burned piston

[coop1954]

i asked on here if a piston i replaced would last,someone said if i corrected the original problem it would. any thoughts on why the bottom piston in an inline 3 cylinder would burn,,not bothering the other 2 at all? plug indicated overheatingin that cylinder only.

 

[mikesea]

Re: burned piston

my first guess would be dirty carb

 

[Silvertip]

Re: burned piston

The plug would not indicate overheating but it certainly would indicate a lean condition. As would the piston itself. Lack of lubrication is not the issue as that cannot be cylinder selective. However, lubrication must pass through the carb so if you had a carb running lean on that cylinder, it also doesn't get a proper dose of lub so it goes "poof". If the cylinder isn't scored and measures within spec, replace the piston and rings, rebuild the carbs (all of them) and go.

 

[ezeke]

Re: burned piston

In addition to the possibility that a fouled carburetor could cause the cylinder to run lean, an air leak could do the same, as could a leaking fuel pump membrane.

 

[bob johnson]

Re: burned piston

The plug would not indicate overheating but it certainly would indicate a lean condition. As would the piston itself. Lack of lubrication is not the issue as that cannot be cylinder selective. However, lubrication must pass through the carb so if you had a carb running lean on that cylinder, it also doesn't get a proper dose of lub so it goes "poof". If the cylinder isn't scored and measures within spec, replace the piston and rings, rebuild the carbs (all of them) and go.

so...a three cyliner with three carbs does not get fed its fuel mixture soley from a SPECIFIC carb??

do all the carbs dump into a "chamber" and supply all cylinders equally??

I had thought that each carb basically fed a specific cylinder....

is that not true???

bob

 

[jonesg]

Re: burned piston

so...a three cyliner with three carbs does not get fed its fuel mixture soley from a SPECIFIC carb??

do all the carbs dump into a "chamber" and supply all cylinders equally??

I had thought that each carb basically fed a specific cylinder....

is that not true???

bob

true far as I know, some 3 cyl's might use a common single carb.
Clogged carb jets or air leak are the common culprits.
What was the compression reading before you tore into it?
That would tell you a lot.
A loose sparkplug can be a problem, had that happen to me.

Air leaks cause over-lean running, thats the same as an over advanced ignition , then pre-ignition starts and the combustion chamber goes over the melting point of alum. Whats that, 1200degs? Not much.

If you can't track down the cause use an infra red thermometer to ensure the lower cyl is actually firing after rebuilding engine and carbs.
I would re-plumb the whole system.

 

[bob johnson]

Re: burned piston

true far as I know, some 3 cyl's might use a common single carb.
Clogged carb jets or air leak are the common culprits.
What was the compression reading before you tore into it?
That would tell you a lot.
A loose sparkplug can be a problem, had that happen to me.

Air leaks cause over-lean running, thats the same as an over advanced ignition , then pre-ignition starts and the combustion chamber goes over the melting point of alum. Whats that, 1200degs? Not much.

If you can't track down the cause use an infra red thermometer to ensure the lower cyl is actually firing after rebuilding engine and carbs.
I would re-plumb the whole system.

jones, I wasnt the OP, just read some info that i hadnt known and asked about the carbs feeding specific cylinders.

if there exists a timing problem, wouldnt that apply to all the cylinders??

I am trying to get a grasp on what the forum is saying might be the cause of a SPECIFIC cylinder going bad.. and the other two not having any damage or apparent issues!!!

up to this point I was thinking a bad or clogged carb could lead to a SPECIFIC cylinder going bad

bob

 

[Dhadley]

Re: burned piston

Several things to look at. Yes, carbs first. Each of the three carbs feeds a specific cylinder. The bottom carb feeds the bottom cylinder. There are 3 cylinder motors with one carb but your motor isn't one of them.

Where is the piston damaged? In the middle of the dome? On the edge right by the exhaust port? What spark plugs are you running?