Engine knock after rebuild.....need advice Options

[LCOX]

This on going problem started after I rebuilt my 1.8 engine last year. Since then I haven't driven the car and I've put it on the back burner and finally ready to face it again.

Rebuilt the 1.8 with all new bearings and new rings. There is a definite engine knock at idle and throughout the rpm range. This is not a ticking noise like a valve out of adjustment but a bottom end knock.

I did check valve adjustment and everything I could think of. When I pull the #3 spark plug wire the knock almost completely goes away but not completely but definetly better

A couple members said it was probably a rod knock so with the engine in the car I pulled the head and #3 piston and cylinder and tried another rod but the knock is still there.

So I guess take the engine apart and look for a mistake I made on the bottom end rebuild right? Anything else I can try? Thanks in advance. L

[ConeDodger]

Take it apart and mic the crank...

There is no way to fix a bottom end knock without pulling it apart. This is part of the responsibility of doing it yourself. That thing should have been out and apart right away. Staring at it will not fix it. You're the builder. Quit wishing and take it out. I know the paralysis you are feeling. It will not fix itself and asking a question here will not help. There is either something wrong with the rod bearing or the crank. Go find out... (IMG:style_emoticons/default/sad.gif)

Good luck...

[earossi]

Cone Dodger did not mince words with you. Unfortunately, I believe that he is right on. Unfortunately, rebuilding one of these motors is not merely taking it a part and replacing parts with new parts.

You did not mention what dimensional checks were done on the motor, and what machining was required before reassembly.

A rod knock is distinctive and destructive. Hopefully, you have not run the motor long enough to have damaged the crank.

[reharvey]

Cone Dodger did not mince words with you. Unfortunately, I believe that he is right on. Unfortunately, rebuilding one of these motors is not merely taking it a part and replacing parts with new parts.

You did not mention what dimensional checks were done on the motor, and what machining was required before reassembly.

A rod knock is distinctive and destructive. Hopefully, you have not run the motor long enough to have damaged the crank.

(IMG:style_emoticons/default/agree.gif) It's a tuff thing to face but needs to be taken apart. I feel your pain because it has happened to me.

[ConeDodger]

Self loathing I guess...

What we see sometimes is a reflection.

I have done this myself, it didn't work out, you are putting off the inevitable because you 'wish' it would magically work out.

My apologies for the harshness you might perceive. It was meant for me. You/I have wasted a year. Taking it out and apart will only take a weekend.

[Bartlett 914]

My Son and I recently did a Nissan 240 motor. We failed to get oil pressure up in time. We had some difficulty with fuel and a timing issue. Result was a damaged rod bearing. My Son then went out to show is friends is new car. 50 miles later a total melt down. Metal in the oil ruined pistons and damaged calve train. Di is young and didn't stop soon enough to save the motor.

Tear it down. It will not get better

[saigon71]

Did you have the case line-bored during the rebuild?

Years ago a buddy built a 1776CC type 1 engine. The case had to be line bored to true it up. When he fired it up, there was a horrific knocking sound. Upon investigation, he used standard bearings instead of the oversized ones required with a line bore. (IMG:style_emoticons/default/sad.gif)

Good luck with the project and keep us posted as to what you find.

[r_towle]

you can pull and strip a motor in one day.
Then take the crank, rods and case to a machine shop for inspection.

You will need to order a new gasket kit...
you will need to order new rod and main bearings.
I would hold off on any bearing order until you hear back from the machine shop.

Could be two long weekends, fixed.
Might be a few weeks in between for machine work to be completed...

Don't avoid it, just get it done and you will be happier in the long run.
It will also be alot cheaper to do it while you have not wrecked anything.

[76-914]

Did your valve train geometry change (higher lift cam)? If so check your valve covers for dents.

[worn]

This on going problem started after I rebuilt my 1.8 engine last year. Since then I haven't driven the car and I've put it on the back burner and finally ready to face it again.

Rebuilt the 1.8 with all new bearings and new rings. There is a definite engine knock at idle and throughout the rpm range. This is not a ticking noise like a valve out of adjustment but a bottom end knock.

I did check valve adjustment and everything I could think of. When I pull the #3 spark plug wire the knock almost completely goes away but not completely but definetly better

A couple members said it was probably a rod knock so with the engine in the car I pulled the head and #3 piston and cylinder and tried another rod but the knock is still there.

So I guess take the engine apart and look for a mistake I made on the bottom end rebuild right? Anything else I can try? Thanks in advance. L

I think it is interesting that the thing changes when you pull the #3 plug. That means I assume that the others do not affect the knock? That tells you that the compression gasses in #3 deform something that goes clunk in the day. The most obvious is #3 rod at the crank. Replacing the rod was heroic, but if you were not able to mic the crank at the time I think inconclusive since if it was undersized at the journal it would still be with a new rod. Were you able to see anything of interest after you got the piston out?


I can't see how not dropping the engine is going to get you anywhere. Seems like having the case on a stand is going to be easier than crawling over and under.

Two winters ago I did sort of the same thing. I did all my own measuring and even decked the heads myself. It was gamble all the way, doing the math and compression ratios with home-made jigs. No line boring because I couldn't detect a need with feeler gauges and a straight edge. All along I knew it might have to come back out. I hope it is in 50-100k miles though. As one poster pointed out though it could be a lot less. Best of luck.

One think you might use is one of those cheap stethoscopes. I was amazed using it when we lit the engine off - you can hear all the different parts doing their jobs and you can separate them out depending on where you touch the rod to. For anyone who hasn't tried it it, it is pretty wild. Have a go at it and see what you hear - at idle; for a short time.

[veekry9]

"One think you might use is one of those cheap stethoscopes. I was amazed using it when we lit the engine off "

Yup,it works,as shown in the movie Das Boot.
sorta like this..



And for some great reception..



Knock Knock..
Its a drag,but you gotta do it.
Get yer wrenches out and dig in.
(IMG:style_emoticons/default/chowtime.gif)

[larss]

... so with the engine in the car I pulled the head and #3 piston and cylinder and tried another rod....

Off topic but how could you pull the head and switch rod with the engine still installed?

/Lars S

[Dave_Darling]

Removing at least the two front (or two rear) cylinders and pistons. Then you can work around the rod in the opposite half of the case.

A serious pain in the butt, if you ask me.

--DD

[larss]

Removing at least the two front (or two rear) cylinders and pistons. Then you can work around the rod in the opposite half of the case.

A serious pain in the butt, if you ask me.

--DD

Thanks but I dont see how one can get the heads off, the valve covers in my 914 are WERY close to the surrounding bodyparts...I have problems in adjusting the valves and can not dream of lifting the heads over the head bolts...but if someone has done it it must be possible...


/Lars S

[Dave_Darling]

Oops, brain fart. For some reason, I thought you were asking about doing it without splitting the case....

Yeah, the motor comes out--no way around that. Not unless you want to sawzall the body up and then weld it all back together again after. (IMG:style_emoticons/default/wink.gif)

--DD

[stugray]

It's a little easier for me because of carbs instead of FI, but:

Disconnect electrical, Position car on stands, remove rear wheels, drain oil = 45 min.
Remove shift linkage, throttle & clutch cables, & exhaust (at the stub pipes) = 1 hour
disconnect axles @ trans only = 15 min.
Drop engine partway = 30 minutes
Disconnect trans ground strap that you forgot = 2 minutes
Finish engine drop & pull out rear = 5 minutes.

Split engine from trans & remove clutch = 15 minutes
install yoke & Lift onto engine stand (5 minutes & 1 hour finding someone to help lift it)
Disassemble - depends on how cautious you are....

[larss]

Possibly "with the engine in the car" means the engine sitting in the rear boot... then its possible to lift the heads (IMG:style_emoticons/default/biggrin.gif)


/Lars S

[worn]

Oops, brain fart. For some reason, I thought you were asking about doing it without splitting the case....

Yeah, the motor comes out--no way around that. Not unless you want to sawzall the body up and then weld it all back together again after. (IMG:style_emoticons/default/wink.gif)

--DD

Are you sure? Wouldn't want to try, but without the exhaust and valves you get more wiggle, and maybe the axles aren't in either.

[Dave_Darling]

The heads will hit the suspension console long before they slide off the longer studs.

You can probably slide them off if you disconnect the engine and lower it ~6", but by that point you're only a couple of wires and cables from completely removing the engine from the car anyway. And it's a heck of a lot easier to deal with it on the bench than hanging halfway out of the engine bay.

--DD