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Massey Harris & Massey Ferguson Tractors Discussion Forum
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Plug gap

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JAT

02-25-2007 11:20:43




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I have a MF 165 with Continental gas engine. I recently replaced the spark plugs and found 3 of the 4 were completly bridged with carbon. Today I had to move some snow and it ran VERY poorly so I pulled the plugs again. 3 of the 4 were wet with fuel, starting to build up carbon already and most alarming was that the gap had closed on those 3 plugs. The engine had only ran maybe 30 minutes since the plugs were changed.
What could be causing this?
Thanks.

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Grampa Leon

02-27-2007 07:07:33




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 Re: Plug gap in reply to JAT, 02-25-2007 11:20:43  
Am baffled to why plug gap closes by action of running,is it possible mice have built inside of engine?[by uncovered exhaust or carb inlet]
unlikely,however it has happened,so the following is suggested for you to try to eliminate another cause,remove exhaust pipe just prior to muffler,start engine,at a fast idle observe if any foreign material emits[also check
if muffler is plugged]also check if air cleaner is plugged or restricted[these two conditions inhibit excess carbon and soot]

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Grampa Leon

02-26-2007 14:53:46




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 Re: Plug gap in reply to JAT, 02-25-2007 11:20:43  
It is possible ,but not likely that carbon buildup is sufficiently stable enough to cause plug gap to decrease with out other symtoms,ie pre-igition and knock ,[if you are confident
carbon built up is the culprit,then I can suggest
a procedure to try]Also did you perform a compression test?



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JAT

02-26-2007 16:46:10




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 Re: Plug gap in reply to Grampa Leon, 02-26-2007 14:53:46  
I did not do a compression test. I'm not sure about carbon build up causing the problem but I do know there's a lot of carbon on new plugs and the gaps are closed. I'm not much of a mechanic so I don't know what could be causing this. I'm pretty sure the plugs are the right ones. I know there's spark getting to all the plugs. I can't imagine the valve timing could off because the cam is geared (right?)and can't jump out of time.
What else could cause this?

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Grampa Leon

02-26-2007 17:28:58




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 Re: Plug gap in reply to JAT, 02-26-2007 16:46:10  
Does engine backfire when it does run?[indicating
firing on an open valve,]camshafts are [as I recall] gear driven with a retaining nut.I would strongly urge the next step to be a compression test.In your first posting there was no indication of whether this gradually or suddenly became evident.[plug gap and fouling]



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JAT

02-27-2007 04:35:03




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 Re: Plug gap in reply to Grampa Leon, 02-26-2007 17:28:58  
No backfire.

>>In your first posting there was no indication of whether this gradually or suddenly became evident.[plug gap and fouling]

I'd have to say gradual. It wasn't running well for a while so I replaced plugs, wires, coil, cap, points, rotor, and even put on a new carb. Before that I can't really say when it went from good to not-so-good.

It still didn't run great after that but becomes worse the longer it runs.

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Grampa Leon

02-26-2007 07:21:22




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 Re: Plug gap in reply to JAT, 02-25-2007 11:20:43  
I interpet your original posting of plug gap being
"pounded" closed in operation,is this correct?{the reason I questioned plug type] if this is the case plug is too deep in head,I would suggest
adding another gasket to plug to eliminate this problem [temporarily],then I have some suggestions for your carbon build up.



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JAT

02-26-2007 09:32:36




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 Re: Plug gap in reply to Grampa Leon, 02-26-2007 07:21:22  
There is no evidence of the pistons striking the plugs but the gaps were closed. I wondered if there could be a heavy carbon build-up on the tops of the pistons that could push the gaps closed without the pistons actually striking the plugs.
Why else could there be so much carbon on new plugs with so very little run time on them, especially since there is good spark at all 4 plugs?



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Don-Wi

02-25-2007 18:39:29




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 Re: Plug gap in reply to JAT, 02-25-2007 11:20:43  
The operators manual says to gap them to .025.

Also gives these optiions for plugs:

Make of plug: std. hot cold
Champion D-16 D-21 D-14 AC 85 S. Com. 87 S. Com 83 S. Com.
Auto Lite BT-8 BT-10 BT-4

I would avoid champions at all cost and go with AC Delco or Autolites.


Donovan from Wisconsin



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Grampa Leon

02-25-2007 14:19:37




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 Re: Plug gap in reply to JAT, 02-25-2007 11:20:43  
Are you sure the proper plugs are installed,
and pistons are not striking them ?



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JAT

02-25-2007 16:44:58




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 Re: Plug gap in reply to Grampa Leon, 02-25-2007 14:19:37  
The plugs came in tune-up kit for a 165 with Continental engine and they are the same as the plugs I took out and showing the same problem.



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Grampa Leon

02-25-2007 17:18:37




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 Re: Plug gap in reply to JAT, 02-25-2007 16:44:58  
My source shows Atuolite 386 for your model 165,
is this correct?



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JAT

02-26-2007 04:44:54




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 Re: Plug gap in reply to Grampa Leon, 02-25-2007 17:18:37  
Yes, that's what I used.



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