#4 missing

Greg K · Aug 19, 2012

I have a 1950 M that has decided to keep fouling plug #4. I have switched the plug and wire with #3 and it still fouls #4 cylinder. The points are gapped at .020, the valve lash is set at .017,I don't know compression. When I pull the plug wire to #4 there is good spark, but with an intermittent miss that seems to only occur on #4. What are my possible problems here? Also what size not Champion plugs should I get for it?

Greg K · Aug 19, 2012

Forgot to mention cap and rotor are a couple years old. The tractor mostly sets inside and gets used mostly for moving snow.

rustred · Aug 19, 2012

next step... check compression.
that will give engine condition, may have valve problem.

Brownie 450 · Aug 19, 2012

Have you had the #4 plug out? Pull it & check for carbon particle or other foreign matter bridging the gap. Could be a bad plug which needs replaced.
Autolite 386 or equivalent.

Janicholson · Aug 19, 2012

Fouling a single plug can come from either a valve stem that is passing substantial oil into the intake, or rings that are letting it get on the top of the piston. Iven a good compression reading can blind a person to a stuck or broken oil control ring. If it were mine I would watch for blue smoke when pulling hard for 20 minutes, indicating rings, or blue smoke idling, or when coasting down hills, or at startup. Continuous blue is likely rings, intermittant is likely valve stem oiling. If in doubt put on a set of Umbrella seals, or Perfect Circle style valve seals to see if it corrects the fouling. No need to remove the head, Search the archives for -- rope to hold up valves. Jim

Greg K · Aug 19, 2012

It has the usual valve seal problem of a large puff of blue smoke when it starts up. I am not very confident of the condition of the motor either. I have a compression tester that has probably never been used, what is the proper way to use this? I have used it before but I want to make sure I am doing it right too. I didn't see any umbrella seals for the valves on the tractor parts page, do they make them? I just started my own business this spring so I'm kinda broke right now and I can't afford to throw alot of money at it right now.

rustred · Aug 19, 2012

pretty easy, screw it into the plug hole, open throttle and give er about 5-6 cranks of compression and watch the guage. do the same for all cyl's. an engine in good condition the compression will rise to max. in about 2 revolutions.thinking around 100-120 psi for that engine. if they are within 10 percent of each other its good. zero or real low is valves. even and low could be rings, for this squirt some oil in and recheck and compression should raise.
they dont come with valve seals,thats an add on when valve job is done.

gene bender · Aug 19, 2012

I purchased a B that had two pushrods out of the rocker arms. I installed them and set the clearence compression test showed those two cycls low which i expected. used the tractor and after changing and cleaning new plugs the problem because of missing finally they began to fire better and better. Now the compression is even with other cycls engine starts and runs fine with a little smoke but it runs just fine and gets used for odd jobs nothing heavy.I would sugest setting the clearence and keep changing and cleaning plugs and the problem just mite go bye bye.

Greg K · Aug 19, 2012

OK checked compression and it is around 100# on all four. I guess I will start looking at valve seals, maybe hook the air hose up to the spark plug hole to hold the valves up and just pop the retainer and keepers off and put an umbrella seal on. Thanks for everyone's help

rustred · Aug 19, 2012

ya, sounds good. then take it out and work it under load for a few hrs. seen lots of these tractors foul plugs just idling around the yard with nothing to do. thats what happens when they never get to operating temp.

Angle Iron · Aug 20, 2012

Dad set the carb under a load to run and pull the load the best. That M would do a good job. It would on the other hand give trouble on light loads and loader work if not reset. What I am saying is you may want to lean it out a little and see if that helps.
Angle Iron

#4 missing

Greg K

Well-known Member

Greg K

Well-known Member

rustred

Well-known Member

Brownie 450

Member

Janicholson

Well-known Member

Greg K

Well-known Member

rustred

Well-known Member

gene bender

Well-known Member

Greg K

Well-known Member

rustred

Well-known Member

Angle Iron

Member

Similar threads