Main rod bearing? (1 Viewer)

[Rochfort]

Knocking at high RPMs. Main rod bearing? Comes from bottom rear of engine, I make it just above the crank.

 

[1911]

Knocking at high RPMs. Main rod bearing? Comes from bottom rear of engine, I make it just above the crank.

What is your current ignition timing? Oil pressure? How many miles on this bottom end?

Any reason to suspect carbon build-up in the head?

These F-series lower ends are robust; just looking for other possibilities before you have to rebuild the bottom end.

 

[Rochfort]

What is your current ignition timing? Oil pressure? How many miles on this bottom end?

Any reason to suspect carbon build-up in the head?

These F-series lower ends are robust; just looking for other possibilities before you have to rebuild the bottom end.

Thanks! Good questions. Oil pressure drops with low RPMs. Otherwise healthy with normal idle. Just redid the valves, rings, pistons. Not sure what else, my mechanic died abruptly. Adjusted the timing two days ago. Bottom end no idea. Probly original. It's a 1978.

 

[peesalot]

Does the crank go forward and back with throttle ?

 

[pjohnson]

With it warm and idling, pull each plug wire to determine which cylinder is the problem. Could be a wrist pin.

 

[Subterranean Nik]

Agree with above checks. As the fine owner of a spun rod bearing 2F from a month ago, hope you are luckier than me.

With that said, mine started with a “high RPM knock” took as another issue as pressure, etc… on a fresh motor we’re all great.

A bit more evasive, but once ruled all the external checks out… dropping the pan and checking from underneath pretty quick task. Mine was obvious, metal flakes in the pan and when looking up…all bearings had oil on the caps but one. She was bone dry, popped the cap and there was the spun bearing.

Good luck, keep us posted.

Nik

 

[Rochfort]

Agree with above checks. As the fine owner of a spun rod bearing 2F from a month ago, hope you are luckier than me.

With that said, mine started with a “high RPM knock” took as another issue as pressure, etc… on a fresh motor we’re all great.

A bit more evasive, but once ruled all the external checks out… dropping the pan and checking from underneath pretty quick task. Mine was obvious, metal flakes in the pan and when looking up…all bearings had oil on the caps but one. She was bone dry, popped the cap and there was the spun bearing.

Good luck, keep us posted.

Nik

Excellent! Thanks.
Actually it

Does the crank go forward and back with throttle ?

.
Actually I adjusted the throttle linkage and now it idles/accellerates fine. Needed a new bolt. Not missing or fogging. Good smooth accelleration. There is a faint intermittent knock but I think it's from the top end. Like one end of the camshaft Is slightly unaligned and rattling around. My mechanic may have screwed up somewhere...he passed away shortly after doing the top end. "Either this cruiser goes over I do!"
.

 

[Rochfort]

With it warm and idling, pull each plug wire to determine which cylinder is the problem. Could be a wrist pin.

Thnx will do.
.

 

[Rochfort]

With it warm and idling, pull each plug wire to determine which cylinder is the problem. Could be a wrist pin.

.
Right. No load, no noise.
.

 

[peesalot]

Search on here for top end oiling issues, if you have had the cover off and verified oil in rocker assembly then nevermind but there is a bit of knowledge regarding that oil passage and it can easily get wrong thereby depriving rockers of proper oil flow. Did you ever see if crank is faintly moving fore & aft with throttle, like if its idling and you goode it ?

 

[Rochfort]

Search on here for top end oiling issues, if you have had the cover off and verified oil in rocker assembly then nevermind but there is a bit of knowledge regarding that oil passage and it can easily get wrong thereby depriving rockers of proper oil flow. Did you ever see if crank is faintly moving fore & aft with throttle, like if its idling and you goode it ?

.
Had the cover off, did valve alignment. Looked oily to me. Not sure how to observe the crank moving fore and aft?
.

 

[peesalot]

Just look at the pulley while reving it, come on and off the throttle, if its moving you'll see it , even a smalll amount indicates thrust surface wear inside.

 

[Rochfort]

Just look at the pulley while reving it, come on and off the throttle, if its moving you'll see it , even a smalll amount indicates thrust surface wear inside.

.
Fore and aft?
OK I get it...

 

[Rochfort]

Just look at the pulley while reving it, come on and off the throttle, if its moving you'll see it , even a smalll amount indicates thrust surface wear inside.

Pee, while I've got you...what do you think of lifting the cabin and bolting it down on a half inch of rubber. To get a quieter ride...

 

[peesalot]

IMO I would use stock mounts. Lots of work to source your own spacer/insulator material and if its soft enought o really quiet things it will blow out. I offer the main effort could be toward motor mounts and mid mounts as when that rubber gets hard it is useless. Also in effort to quiet things proper spring/shackle bushings do wonders. If its not off road serious you can use the stock oem rubber vs the aftermarket poly bush for motor/mid & springs/shackles as they are softer. Properly greased spring/shackle bushings will also help alot.

 

[Rochfort]

IMO I would use stock mounts. Lots of work to source your own spacer/insulator material and if its soft enought o really quiet things it will blow out. I offer the main effort could be toward motor mounts and mid mounts as when that rubber gets hard it is useless. Also in effort to quiet things proper spring/shackle bushings do wonders. If its not off road serious you can use the stock oem rubber vs the aftermarket poly bush for motor/mid & springs/shackles as they are softer. Properly greased spring/shackle bushings will also help alot.

Great!!

 

[Rochfort]

IMO I would use stock mounts. Lots of work to source your own spacer/insulator material and if its soft enought o really quiet things it will blow out. I offer the main effort could be toward motor mounts and mid mounts as when that rubber gets hard it is useless. Also in effort to quiet things proper spring/shackle bushings do wonders. If its not off road serious you can use the stock oem rubber vs the aftermarket poly bush for motor/mid & springs/shackles as they are softer. Properly greased spring/shackle bushings will also help alot.

.
Great. Got motor mounts when we did the engine. Leaf bushings Great idea! No coils on this puppy...

 

[pjohnson]

Pee

I think you have a new nickname John @peesalot

 

[Rochfort]

Agree with above checks. As the fine owner of a spun rod bearing 2F from a month ago, hope you are luckier than me.

With that said, mine started with a “high RPM knock” took as another issue as pressure, etc… on a fresh motor we’re all great.

A bit more evasive, but once ruled all the external checks out… dropping the pan and checking from underneath pretty quick task. Mine was obvious, metal flakes in the pan and when looking up…all bearings had oil on the caps but one. She was bone dry, popped the cap and there was the spun bearing.

Good luck, keep us posted.

Nik

.
Dammit
Was the crank scored up? Have to pull it?
.

I think you have a new nickname John @peesalot

.
Can't believe the drive train on this thing. Tight shifts, no slippage, no clanking U-joints. And It's older than I am. Tough!

 

[peesalot]

It's Mellonhead, ask wngrog.