rod bearings

[Eoghan]

I've been pushing snow around with the cub for a few weeks since giving it a good tune up/new wiring/plugs etc, and I've had no problems other than when it sits for a few days and i go to start it up there's a quiet knocking for about 3 seconds after the engine starts up, then it goes away. I also had an issue last year (I discussed it here) with a slight knocking when mowing the lawn at high rpm for extended periods of time. I've realized since that the governor wasn't working properly and I should not have had to run it at full throttle like that. Anyways, my thinking is that this indicates a bad rod/main bearing. I don't have a ton of $$ or time to do a full-on rebuild right now, so I'm wondering if it's possible/advisable to just drop the pan and swap out the bearings. I know it's not the "right" way to do it, but I need the tractor to pull a plow this spring. From reading around this forum I've seen this issue debated, but I wonder what would the drawbacks be exactly? I understand I might mess up the rear main seal, but i'm prepared to split and replace that if i have to. Pulling the whole engine off seems a little more daunting.. Also I understand that next year when I CAN afford the overhaul I might have to turn the crank which would mean buying new oversized bearings, correct? Also, am i correct in thinking the only special tool i'll need to do the bearings (besides patience to get those pan bolts off) is a torque wrench? Lastly, if I go ahead with it, should I replace all of them, or should I use something like plastigauge to determine which need replacing, and just do those? What I'm really hoping for is a band-aid to prevent further damage until i can really tear into it hopefully next fall/winter. I use the tractor in the spring and fall to pull a plow/disc over about an acre, and I'll be using it for cultivating this year as well. I'm going to get another machine to mow the lawn however.. seems kinda hard on the cub, and the c3 doesn't make it look very nice. not to mention the time it takes to put it on!

[Mike in Louisiana]

Does it do this knocking every time you start it ?????

Only lasts for 3 seconds..

could you be loosing prime on oil pump ???

[Eoghan]

Does it do this knocking every time you start it ?????

Only lasts for 3 seconds..

could you be loosing prime on oil pump ???

It only does it when it's sit for a few days without starting, and only the first start of the day. I'm imagining the oil film is seeping out of the bearings as it sits and it takes a few seconds for the oil to travel to the offending bearing after starting. If the pump lost prime i wouldn't get pressure at all, would I? it picks up fairly quickly and the knock goes away completely. also the high idle knock was traced with a stethoscope to the bottom end on the front side. probably #1 or front main.

[Hengy]

You can replace the bearings with the engine in the tractor, but it sure would be easier with it out. With the engine in the tractor, you can remove the bearings, and check the surface off the journals. Should be smooth as glass and should be round and not egg shaped. Measure the rod bearing journals with a caliper at several places around the journal and make sure that they are really close in dimension. (I don't have the acceptable out of round specification). Your bearings should say what dimension they are (Std or under). If you order new bearings, use some plastigauge to measure the clearance between the bearings and the journal.

One thing that I was advised to check before I disassembled the rods and mains was to check each rod for side-to-side motion. They should all be tight.

Is your oil pressure low when running? That would give an indication of the bearings wearing a bit.

Of course, the best thing to do would be what Eugene usually suggests... Remove the engine, completely disassemble and measure everything.

[ricky racer]

or should I use something like plastigauge to determine which need replacing, and just do those?

That is where I would start. See what you've got and go from there. It will cost you next to nothing to check the bearings out and it will let you see the bearings and journals conditions. If the bearings are good, you'll need to look elsewhere for the problem.

[Eugene]

'I don't have a ton of $$ or time to do a full-on rebuild right now. Also I understand that next year when I CAN afford the overhaul I might have to turn the crank which would mean buying new oversized bearings, correct?

You can replace the rod and main bearings without doing a major engine overhaul. Consider, that you will be probably wind up purchasing two sets of bearings and pan gaskets if the crankshaft needs to be machined.

Suggest doing an in tractor over haul if the crankshaft checks out as good. Rings, rod and main bearings, lap the valves.

I'm looking at the situation from my perspective. I have the tools for most engine work. Providing the engine does not need extensive machine work, can usually overhaul a 4 cylinder engine for under $300- in parts.

[Smokeycub]

Suggest doing an in tractor over haul if the crankshaft checks out as good. Rings, rod and main bearings, lap the valves.I'm looking at the situation from my perspective. I have the tools for most engine work. Providing the engine does not need extensive machine work, can usually overhaul a 4 cylinder engine for under $300- in parts.

if I go ahead with it, should I replace all of them, or should I use something like plastigauge to determine which need replacing, and just do those?

Chances are the one you hear knocking is well over clearance specs and the other rod bearings are nor far behind. ...and equally so with the main bearings, that's been my experiance. Like Ricky says a visual inspection and the plastigauge will tell the story. Even if you don't do the rings now, for what they cost I would replace them all, main and rod bearings. How is the oil pressure hot at idle?

[Eoghan]

Thanks guys! I feel better about this now. I want to do the rings/valves too, but I'm afraid if I take the head off i'll get myself in too deep.. also I'm not sure how/don't have the tools to measure the cylinders/pistons/rings. what special tools will I need to do the rings?

How is the oil pressure hot at idle?

after about 20 mins of hard work the oil pressure at idle is in the red and it knocks slightly at maximum throttle. I think that's pretty much textbook

[Bob McCarty]

Here's a link to a post by Art that may help: viewtopic.php?f=141&t=35239

Bob

[Eoghan]

Thanks Bob,

That post was quite informative.

[artc]

from what I've read on this thread, it's likely that a rod bearing is trashed, and probably #1 cylinder because it is the farthest from the oil pump. classic symptoms - knock at cold start - then heavy oil gets into bearing and quiets it down - oil heats - rod noise at high RPM's and low oil pressure.

it is unlikely that the crankshaft journals are good. Which means that the engine has to be removed from the tractor.