140 Evinrude '83 Burnt #4 piston

evarnad · #1 March 17th, 2003, 05:22 PM

I have a rebuilt '83 140 Evinrude with a burnt #4 piston for the second time. Was told it could be an ignition problem. Anyone have the same problem ? Engine ran fine during break in but would have a bump or miss at above 4000 rpm, I would back it down and it would run fine unitl I get it to 4000 rpm or above, held it there for a few seconds and that is when the piston burnt. I would agree with the ignition problem but could it be getting air through the lower crankseals ? I know these engines have had piston problems in the past but the new style pistons should have taken care of it. Help anyone

clanton · #2 March 17th, 2003, 11:39 PM

The only thing wrong with this engine is the rebuilder and powerhead installer. Orignal pistons ok. After rebuild I would replace both power packs, mark fly wheel and check timing all 4 cylinders at 5000 rpms in water in gear. Do not forget to replace the water deflectors in the block.

Dhadley · #3 March 18th, 2003, 03:35 AM

Ditto. There is nothing wrong with the basic design nor the pistons. A burnt piston is a RESULT of something NOT the CAUSE!

Whatever caused the first failure was not corrected. I would follow Clantons suggestion about marking the flywheel and checking for a double firing situation.

Actually if the motor still runs, now is the time to grab a test wheel and figure it out.

Good luck!

evarnad · #4 March 18th, 2003, 02:21 PM

Thanks for the info. Can you give me the steps for doing the timing of all four cylinders. Do you mark the flywheel at TDC for all the pistons. Whats the best marking device. Could there also be a problem with the componets under the flywheel. Any more information will be welcomed.

Thanks again

Wayne

Hooty · #5 March 18th, 2003, 04:42 PM

Roger marking each piston at TDC.

c/6

Hooty

Solittle · #6 March 18th, 2003, 04:55 PM

evarnad - Do your self a favor and get the OMC manual specific for your motor. I have had a number of OMC V4s over the years and never heard of piston problems. I think you are getting some bad info. It takes a lot of work to break those 140s.

tbroussard · #7 March 21st, 2003, 10:30 AM

There was a problem with the original pistons from OMC. The ring grooves were made too close to the crown of the piston. At high RPM's the ring had a problem that it would break though the piston from the groove that was only an eighth of an inch below the crown of the piston. The fix for it was to buy all new pistons that had a revised update made to the piston putting the groove lower and with more meat above the piston ring groove.

Good Luck.

Dhadley · #8 March 21st, 2003, 11:32 AM

The problem was not the old high ring piston itself but when the fuel changed or the motors were lugged or over propped then damage would occur. The race guys used them for years with great success.

Good luck!

evarnad · #9 March 21st, 2003, 02:46 PM

Thanks to all for the replies about the piston problem but I would guess that I have a ignition or a lean mixture problem. I'm leaning towards the ignition, can anyone one expand on the test procedure.

PS I guess the race guys can afford to go into their engines often and run race gas, but I don't have that luxury.

Thanks Again

Wayne

Hooty · #10 March 21st, 2003, 04:41 PM

Put a mark on the flywheel for each piston at TDC. Put a timing light on sparkplugs nr.1, nr.2, nr.3 & nr. 4. Each one should fire once close to its corresponding mark on the flywheel.

What you're looking is nr.4 firing twice, two quick flashes.

c/6

Hooty

Dhadley · #11 March 22nd, 2003, 06:26 AM

It would help to know more about the motor. Is the piston burned in the center or on the top edge near the exhaust port? What spark plugs? How old was the fuel? What grade? What is the top rpm? How are the sides of the pistons?

I'm still thinking of a double firing situation and would, if it were me, degree the flywheel and check it at the 4000 rpm you mentioned while concentrating on #4 with the timing light.

Keep us informed!