Burned down a piston

mwking · Post by **mwking** » Thu Jan 22, 2009 10:15 pm

Hi,

I went out for a ride last night on the '82 Trailfire that I rebuilt over the summer. It was running fine and I was opening it up pretty good once in a while. The only thing I noticed was that if I really got on it I could see the end of the muffler through the vent start to glow. I almost made it home when the pto side piston had a meltdown. I only had 160 miles or so on the rebuild. I had been keeping an eye on the plugs and they were both a nice brown colour. Now the pto side plug is nice and white. I pulled the motor and did a pressure test and it seems ok. The only trouble I had was a leak around the exhaust manifold on the pto cylinder, I put the metal shroud part and gaskets back in with the block off plates and that seemed to stop most of it. I wouldn't have thought that a leak in the exhaust would cause any problem but I am really wondering what went wrong. I have attached a pic. The Pto cylinder has a steel sleave in it. It was honed and the piston reused. The flywheel side was replated and has a new piston.

Thanks,

Murray

Attachments:

DSC00803.jpg (850.05 KB)

Rodimus Prime · Post by **Rodimus Prime** » Thu Jan 22, 2009 10:52 pm

do you have a better picture from ontop cause at this point it looks just like you installed the piston backwards type burn out. Or were running airplane fuel one of the two.

mwking · Post by **mwking** » Fri Jan 23, 2009 12:15 am

You can't see the E and arrow because there is quite a bit of top of the piston melted away on the exhaust side. I am running 91 octane premium gas.

Murray

big danno 1970 · Post by **big danno 1970** » Fri Jan 23, 2009 1:47 am

What is the condition of the fan belt? Is it loose? looks like it got really hot judging by the discoloration of the fins on that side compared to the other or maybe thats just a shadow.

mwking · Post by **mwking** » Fri Jan 23, 2009 10:01 am

The fan belt is pretty tight. I replaced it when I rebuilt the motor, it has probably stretched a little but I can't see that it would slip. The difference in colour of the fins is because the flywheel cylinder was cleaned up before it was replated, it looked like they sand blasted it. The pto cylinder is not as clean.

Murray

Post by **ICCSF 108** » Fri Jan 23, 2009 10:39 am

I don't believe the muffler would/should be glowing I would look for either a loose baffle in the muffler (shaking it should let you know this, or possibly that a mouse has it partially plugged with either a nest or food of some type?? )
Also this is only my opinion but I don't think I would mix a chrome cyl. with a steel lined cylinder especially on a single carburetor machine, I don't see how you can possibly jet for the difference in expansion..

Kenny

mwking · Post by **mwking** » Fri Jan 23, 2009 4:27 pm

I might have just stumbled onto something. When I rebuilt the motor this cylinder and piston were good and I reused them. I noticed that the cylinder head had some pitting from a previous piston failure. I swapped on another head that looked better. Now that I have them side by side I can see that they look a little different. Kimpex lists two different part numbers for pistons for the Trailfire. Anyone know if they changed compression etc.? The original head is on the left in the picture, the one that was on it when it failed is on the right.

Murray

Attachments:

DSC00805.jpg (830.93 KB)

Rodimus Prime · Post by **Rodimus Prime** » Fri Jan 23, 2009 10:53 pm

kimpex lists the pistons with different sizes ie if you bored over. They also list a different piston for liquid engines because liquid engines have different clearances. both heads are functionly the same. left is from a cat engine about late 70s. If piston was installed correctly then look for a split base gasket or mating surface causing an air leak. Sometimes sleeved cylinders dont have good sealing surfaces check with sandpaper on a plate of glass for minor warpage on both cylinder or head.

Both cylinders will warm up differently and pto wear the rings a bit faster.

The damage done shows the piston melted towards exhaust side meaning it got unusally hot. Alot of aluminum disappeared somewhere probably into the muffler leaking exhaust wouldnt do that to just one cylinder on these engines. Lean would be in center of piston. Something to check is camfer of ports while i doubt it its possible the top ring cracked early by catching on exhaust port this creates a hot spot but no real noticable loss of power because of second ring.

In your pics i noticed that you put gaskets on dry... bad idea use aluminum paint install gaskets wet. ( you can buy the more expense copper coat sealant but it does the same job )

At this point get new piston clean up cylinder check camfer of ports ( slight angled edge on port to allow piston rings to slide by) check cylinder and head for warpage. reinstall everything torgue heads once to spec, wait 5 mins check torgue again install engine into sled warm up good retorque heads when cooled install covers. Run engine under normal conditions DO NOT GO FULL THROTTLE for at least first 50 miles on new piston or rings. Check exhaust tempurature occasionally on y pipe it should not vary much from side to side ( yes you can do it with your hands i would advise leather gloves though, or you can buy a laser temperature checker now for about $20)

If your worried about exhaust gaskets the old trick was to use high fiber grease on gaskets and surfaces ( oil would burn off but fibers made good seal) or the gray slime exhaust sealant.

fordmtrsp · Post by **fordmtrsp** » Sat Jan 24, 2009 1:11 am

did you put different rings in the cast iron sleeve to my knowledge you need to the normal ones that you put in a chrome bore will not seat on a cast iron sleeve maybe why you had so much heat.

80_liquifire · Post by **80_liquifire** » Sat Jan 24, 2009 12:26 pm

Not to change the subject .

Can you reuse head gaskets,that is if you did not use a sealent on a new set ?

Rodimus Prime · Post by **Rodimus Prime** » Sat Jan 24, 2009 12:40 pm

80_liquifire wrote:Not to change the subject .

Can you reuse head gaskets,that is if you did not use a sealent on a new set ?

Your not supposed to. However scuff the headgaskets with scotch pad/steel wool throw on paint install wet torque down and have fun. Advantage is old headgaskets dont shrink aka dont usually require a second or third torqueing. Done it on many engines over the years with good results. If head gasket shows any signs of bad leakage, gouges, or blowout dont reuse.

mwking · Post by **mwking** » Sat Jan 24, 2009 7:56 pm

I did not change the piston or rings on that cylinder. From what I have been told the sleeve will wear them out faster, but they should be ok. '80_Liquifire if the head gaskets are in good shape you should be able to reuse them. I wouldn't use them if you are unsure how old they are, if you have any doubts replace them. Rodimus Prime I have read your post carefully two or three times, lots of good advice there. I am going to go through the motor carefully and hopfully things will go ok this time.

Thanks,

Murray

80_liquifire · Post by **80_liquifire** » Sat Jan 24, 2009 8:05 pm

Guys Thanks,
the gaskets are new, I only ran the engine for about 15 minutes tops at idle.
Have not takin it out for a spin yet. I did put them on without any dressing , just wondering if it would be better at this point to break it apart now and use a sealent .
It runs good and I retorqued the heads already .

Post by **ICCSF 108** » Sat Jan 24, 2009 9:29 pm

If it's not leaking water now ( If working on a Liquifire), If a fan, Free Air or Liquid then run it for a bit more then re-torque again.
If you keep messing with it you might as well put new gaskets in..
Kenny