Topic: #3 cylinder write off - oil everywhere-'72-350F

[FuZZie]

Seanbarney- is there a reference or technical comment somewhere that discusses this issue |(do you know?)
FuZZie...  "use a little" what on #3?

oil, and I'd doubt any doc is available. I've just never seen a sparkplug that far out that was still attached.

[seanbarney41]

Yes,  so I  think you are saying the fuel is washing the cylinder and not combusting (?)   .... but would that mean oil goes past too?  I dont know enough about whats happening in the suck, push, bang, blow process to know if there is an opportunity for oil to run into the pipe in that situation.   comments?.

I'm not sure, really you should hang in for someone more knowledgeable but I'm thinking you were running pretty much on 3 cyl.  So you may have been seeing something like any gas and oil in #3 getting blown out the exhaust unburnt, mixes with the carbon in the pipes then you see black oil like liquid come out the pipe.
Also have you been noticing any oil loss when checking the dipstick?

I think Fuzzie's got it here, plus all kinda crankcase gases and extra heat are gonna be created in this situation causing oil and smoke to puke out the vent tube onto the rear tire.  Basically, you need to re-check all your engine clearances (piston, cylinder, valves, guides, seals, valve seats), fix anything wrong here and then the only thing left is that #$%*ed up spark plug thread...yeah, I have never seen this problem before.

[Jim]

Ok.. this is extremely helpful then.  The valves are seated well and have new valve guides to install. the jugs in the shop for de-glazing and I've new rings on the way. machine shop will ensude thread in plu hole is clear and proper depth ... I'll put it together with clean carbs and give it a try with my fingers crossed; I hope that's what it was . thanks for the reassurance.  J

[ADW]

I'd think also that cylinder #3 would be way down on combustion pressure with that spark plug out that far (remember this is a 350F, pistons are pretty small). The combustion volume of that cylinder is probably almost doubled with the plug out that far, halving the compression ratio for #3. The mixture sure as heck wouldn't burn right or on time under those conditions.

[Jim]

So it would be fuel and oil laden when it exhausts in a cooler state?               It's begining to make sence to me.

[seanbarney41]

I'd think also that cylinder #3 would be way down on combustion pressure with that spark plug out that far (remember this is a 350F, pistons are pretty small). The combustion volume of that cylinder is probably almost doubled with the plug out that far, halving the compression ratio for #3. The mixture sure as heck wouldn't burn right or on time under those conditions.

that's a good point that I had not thought of

[ADW]

So it would be fuel and oil laden when it exhausts in a cooler state?               It's begining to make sence to me.

Yes. It may be igniting VERY poorly, if at all, under those conditions.

How can that spark plug be so far backed out? Is there a stack of old plug gasket washers underneath it that somebody just kept piling a new plug onto it?

[Jim]

i left it at the machine shop to take out the valves and havent looked really closely in that spark hole.  they'll clean it out and clear the thread and let me know .. I'll post it when i go pick it up. 

[FuZZie]

Could have been a bad Helicoil or similar the PO installed ADW.

Sounds like you have all the bases covered Jim, let us know if they find anything else and please add a pic of the repair before you close it up. Could help someone searching down the road.    

[JimD]

10-4... thx  for helping 
I'll need to wait until the parts come in to conculde this in a week or two but will do (and expect to pass you on the trail to Ingonish ;-) his summer)  J

[FuZZie]

Well your welcome to try! Pm me this summer if you do decide to ride the trail, if timing permits I'd love to join up for the ride.