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Tractor Talk Discussion Forum

Engine analysis needed here ....

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Way Up Here

05-26-2006 06:25:47




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OK, here's my situation. I have a 4-cylinder Continental flathead 124 cid engine in a MH model 20 which blows a lot of blue smoke when it gets warm, especially when you rev the engine up quickly. The compression reads between 100 & 110 pounds so that seems OK. Tearing the engine down showed me exhaust valves in very good shape (carboned up underneath the valve head) and the intake valves have a ridge pounded into their circumference near the bottom where they contact the bottom edge of the seat. They were also carboned up underneath somewhat. The valve guides (intake and exhaust) are quite slopppy. I have no idea what condition the rings or cylinder bores are in but the bores look clean and unscored haven't torn that apart yet (if I do that at all) but there is almost no wear ridge on the top of the cylinder bores. Tops of the pistons are relatively clean with just a bit of carbon and oily residue. My question is .... what is causing the engine to blow the oily smoke?

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chris sweetland

05-27-2006 13:42:00




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 Re: Engine analysis needed here .... in reply to Way Up Here, 05-26-2006 06:25:47  
i tend to lean twords valve guides but if thats got an oil bath air filter make sure your oil in the filter isnt too thin



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buickanddeere

05-27-2006 08:08:29




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 Re: Engine analysis needed here .... in reply to Way Up Here, 05-26-2006 06:25:47  
When at idle the intake manifold is under high vacuum,low flow volume and slow flow velocity. All the oil that has seeped through the valve guides.And all the droplets of gasoline stuck to the side of the manifold and puddled wet on the bottom of the manifold. Is just sitting there waiting. Now when you give the throttle a snort and rev her up.There is a few seconds where that accumulated oil/gasoline will be drawn into the combustion chambers and cause a smoke show. It's the nature of the beast having a carburated/wet intake manifold. That's why auto manuafctures went to fuel injection. Unless the manifold is dry and the fuel squirted into the cylinders just behind the intake valves. There will be a momentary over rich condiiton every time the carburator throttle is opened/rpms increased from low power/low rpm conditions. High vacuum caused by a clean appearing but internally plugged oilbath aircleaner/pipework will contribute to smoke as well. So replace the valve guides and valves. Set the idle screws as lean as the engine will run without missing. Keep the coolant at 195 which helps warm the manifold. And use manifold heat if avalable on gassers that just putt around and don't plough at full power all day.

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Jerry/MT

05-26-2006 21:01:29




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 Re: Engine analysis needed here .... in reply to Way Up Here, 05-26-2006 06:25:47  
Your compression and valves seem fine. Sounds like a classic case of worn valve guides to me. Do you get smoke at idle? That's when the intake manifold is at the highest vacuum and so you should see smoke also. The fix is new valve guides or finding a machine shop that can knurl your existing guides.



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J Schwiebert

05-26-2006 18:55:38




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 Re: Engine analysis needed here .... in reply to Way Up Here, 05-26-2006 06:25:47  
I will try again. Also remember you can have decent compression rings but the oil rings may be worn out. Rusty Farmall gave you the best advice on valve guides for a flathead engine. Kind of hard to suck a lot of oil up hill through the combustion champer. Did you check the clearance for the intake guides. How did it compare to specifications? J.



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Steven@AZ

05-26-2006 06:48:51




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 Re: Engine analysis needed here .... in reply to Way Up Here, 05-26-2006 06:25:47  
With the compression readings you got I would say the rings are OK. Sloppy valve guides will definitaly give you the blue smoke, especially a sloppy intake guide - because of the suction it's even easier to pull oil into the cylinder.



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dej(JED)

05-26-2006 06:30:34




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 Re: Engine analysis needed here .... in reply to Way Up Here, 05-26-2006 06:25:47  
The oil is getting into the combustion chamber from somewhere,probably down the vales guides.



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RustyFarmall

05-26-2006 06:37:12




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 Re: Engine analysis needed here .... in reply to dej(JED), 05-26-2006 06:30:34  
Worn valve guides on an overhead valve engine would cause smoking usually only on start-up. On a flathead engine it's a different story, the compression readings are relatively good, so I would say that those sloppy valve guides are the guilty party.



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