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Oliver, Cletrac, Co-op & Cockshutt Tractors Discussion Forum
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Cannot figure out 770's engine knock?

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Gary

11-01-2003 22:01:41




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well I am working on this gas model 770. it has a faint knock seeming to come from the front but I removed the oilpan and checked rod and main bearings they look good for the age -not spun! this tractor has been well taken care of an has been under cover!although the only thing found is the oil pump drive gear seemed to not be riding in mesh deep enough. does that matter? this tractor runs very good. does not smoke idles down so well. what next? I am going to roll in new bearings any way since the pan is off! please any help!

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Canada Grant

11-03-2003 14:52:43




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 Re: Cannot figure out 770's engine knock? in reply to Gary, 11-01-2003 22:01:41  
Is front belt pulley on 770 cast centre with rivited tin pulley? Started into a 77 overhaul once and found loose hub causing noise stopped right there and that was years ago.



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gary

11-03-2003 06:30:14




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 Re: Cannot figure out 770's engine knock? in reply to Gary, 11-01-2003 22:01:41  
well thats what I am afraid of too many opinions which all are deeply needed! we previously shot trans fluid in the intake to clear any carbon build up, that did no change we grounded each cyl. no change. only thing left is timing gears or wrist pins. boy we really are not ready for the parts cost on this!!



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J. Schwiebert

11-03-2003 08:53:04




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 Re: Re: Cannot figure out 770's engine knock? in reply to gary, 11-03-2003 06:30:14  
Gary: Since you said shorting the plugs out did not change I would like to have you think about two other things. The first one I have experienced less than a handfull of times. It is more common on a 4 cylinder but I have seen it on a 6 cylinder oliver. A screw came out of the throttle shaft in the carburetor and landed on top of the piston. It hit just hard enough you knew it was there. Second do you know what a cylinder ballence test is. Find me with a U2U on the Hart-Parr section if you think I can help you.

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J. Schwiebert

11-02-2003 13:58:49




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 Re: Cannot figure out 770's engine knock? in reply to Gary, 11-01-2003 22:01:41  
A couple of questions. Did you take a screw drive and short out each cylinder to see if the noise would go away? If so when did it go away? I do not know if you kept any of the old engine oil, but if you did go to your oil supplier or NAPA for that matter and get an oil analysis kit. See what the results show. Timing gear wear would or could show traces of cast iron in the oil. Pin bushings are bronze with a steel back. On the bearings. Remember it is not a drilled crank so if you were going to use the old cotter pin trick it will not work. 770 Gas engines use the same bearings as a diesel. If the tractor has good care plastigauge them and see what for clearance you have. Also remember the rods are offset and three go in one way and three the other. Mix it up and the engine ties up. How many hours are on the engine? Timing gears can be changed with the engine in the frame. I would not worry too much about the oil pump drive. Any other comments or questions?

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Loren

11-03-2003 19:27:04




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 Re: Re: Cannot figure out 770's engine knock? in reply to J. Schwiebert, 11-02-2003 13:58:49  
Just so he knows, with the rods being offset are the bearing tang marks all lined up like on most all the engines I've seen? How will he know from under the crank? Loren



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Scott Green

11-02-2003 02:54:48




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 Re: Cannot figure out 770's engine knock? in reply to Gary, 11-01-2003 22:01:41  
Hi Gary , Neighbor had a very good machanic , with lots of Oliver experience , rebuild the engine in his "880" oliver. When all done , they started the tractor. It had a knock as you describe. He took the engine back apart. Everything looked just fine. Put it back together , still knocked. The only things not changed in the engine were the timming gears. So they changed the timming gears. Knock Gone! You might want to look at your timming gears.

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Rich

11-02-2003 02:33:12




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 Re: Cannot figure out 770's engine knock? in reply to Gary, 11-01-2003 22:01:41  
Does the noise change with engine load and speed? Louder at higher RPM, and seem to originate in the upper part of the block? They are difficult to check, but I would suspect wrist pin bushings.



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EJ

11-02-2003 14:36:44




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 Re: Re: Cannot figure out 770's engine knock? in reply to Rich, 11-02-2003 02:33:12  
Been there done that. Most likly wrist pin bushings. The old style used to be split and one side can "walk out." With the pan off you can shine up and see if there is an issue. The new style comes as a one piece job.



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Darryl Polak

11-02-2003 15:04:16




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 Re: Re: Re: Cannot figure out 770's engine knock? in reply to EJ, 11-02-2003 14:36:44  
been there before worn crank bearings



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