Engine Knocking after rebuild Options

[LCOX]

I've got a sick feeling I'm going to have to take my 1.8 engine out and completely apart again after rebuilding it.

Cranked it up for the first time after rebuilding it(all new bearings, new rings, head work and gasket set).

The engine has a knock fairly loud at idle but when the engine rpm's are around 1500 it starts to quieten down and at 2000 rpms the knock goes away completely only to come back at idle when rpms are around 800-900. Other than that the engine appears to run very smooth.

Where to I start here. L

[bulitt]

Pull the coil to distributor wire. Then crank it. Do you still hear the knocking even tho it's not firing?

[sean_v8_914]

what pistons did you use? might be skirt slap. does it go away when engine is warm to FULL operating temp?

[aircooledtechguy]

Before assuming the worst, take a methodical look at it and go over the basics.

-Valve adjusters; you may have had one or more come loose. I see this often on customer cars.
- Exhaust gaskets; an exhaust leak at the head can have a metallic sound and make you think the motor needs to come apart.
- Hand crank the engine at TDC and rock it back and forth with the plugs out. If you truly have a rod knock, you'll likely be able to make it knock and hear an audible "clunk".

Never assume anything. . . Good Luck!!

[mrbubblehead]

you could pull the spark plug wires one at a time while the engine is running. to see if the knock disappears.you can isolate that way.

[LCOX]

Update: I followed Mr Bubbleheads advice and pulled one spark plug wire at a time with the engine running.

The knock went away when I pulled #3 wire. So I guess the next thing to do is to check valve adjustment on #3 right?

Bulitt. Couldn't hear it knock when I cranked it with the coil wire disconnected.

Sean. I reused the factory German KolbenScmidt pistons.

Aircooledtechnology. I rocked the car back and forth with the plugs out at TDC on each cylinder and couldn't hear or fill a knock.

[Bartlett 914]

what pistons did you use? might be skirt slap. does it go away when engine is warm to FULL operating temp?

With this in mind, did you put the pistons in facing the correct direction?

[VaccaRabite]

Are there spacers under the valve rockers?

If so it common for the rockers to tap against the inside of the valve covers. Since you are going to check valves anyway, give the covers a look and make sure there is no indication of impact. If there is just clearance the rocker screw a little.

Zach

[mrbubblehead]

Update: I followed Mr Bubbleheads advice and pulled one spark plug wire at a time with the engine running.

The knock went away when I pulled #3 wire. So I guess the next thing to do is to check valve adjustment on #3 right?

Bulitt. Couldn't hear it knock when I cranked it with the coil wire disconnected.

Sean. I reused the factory German KolbenScmidt pistons.

Aircooledtechnology. I rocked the car back and forth with the plugs out at TDC on each cylinder and couldn't hear or fill a knock.

i was hoping you WOULDNT hear a change. unfortunately its almost certainly a rod. of course check the valve train. but the valve would continue to make the sound weather the plug was firing or not. but since u pulled the plug and took the pressure off that cylinder and the knock stopped, i think your gonna have to tear it down again. at least you know where to focus your attention now.

[larss]

and couldn't hear or fill a knock.

i was hoping you WOULDNT hear a change. unfortunately its almost certainly a rod. of course check the valve train. but the valve would continue to make the sound weather the plug was firing or not. but since u pulled the plug and took the pressure off that cylinder and the knock stopped, i think your gonna have to tear it down again. at least you know where to focus your attention now.

I have exactely the same symptoms on my newly rebuilt std 1,7 (all new bearings, new rings, head work and gasket set). Have been running about 2000 miles since the rebuild and it hasn't got any worse.

If it is the rod would it likely be at the small end or..?


/Lars S

[malcolm2]

So what is it about a rod that will make the knock?

Big end bearing on the crank or little end bushing wobble on the pin, maybe wrist pin movement? As some of you may know, I am starting to RE-assemble my engine for the 2nd time and if there is something I can check while the case is split, I WANT TO CHECK IT.

[stugray]

I WANT TO CHECK IT.

The large rod ends are just about the only simple place on these engines you can check with plaistgauge.

When I reassembled my engine this last time, I used some rods from the PO and some brand new KB pistons & wrist pins.

I sent in the rods to be rebushed and checked.
The shop complained that I did not send them any wrist pins.
I thought why the hell would they need the wrist pins, arent they all just one size?

Well the shop told me that the rods did not need to be rebushed as they had just been done, BUT they guy said the engine would have probably siezed almost immediately because the wrist pin bushings had not been properly sized after being replaced.

He also straightened one rod for me.

SO.... make sure the wrist pins are not binding in the rod bushing too.

Stu

[sean_v8_914]

aircooledtechguy said something very important:
always check the simple stuff before assuming anything. this is good advice worth mentioning again.

[LCOX]

If it is a rod can't I take it off the crank without splitting the case after removing the head and both pistons and cylinders?

[LCOX]

I just checked the valve adjustment on #3 and it's spot on. No problems appear to be here.

Mark. From what I remember the arrow on each piston top is pointing towards the flywheel.

Zach. No spacers were used under any of the rocker arm assemblies.

[worn]

If it is a rod can't I take it off the crank without splitting the case after removing the head and both pistons and cylinders?

No, you can remove a rod without splitting the case. You do have to pull the engine though and remove the cylinder. My question though would be under the circumstances what else is wrong? If you find one smoking gun, maybe just the rod work would be OK, but it may be something really bad in one spot and sort of bad in the rest. That would be my luck.

As it happens I am pretty sure that I made a compression ratio error on my 2.0 build just completed. Pinks/pings under load with 93 octane. So as Joe Walsh put it: welcome to the club
http://youtu.be/OA6Qa3z0igM

But you can be sure I am looking for other causes of the sound...

[TheCabinetmaker]

Worn, please splain the "no, you can" thing to me. Just don't want to assume something.

[Dave_Darling]

You can pull the cylinders off, then the pistons, and work around the rods to reach in and remove the conrod bolts. You reach in through the spigots where the pistons go.

It doesn't look like much fun, but it's probably less work than tearing the entire thing down. But you won't get to check as many things.

--DD

[stugray]

Whenever I need to pull the cylinders, I pull them with the pistons still inside. It saves wear & tear on the rings.
Slide the cylinder out over the piston until the wrist pin is exposed, then pull the pin.
You have to install/remove them in a certain order to have enough room.

Yes you can remove the rods without splitting the case.
But you pretty much need to have the opposing cylinder off too. SO you pretty much need to pull them all.

Worn,

Pinks/pings under load

What was your deck height?

Stu

[worn]

You can pull the cylinders off, then the pistons, and work around the rods to reach in and remove the conrod bolts. You reach in through the spigots where the pistons go.

It doesn't look like much fun, but it's probably less work than tearing the entire thing down. But you won't get to check as many things.

--DD

Exactly what I meant to say. Thanks Dave.