Tecumseh OVRM120 Valves Will Not Hold Clearance Over Time

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  #1  
Old 06-25-12, 09:08 AM
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Tecumseh OVRM120 Valves Will Not Hold Clearance Over Time

I have a Tec OVRM120-22043E that is about 11 years old where the valves are holding the clearance for shorter time each season by increasing their clearance . I have been adjusting the valves every season (about every 30 -35 hrs) to .004/.004 . This season they were out of adjustment after about 10 hrs. I always torque the locknut to the factory spec of 120 in-lb and found that this stretches the stud so that the clearance opens .002, so compensate .002 smaller to get .004 after torquing. If I just snug the locknut (to about half the torque) the stud will not stretch. Is the factory torque rating too high and stressing the bolt too much?
 

Last edited by edge10; 06-25-12 at 09:31 AM.
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Old 06-25-12, 11:10 AM
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Are they working loose, or is the cam lobe wearing down quickly to cause the need to re-adjust?
 
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Old 06-25-12, 12:15 PM
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The locknuts are not working loose. Are these engines prone to camshaft wear? Maybe it is the changes in the newer automotive oils specs reducing sliding friction additives for flat tappet engines? I am using an SAE 30 SL,SM oil, but maybe it is time for a small engine oil with a better additive package.

Any quick way to check the cam wear without a tear down? One way I can think of is a dial indicator on the push rod end of the rocker arm, if the spec valve lift is known. I can't find the valve lift or lobe height any of my Tec manuals, though.
 
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Old 06-25-12, 02:28 PM
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I don't know of any way to check it without tear down. If the clearance is changing quickly and the adjusters are not coming loose, then I'd say something is wearing. Check the push rod ends, rocker arm sockets, etc...

Oil quality isn't a concern. once a cam lobe gets scarred from either low oil level at some point in time, oil contaminates, or whatever reason, it may never "heal" or seat back and settle down. It scratches the lifter, which rotates around as the engine is running, and that scars new places on the cam, and the cam lobe and lifter fight each other, wearing each other down from that point on. This may be what's happening here if you don't find the wear elsewhere. You could put a dial indicator on the rocker arm and measure the lift, then after it needs adjusting again, adjust it and measure the lift again. If it lost the same amount of lift that you had to adjust out of the clearance, then you know it's the cam/lifters wearing.
 
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