2n with scary noise

[BigDanT]

46 2n 12v with Sherman SU tranny...While pushing/pulling snow the last couple of weeks i've noticed a knocking noise coming from the engine. The noise only rears it's ugly head under load and with the engine above half throttle. The sound seems to be coming from the rear end of the engine, say around cylinder #4 about midway or above on the block.The tractor starts, idles and revs great,no signs of loss of power,can get a small puff of smoke if I jam the throttle full but, only for a split second and clears right up. My bro in-law saw me moving snow and wants to buy the ol girl but I won't sell it to him until I know what is wrong. Not sure where to start looking here any ideas? Thanks Dan
 

[wwildhorse2k]

check for an exhaust leak at #4 cylinder first.

HTH

- Mark
 

[souNdguy]

if no exhaust leak.. read the plugs.. .. then pull one plug wire in turn to see if the knock / slap dies out

post back
 

[BigDanT]

Tractor has new manifold gasket, don't feel or hear a leak. Pulled plugs,all look the same,clean/tan. Only get the noise after the tractor has warmed up, in gear and pulling some snow. I've tried to get it to knock sitting in the shop but can't. Maybe if I jack it up put it 3Hi ??? I'll try that tomorrow too dern cold tonight...Dan
 

[souNdguy]

oil pressure ok? drop any at knock?

any possibility you are having a interference issue when hot ? IE.. did you deck the block or shave the head any?

i'd think if it was piston slap.. or rod slop.. it would do it more or less constantly unless cyl powered down..

a low op knock might appear at low rpm/pressure.. but yours it at a point pressure should be higher...

run her with 3 cyls.. leave 4 out and see if she knocks...
 

[BigDanT]

Oil pressure good...40 when first started 35 when warm. PO has passed don"t know history but I haven"t been into the engine at all. Will try 3 cylinders this weekend ...let you know. Thanks Dan
 

[notjustair]

What is your history with the machine? Is it a sharp knock or more "deep" and internal? Some have mentioned exhaust/manifold leak. I would go with that if it is a sharp tick.

This won't be a popular answer, but my first thought internally was rod bearing. I had an IH engine that did that and it was eating rod bearings. It still had high oil pressure. Those letter series engine make about double the oil pressure an N is set at, so the oil pressure might be a better indicator on the N.

If it does it all the time that means something different than if it is only after an hour of running when the oil is thinned. In cold weather rod knock is usually a little better just because the oil doesn't get as thin when it is 10 degrees outside.
 

[BigDanT]

Notjustair...I've had the tractor for awhile but just got it up and running amonth or two ago.Alot of work done to it but no engine work. Never had it under load until the snow started falling and that"s when I noticed the knock. It does seem to be a faily sharp knock...I"ll double check for an exhaust leak..other than feeling of listening is there a better test for that? Dan
 

[souNdguy]

post back after observations.

good luck!
 

[notjustair]

Rod bearings are a deep noise. Usually they don't make noise sitting and running, but when you throttle it up you will hear it and when you put a load on it you will hear it. It isn't a ticking sound but a real knock.

They usually knock pretty good on start up when there is no oil cushion. They aren't too bad when the engine is good and cold, but when that oil thins it will really knock every time you load the engine up.

It sounds like you haven't really heard it run much, so it could be rod bearings. Try and figure that out as quick as you can, cause if you run it with those bad rod bearings you will likely trash the crankshaft.

Then again, it could be an exhaust manifold leak. That would be easy and cheap!
 

[reomack]

It just might be a loose liner.