B piston in spark plug hole

[mrnecks]

I have been working on my B John Deere for a couple of weeks now mostly on carb and governor issues. Then it wouldn't crank last night and I noticed that one of the pistons covers nearly half of the spark plug hole. Doesn"t look good to me but not sure what or why? Any ideas are appreciated.

 

[Mike M]

What era B ? Someone could have missmatched parts in there trying to boost compression ?

I had a late B with the pressed steel frame and noticed that on one side. Someone put the piston in rotated upside down so the spark plug relief cut was not in align with the spark plug hole. I was able to take off the inspection cover unhook connecting rod and rotate it around to the correct spot.

 

[mrnecks]

Its a 1948. It would run but while attempting to start it last night it backfired really loud and then never attempted to start again.

 

[toot]

If like mike said and the piston is not aligned correctly that would be the problem. However depending on whats in there, if some one used a taller or custom piston to boost compression, you should still be fine. One of my previous pullers had pistons that almost covered half the plug hole, still started and ran very well.

 

[mrnecks]

That makes sense. Why do ya"ll think I"m getting such a bad backfire? Its like a shotgun going off. Think I need to look into valves?

 

[Resting Relics 1]

Sounds to me like you may have your spark plug wires crossed coming out of the mag. Just a thought. Not sure how and where you are in this problem. Did this problem just all of sudden start or did you work on it and now this problem is showing itself.
John

 

[Mike M]

Easy enough to get that cover off and look at the back of the oistons for casting numbers.
Are both yours covered or just one ? if one it is most likely just flipped like the one I had.
Flip it over just to make sure it is not a problem even though you may have other problems.

The one I bought Had a history of crankcase explosions that would blow the valve cover gasket.
Only thing I found wrong with the tractor was that one piston flipped. Was that it ? I don't know. It found a new owner and other then needing a head retorquing I never heard any more from him. The guy that put the piston in wrong must not of retightened the head nuts as they were loose too and it started to seep antifreeze.

 

[mrnecks]

Tractor had been sitting for 10 years so I'm trying to get it running. Had it running but the governor wasn't working and it wanted to run to fast . I think I have that fixed but now the issue of it not cranking has started and it kind of acts like one valve isn't opening.

 

[RandyB(MI)]

Just a little note on the backfire you heard, if it has the original ign then it has a mag which will fire on the exhaust stroke and when flooded will have a tendency to fire the excess fuel pushed out in the exhaust and it will be one loud bang. Might not even be related to your real problem but your problem creates the flooded issue.

 

[strokerb]

Sounds to me like a stuck valve. Is it back firing thru muffler or air stack? Also make sure no critter crawled into air stack or pre cleaner assembly and plugged it up. Pull valve cover and make sure all rocker arm and valve are moving properly.

 

[mrnecks]

It's through muffler.

 

[Machinery-Man]

I suppose someone could have put the pistons in upside down, not leaving the notched space for the plugs...I've heard of this....you could borrow one of those mini cam cables and look inside the cylinder as t design of pistons...I don't like the idea of the piston covering part of the hole as this may make for incomplete combustion...for my own personal prefer stock pistons cast iron to get the proper timing burn time and torque.

 

[Resting Relics 1]

Hey,
I don't think it would be a stuck valve because if the valve is open it won't have any compression in that cylinder and thus won't fire enough to make it backfire. Should be able to do a quick check by just holding your thumb over the spark plug hole and crank it over. You should be able to feel some compression. I'm guessing you have compression but somewhere there is a timing or some type of ignition problem. If its backfiring your getting gas and spark just not at the right time. Good Luck!
John

 

[buickanddeere]

Weak valve spring? They do sit with the valve always open and the spring squashed.

 

[mrnecks]

I may see if I can rent one of those cameras at the parts house, I could just sleep easier at night knowing the answer. Sleep even happier if I don't have to buy another head gasket.

 

[rick deere]

change wire at mag or distributor try to state you have nothing to loose all to gain, put them back if it dont work.

 

[mrnecks]

I swapped them and it cranked so I must have turned the mag a turn and didn't realize it. I do feel dumb for that part but all the help about why I am seeing the piston is very appreciated. I have a camera coming tomorrow so I can get an answer.

 

[rick deere]

Leave it alone if it runs thats all you want,glad to have helped you and thanks for trying what I said.Been there done that many times.