casting number, not the engine serial number. As said, the engine number is stamped on a small flat surface below the alternator, not behind the lift pump, and the number can be painted over. The number should start with AD4 for the engine type and then go on with numbers only.

Re: Spun bearing on 990

Posted: Wed Apr 17, 2019 10:19 pm
by bedwards1966
Obviously your crank is not very healthy. If you can see rings round any of the journals it should be reground to make things right.

However, for an engine that's only doing fairly easy work on a small scale you can sometimes get away with spending some time with strips of very fine emery to polish it up and make it all smooth, provided there's no deep damage. If you can catch a fingernail on any of the marks, get it ground. If you want to know that it's all done properly, get it ground.

When you have the head off you will probably find that it would benefit from some attention to the valves, generally head work isn't expensive.

Re: Spun bearing on 990

Posted: Wed Apr 17, 2019 10:26 pm
by philedge
For the con rod, if the engine has been running for even a short time with only one bolt in place and one or both shells missing check for cracks, distortion or bruising where the shells sit.

To get the crankshaft out for repair Im pretty sure youll need to split the tractor to get the flywheel off so you can remove the crank.

If you want an engine service manual, search the forum for haynes manual and youll find a thread with a link to a load of manuals. Theres a whole load of service info in one of the folders.

If your working outside see if you can borrow a gazebo or get a clean tarpaulin to throw over the tractor if the weather turns sour

Re: Spun bearing on 990

Posted: Sat Apr 20, 2019 11:23 pm
by Gard
I do not have much experience rebuilding engines but would assume you will need a new connecting rod. I think you should be able to measure the crankshaft diameter to see if it is within spec (from service manual). Might be a good idea to pull the pistons out and try to get an idea of overall cost before proceeding. I have no idea if your head is original or not.

Re: Spun bearing on 990

Posted: Tue Jun 11, 2019 11:23 pm
by tinmantom
Hi all,

So I got a quote from our local chap to split everything, re-grind and reassemble and it is going to be £900. I am keeping my eyes out for a donor engine as fitting that would apparently be quite a bit less time than extracting the crank, but I haven't found anything yet. May still end up forking out for the rebuild but it's a lot of money for us and we are considering whether we really need a tractor at all - maybe we should just be hiring in for the few occasions a year a tractor is needed...

With this in mind I was keen to see how far I could get with very low spending...
So I've cleaned up the journal pretty well with increasing grit wet and dry paper - with the oil-way plugged to stop grit getting in - and I've got it so I can't feel anything when I pass my nail over it. I've fitted new original size shells and can't feel any play at all.

But, since we have never really worked the engine very hard at all... And to give it the best shot at not spinning again and throwing shrapnel all over the place... I've decided to take the injector out of that cylinder and route the fuel into a long pipe that currently goes into a jerry can in the cab.

It take a few extra cranks to start but once it's going it feels very smooth... Sounds a bit like an old narrow boat with the air rushing out the injector hole!

This post implies it's going to do harm:


But my engineering dad says:
"I am not sure I agree with the statement that running on 3 puts additional load on the bearings. Running on 3 will undoubtable introduce additional low frequency torsional forcing (at ½ engine rotational speed/frequency) which if it hits a driveline torsional resonance, could well cause some damage; could even crack the crank. But you usually hear if it sits on a severe torsional resonance (lots of clatter)."

I've run it for about an hour now but never for more than 10 minutes so it's never got warm yet...
Going to drop the sump again and have a look at the condition of the new shells over the weekend, do an oil filter change and then have a go at letting it get warm.
Question is - should I maybe run on some thicker oil?

Sorry if this course of action upsets people - I know that to many this may seem like a fool-hardy false economy. Fact remains that the economics of owning a tractor at all are questionable going forward so this is a bit of a last life for the machine.

Thanks again for your thoughts.

Re: Spun bearing on 990

Posted: Wed Jun 12, 2019 7:04 am
by cobbadog
At the end of the day your repair will only be as good as your cost input. A cheap repair means it is not done right and may not last very long where a proper repair will give years of service.
Feeling if there is any movement is not how you can test for tolerances, they must be measured using calipers or a micrometer to know what size the journals are and is they are out of round. I certainly wouldn't recommend running your engine on 3 cylinders especially with the history the engine has already, it will be very unbalanced and will hammer away at your main bearings.

Re: Spun bearing on 990

Posted: Wed Jun 12, 2019 8:01 am
by rid54
Since we're in the realm of opinion here, I venture mine:

Taking out one of the cylinders will put some extra stress on the crankshaft, as it increases variations the rotational forces. The torsional stress on the crankshaft will increase and, in an unlucky event, torsional resonance might appear at some engine speed. This may lead to shearing of the shaft; if cracks appears somewhere, they will grow rapidly. The engine will not be unbalanced per se, as all the mechanical parts are still in place, but the "empty power stroke" may cause other problems.

Depending on the situation, I might be tempted to run the engine as is (with the new bearings etc), but if a catastrophic engine failure occurs, other parts (e.g. transmission) that are now in good shape may suffer damage and that might be a severe setback.

Re: Spun bearing on 990

Posted: Wed Jun 12, 2019 9:22 am
by philedge
Suggest you put an accurate pressure guage on the oil supply and if the pressure is good reinstate the fourth cylinder. If the pressure is good your big end must be in fair shape.

Id be tempted to wire a siren in parallel with the oil warning light so you wont mis any drop in pressure and you can shut the engine down before total destruction!!