[deboo3]

I dont know what happened exactly, but here's the story. This weekend I readjusted the roller rockers on the 460, the 5-8 side only. Made sure it wasn't more tight that 1/2 turn after being handtight. Today I went for a cruine and of course there came a moment full throttle felt like the right thing to do When I hit 4000 rpm I heard a rattle and immidiately held back. The engine kept running, the rattle went away and I got home asap without getting the engine of 1500 rpm. Luckely it was 1 mile away form home. No that the engine ran good than before

First I checked to see if the roller rockers were still tight, which the were. Then I went to check the sparkplugs and noticed that disconnecting nr 6 didn't make adifference in the engine performance. I took the plug out and noticed it took a hit. The gap was zero. I replaced the plug with another one and the engine doing fine. So far.

What could possibly hit the spark plug to make it bend like it did?

 

[557MAV]

r u or were you missing anything around the carb at any time,washer, carb nut, squirter screw.

bump plug prior to install

bring the piston to the top and shine a light in it and see if you can see any damage to piston.

 

[deboo3]

I can't recall missing any parts that could've gone through the carb. Fact is that I have a rattle in my engine I can't get rid of, even prior to the above discribed issue. Last year october the heads went off, butnothing in the chamber, but a rattle indeed. Could be related to the spark plug issue or not. anyway I'll try to look into the cylinder through the sparkplug hole and check.

 

[crittersf1]

Wrist pin rattle?

 

[Dirtybird545]

detonation?

Whats your c/r and timing.What octane fuel?
Russ

 

[mysticowner]

I would bet the top is starting to come off that piston. Better look
real good around the outside edges.

Been there done that. I wish you luck.

 

[deboo3]

Well the rattle is not always there. I'm pretty sure it's related to the rockers since it sounds like it's coming from under the valve cover.

Concerning the spark plug that took a hit, well I've driven the car frequently ever since, but without excessive WOT actions, I'm afraid something will happen It's been doing fine fortunately. Let's hope inspection through the spark plug hole will make things clear. Engine is pretty new, so broken pistons is not someting I expect, but how knows.

I did a compression test the other day and all cylinders were between 13.5 and 14.5 bar.

My c/r is 10.5 and timing is set to 14 degrees advanced. I run on LPG (Netherlands)

 

[bosshoss]

What spark plugs are you running? With your compression ration etc it seems unlikely but I have seen plugs get whacked shut by the piston when the engine is revved before. Sometimes just paying attention to where the electrode is facing in the combustion chamber helps, If you are running a projected tip plug you could try one of the shorter versions.

Do you know how much piston to wall clearance you have? Not sure on the burning temp of LPG. Is it much lower than gas? If so could you be experiencing lots of piston rock due to the pistons never heating up enough to fill the bore?

just rambling here pulling stuff out of the air.

dkp

 

[gafred99]

do a leak down test on cylinder in question then do rest and compare #s.

 

[crittersf1]

I would bet the top is starting to come off that piston. Better look
real good around the outside edges.

Been there done that. I wish you luck.

Find somebody with a bore-scope and look real close. If indeed the gap was closed the piston is most likely coming apart.

 

[deboo3]

Find somebody with a bore-scope and look real close. If indeed the gap was closed the piston is most likely coming apart.

I haven't had a chance to have a close and good look. I haven't had a problem eversince, but I'm still taking it easy an haven't had much full throttle action lately. But can somebody tell what can cause a piston coming apart, a lean mixture maybe?

 

[crittersf1]

Lean, over-heating, in-correct ring end gap.

 

[Mark Laczo]

Rattle

If you heard a rattle it could be detonation (top of piston flaking off) Most of the time with LPG or propane you cannot hear detonation. I have heard it on one of my engines once but I was at around 12-1 with a really small cam. Propane is hard on exhaust seats. I think it works opposite of gas rich will raise combustion temp instead of lean. What system are you running and do you have any sensors like a O2 or anything. Looking at top of piston will tell the tale IMO.

FWIW Mark

 

[rmcomprandy]

I would bet the top is starting to come off that piston. Better look
real good around the outside edges.

Been there done that. I wish you luck.

Yea ... I would speculate that the top ring land is burning or breaking off the piston(s).

NOBODY detonates anything ... of course the signs are usually there to tell a different story.

 

[mysticowner]

If you plan on keeping that engine you should probably pull that head sooner than later. Don't wait till you destroy the head too.