Motor rod knock how to correct?

[mll1446]

I have a knock in my motor can the piston be taken out of the engine through the bottom of the motor and replaced if so how ? Thanks

[Tom Wesenberg]

No.

[mll1446]

Cam rod be replaced without removing piston

[roccaas]

Not worth it. You need to make the wrist pin to piston fit so precise that it would be a real feat to do it with the skirt of the piston hanging just below the bottom edge of the block, and just above the crankshaft. I'm not even sure you could get the skirt of the piston low enough to remove the wrist pin and reinstall with a new rod and wrist pin.

Question: you mention motor knock. Do you know it is the piston, and not the big end of the connecting rod? If it is the big end (which happens quite often in 82 year old motors), you can reshim the big end from the bottom and not worry about the piston. It's an oily messy job, but satisfying when completed correctly.

[mll1446]

I have to investigate I know that something's not right and there is a knock

[James Rogers]

Sponsored Links (Register now to hide all advertisements)

Originally Posted by roccaas

Not worth it. You need to make the wrist pin to piston fit so precise that it would be a real feat to do it with the skirt of the piston hanging just below the bottom edge of the block, and just above the crankshaft. I'm not even sure you could get the skirt of the piston low enough to remove the wrist pin and reinstall with a new rod and wrist pin.

Question: you mention motor knock. Do you know it is the piston, and not the big end of the connecting rod? If it is the big end (which happens quite often in 82 year old motors), you can reshim the big end from the bottom and not worry about the piston. It's an oily messy job, but satisfying when completed correctly.

You are right,not worth it but, As for pulling the piston down far enough to remove the rod, it can be done but, takes finesse'. Fitting the wrist pin would be no more a problem doing this than it would be with the piston out of the motor. Simply remove the pin from the piston and leave the piston hanging in place. The wrist pin and rod can then be fitted and replaced, the piston pushed back up and the rod reconnected to the crank and fitted. The biggest hazard to doing this would be if the piston is pulled down too far and the bottom ring pops out, you got a baaaaad problem. I have done this in Model T's and A's and one Jeep. Never had but one ring to pop out. I learned a valuable lesson on that one, it is not worth the time or possible trouble.

[roccaas]

James, can you bring the piston down far enough with the crankshaft in place? Even with it "cranked" away from the bottom of the block?

The one time I took up the shims, the crank/block interface seemed to be a cramped place.

[roccaas]

Originally Posted by mll1446

I have to investigate I know that something's not right and there is a knock

Having run into this often, some tips.

Run the engine. If it knocks when the spark is advanced (left lever down), suspect the big end. If you can accelerate with the spark fully retarded (left lever UP) and no knocking -- Big end is loose.

Short our each plug individually to see if the knock goes away on the "dead" cylinder.

Pull the pan, give the engine a day to finish dripping. Buy one of those full face mask shields. Give each rod a twist by hand. The knocker will probably feel significantly looser than the non-knockers.

Les Andrew's book gives a great set of instructions for diagnosis including descriptions of the sounds (bell-like, clank, rattle, etc).

[James Rogers]

Originally Posted by roccaas

James, can you bring the piston down far enough with the crankshaft in place? Even with it "cranked" away from the bottom of the block?

The one time I took up the shims, the crank/block interface seemed to be a cramped place.

Very tight! That is one reason why it is not worth the time or trouble but, it can be done. I did it the other times because I didn't have the proper tools to remove the engine and do the work or a lift to pull the motor. Poor boys got poor ways.

[columbiA]

Ive never had a problem adjusting the rods or mains in the car.I find it easier to do the job in the car rather than removing the engine If engine is out of car for rebuild etc,then its easier to do on the stand.Often on a well used engine,the wrist pins will be worn.I usually replace them with .002" or .003" OS pins & hone to fit.

[mll1446]

Changed head gasket had head filed down . Was coolant in piston area. Still engine knock

[Tom Wesenberg]

Is this a metalic knock? Or an ignition knock?
Does it make the noise at all speeds? And temps?

Did you clean any junk out of the water chanbers while the head was off? My engine had an accumulation of rust and junk near the rear of the block, and the engine would knock with the slightest acceleration. Once I cleaned the junk out the knock went away. Hot spots can cause an engine knock.

[Charlie Stephens]

Originally Posted by mll1446

Changed head gasket had head filed down . Was coolant in piston area. Still engine knock

I assume "head filed down" means it was milled, was this when the knock first appeared? You may have a piston hitting the head if you didn't check it, or maybe an undersized gasket contacting the piston.

Charlie Stephens

[mll1446]

Makes noise at all speeds, when spark lever is down its louder. Did clean out junk , noise is immediate when started