Posted: 4/18/2008 12:17:37 PM EDT
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My John Deere lawn tractor is in the shop. The mechanic first thought that I had blown a head gasket. I just listened to a phone message from him stating that it wasn't a head gasket but rather I had "impacted lifters". Okay, I know what a head gasket is, but WTF are "impacted lifters?" Anyone? |
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If it is diesel, that is really bad juju. Most gasoline engines in lawn tractors have enough clearance so camshaft timing mistakes will not cause valve to piston impact will not happen. But all OHV diesel engines, and most are, have insufficient clearance if the cam timing goes south. What happens is the lifters will collapse. And it might need a new head or at a minimum, new valves/guides/seals. |
It's gasoline. Your explanation is a bit over my head. You wouldn't have an MS paint diagram handy, would ya? 
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Crap. Sounds expensive. |
Depends on the motor make/model. Having the stealership work on it during their busiest season won't help either! Edit: Is it at a JD dealer? |
No. Local mechanic. |
Won't be as expen$ive as a JD Dealer, but depending on what it is a new engine may not cost much more. Those little bastards get spendy! Even more so when you pay someone else to work on it! |
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It would help if we knew the model/Hp/cutting swath Older side valve engines (single cylinder, under 15 Hp) can get carboned up, causing the valve to strike the carbon deposits. This will cause lifter failure. But in OHV engines, carbon usually won't build up to the point where it causes problems. If the cam drive failed in any engine, it is probably toast and not worth repair as a new engine is cheaper. |
It's a single cylinder engine. Thanks for the explanation. |
No, sounds like a carbon issue. Single cylinder engines are usually side valve. Because of the large combustion chamber area and low compression ratios, these engines are prone to carbon buildup between the valves and the cylinder head. 
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This is the patient: www.deere.com/en_US/ProductCatalog/HO/servlet/com.deere.u90785.cce.productcatalog.view.servlets.ProdCatProduct?pNbr=SKU20617&tM=HO&link=enav
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Well, "impacted lifters" sounds fishy. If the lifters are worn, the valves won't open fully and the engine will be sluggish. That engine might have a compression release which if malfunctioning, will really cut power. Kohler engines sometimes have automatic compression releases. |
The engine started blowing white smoke before I shut it down. Would that be indictative of that issue? |
I think you just won 'best in show' for MS Paint diagrams.....  |
Could be. Depends on the smell of that white smoke. More likely, if the compression release goes bad, it backfires (actually the explosion happens in the muffler) horribly under load. At idle, it could release whites smoke. These engines have governors and with comp release on, the throttle is wide open, meaning a lot of fuel is wasted. But if the smoke is very persistent, sounds like the valve guides are shot. All that is needed is a new head in that case. |
I think it sounds fishy too... a single piston engine won't run with a stuck valve. I had a 14 HP Kohler, ... it did NOT have a compression release. I'm thinkin' cracked / broken piston ring here, due to the smoke. Did it still run / miss / run real rough ?.... before you shut it down ? ETA: It seems to me - that most of the engines of this class do not have valve lifters... they run on a pushrod off the cam to lift the valves. I think you need a reliable second opinion... meanwhile start checking the cost of a new engine. |
Yes, very rough. It was all I could do to get it back to the trailer. It had backfired as well. |
I concur, these engines are not that complex, solid lifter off the cam and there are not "lifters" to "impact". Sounds to me like a broken ring problem and compression loss through the bottom end, a compression tester would easily verify that along with a bit of attention to the oil fill at the same time. Sounds like a jug, or a bore hone and top end job. I think you are being bullshitted. 
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