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Noise in Russian Mopar L-head


Cpt.Fred

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Some of you might remember the pictures of my friend's russian GAZ M20 Pobieda which is powered by 30s Mopar technology.

The engine is said to originate from the Dodge D5 L-head and was on duty in a russian scout tank.

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notice the changes that where made to the ports!

or is that the same on the early l-heads?

the D5 was a 36 model with a 218, right?

on a trip a few weeks ago he overheated the engine on the motorway,

he was travelling in the dark and didn't pay attention to the temp gauge

which is illuminated quite poorly. he noticed a tapping noise from the engine bay,

stopped the car immediately and found he had blown the head gasket and warped the aluminium head.

he has fixed that by now, but when he restarted

the engine after the head repairs the tapping noise was still there.

he says it's heard best from the underside, near the rear main seal.

does anyone have an idea what he could be dealing with?

i know it's always difficult to say, but any help is greatly appreciated...

best,

fred

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I think it might be wise to drop the oil pa and have a look at the rod and main bearings.

The other posibility depending on how hot it got ( was it close to siezing) is a distorted Piston/s that is now slapping against the cylinder as ti goes throug it stroke. The noise could be louder under load and associated with when that cylinder fires. You clould try runnig it and pulling the plugs wire one at a time to isolate the source of the noise.

Guse its not the fuel pump as I see a block off plate in place for the stock pump.

Edited by greg g
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Regarding Greg's post, when my engine was making its mysterious rapping sound last summer, the overheated/distorted piston theory was the first thing my machinist suggested. He thought the block might have developed an air pocket around #6 cylinder, allowing it to overheat in that spot and distorting the piston. It turned out not to be, but that was his first thought.

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thanks!

the noise started with the overheating and it is my understanding that he stopped

when he could first heard it. when he checked the gauges he saw the temp way up,

and the radiator got so hot the solder melted in some places. there wasn't any water left in it, so i guess it must have been REAL hot.

when the head was off there was no damage to be seen on the inside of the cylinder walls, pistons looked fine.

he's currently checking if he can take the pan off without removing the engine.

what about wrist pins?

i remember reading something about them being a weak spot...

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a wrist pin noise would also be associated with the cylinder firing. Again pulling the spark plug wires one at a time withthe engine idling might also isolate the effected cylinder. The noise will not be there when the cylinder is not firing.

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thanks!

the noise started with the overheating and it is my understanding that he stopped

when he could first heard it. when he checked the gauges he saw the temp way up,

and the radiator got so hot the solder melted in some places. there wasn't any water left in it, so i guess it must have been REAL hot.

...

The melting point for soft solder such as is used in radiators is over 360 degrees F. Doubtful the radiator ever got that hot. Also if the temperature gauge was reading very hot then the probe had to be sumbermeged in water. The probe will not read hot air with any accuracy.

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don, the radiator must have had several leaks around soldered parts when he refilled it that weren't there before,

so he told me he thinks the solder must have partially melted.

i don't know how he hooked his temp gauge,

but i know he has at least one more feeler he uses for oil temp and another one

for controlling the electric fan he put in.

unfortunately i can only tell here what he tells me, but he is an experienced

metalworker and so i have no reason to doubt his words.

if his english was a little better he'd be posting here himself.

joe, thanks, i already called him and told him to do the spark plug test you and greg suggested.

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i just got a call, he pulled the plug wires one after another and the rapping stops when he pulls #4.

thanks a lot for your help, that narrows things down. i'm curious what will be found when the pan is pulled. he plans to pull piston and connecting rod on #4 and have a good look at them.

thanks again!

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  • 3 weeks later...

ok, this took a while but now the culprit was brought to daylight.

here is piston #4:

8607338sox.jpg

8607339wxx.jpg

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8607342toy.jpg

yikes.

that explains why the noise was louder when the engine was still cold...

note the crazy groove in the piston, it continues under the lower ring

over to the other side and allows the piston to flex. i have never seen

anything like that before. looks like the russians made quite some changes

to the mopar layout, the intake/outlet ports, pistons, who knows what else.

wrist pin and connecting rod bearing seem unharmed.

Edited by Cpt.Fred
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there are two deep scratches in the wall, but no material welded on there from the seizure. he says he's going to try honing first and see how it looks like afterwards.

the pistons is not cracked.

i told him to pull #3 as well, just to be sure.

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