221 cu in 1939 Failed No4 Piston 1

[Phil Gillespie]

See a few pics of the reason my No4 Cyl was not showing any compression.
Engine is 221 with 80 thou oversized piston.


The reason for this? These pistons have possibly 9 to 10 thousand miles max.
On the plus side, head, Edelbrock is unmarked, bore on this No4 is also unmarked. Intention to remove piston, identify and just get one and a set of rings and refit. However still running the spit valve guides and thinking of maybe replacing as suspect some oii usage is due to valve guide clearance.
When I got it home after a test run whe this happened, couple of good clouds of smoke into compartment. I took a set of compressions next day when cooled down .
!: 140. 2:135. 3: 132. 4: Zero!! 5: 120. 6:120. 7: 115 *: 100.
So figure to check valves at No4 as well as getting hold of a replacement piston and rings. Hope to do this in place wth engine in car.Should be possible?




You just have to move on and attend to it.
Phil NZ

[Talkwrench]

Ahhh geezus... Better talk to Brian he may have some insight..

[GEOFFNZ]

Hi Phil.That is not good.Any sign of the piston hitting the cylinder head,Geoff

[Phil Gillespie]

Nope Geoff as the cylinder head is in good order.The pic is of that section of cylinder head above No4 piston. Only idea I currently have is this piston No4 & No1 had a problem with spark plug gaps closing up to almost nothing. Hence combustion would not have been good. Maybe some carbon build up.
I eventually ended up putting an extra seal washer on both spark plugs and they then retianed the spark gap and plugs as checked were a nice tan colour. Previously were showing slightly oily dark.
Once i get the piston out will then begin search for a piston and rings.
These type of valves with the split guides will come out complete once valve guide retainer is removed?
Phil NZ

[flatheadmurre]

The guides will come out in one piece...and hopefuly without to much bad language.
A K-D valve guide puller is your best friend for that job.
Since thoose pistons aren´t ford finding a weight matched couple might be a challenge...you can just cut so much weight off and if they are heavy slugs it´s even worse.

[Phil Gillespie]

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Ok so I can remove, hopefully if all is free, the complete valve and spring, and retainer, by just removal of the horseshoe and then dismantle valve out of engine. These being split guide with mushroom at valve stem? Yes.?
Phil NZ

[Ggmac]

Did a spark plug electrode let go ?

[51 MERC-CT]

Don't remember ever seeing registration marks on top of the pistons that big and deep. Look almost big and deep enough to alter the compression ratio.

[Ggmac]

Ok , how much nitrous did you use ?

[tubman]

This may be completely unrelated, but the last time I saw something like that was on a snowmobile we were racing. The leaner you get 'em, the faster they'll go until something like this would happen.

[flatford8]

There doesn’t look like enough carbon to cause a plug gap to change. ( If I read the post correctly)....:Mark

[marko39]

if valve and guide wont come out as an assembly, pry up spring and remove retainer and then spring. lift valve and tap out guides with a thin punch. take care not to bend spring too much unless you have a spare.

[Admiral]

Sorry to hear what happened! I wonder what the culprit could be, as everything is pretty spotless in there. Carbon buildup wouldn't be my guess.

[JSeery]

If it was me, I would be looking for a set of 8 new pistons.

[Mart]

Would I be completely off base by thinking, if it were me, If I could find a piston, I'd reuse the existing rings? In my mind, the rings are bedded to that bore equally as well as the other 7 piston/ring/bore sets.

It does beg the question, though, why did that one let go? If due to lean mixture, there should be 3 other pistons that might have been getting fuel and air from the same side of the carb. (Assuming single carb). If it is a defective piston, what is to say the others are not on the verge of letting go?

If you can find one piston, all well and good, cross your fingers and carry on. If not it might be worth going with a new set of pistons and rings and a freshen up of the bores with a hone to seat the new rings, or go .100 over on all 8 with a new overbore.

Personally I'm a chancer and would just change the 1 if a replacement could be found, but that might be the clincher. You might not be able to find just 1 and be able to weight match it to the rest.

Good luck with it, though.

Re the valves, you should be able to pull the guide(s) down with the correct tool and withdraw the whole assembly in one go. Remember on the inlets it is often easier to push the guide down with a suitable lever.

You push the guides down just a bit to get the horseshoe clips out.

Mart.

[alanwoodieman]

if the gaps on the plugs are closing then- too long on the reach of the spark plugs--exam the sparkplug thread area- have they been counterboared? we have used double seal rings on several spark plugs used with aluminum heads to correct this reach

[40 Deluxe]

Could be #4 went lean. check the intake gasket. If it's an aluminum intake, check the exhaust crossover passage for burn through. I'm not sure which cylinder(s) this would affect, but worth checking. A closed-up plug gap wouldn't cause this. A weak or no spark would make that cylinder run cooler, and this is an excessive heat problem.
Also, could two plug wires have been crossed? This could cause extremely advanced timing in #4, resulting in detonation.

[JSeery]

Very hard to tell much from photos, but that piston and cylinder head doesn't look like it has been that hot. That coupled with the overall look of the pistons (they look like low quality, but again based on a photo!), I would suspect piston failure. It could have been a detonation issue, but the piston seems thin in the failed area. The amount of work involved finding a piston and getting it to match weight wise, etc, it would be simpler to just replace the lot. But then, that is what I would do.

[Phil Gillespie]

Yes Alanwoodieman that was the case with these Edelbrock heads the 2 plugs in 1 & 4 wennt too far into the head. These were new heads with this finish! Made offshore and not as would expect. That was why i fitted extra washer at those 2 cylinders to reduce distance into combustion space.

[Seth Swoboda]

His pistons look like mine. Mine are Egge. I would assume Egge has a good quality piston.