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Beetle Severe Engine Knock
paslow22 - January 2nd, 2018 at 05:08 AM

Hello, and H.N.Y.

My latest problem is a severe engine knock that started as if someone turned on a switch.
I have twin 40mm carbs and found adjusting them was difficult so I purchased an off set manifold kit, swapped them over and all was fine with the engine running as normal and increased engine speed numerous times with no problems.

Decided to do a road test and went approximately 1 klm then all of a sudden a very severe engine knock with no warning.

I was extremely careful about dropping something down the manifold throats but there may have been something there previously just waiting for it to drop into the heads when I pulled of the previous manifolds.

My theory is something has fallen into the motor and then sucked into the bore and is probably been wedged into the head. ( bugger)

Would a washer be able to pass by the valves.

Also I decided to check valve clearance and found 1 and 2 rockers to have excessive gap between them and solid spacers, but I don't think this would cause instant knock.

This is a Scat import motor (not by me) and all the spacers are the same size.
width.

So my thinking is to pull out the motor and pull the heads off and check the bores and if nothing found pull the case apart and rebuild.
This motor has only 5000 klms.
I am not a mechanic but I just like pretending I'm one and I like to learn things or try to work it out.

Thanks for all your help.

Darryl

Bizarre - January 2nd, 2018 at 07:01 AM

Yes. A washer can get past valves.

Does it sound if it is coming from within the block or the heads?

If it is a washer you may have chewed up the piston and valves.
These could need replacing.

If not a washer and noise is coming from block then maybe bearing?

paslow22 - January 2nd, 2018 at 12:12 PM

Quote:
Originally posted by Bizarre
Yes. A washer can get past valves.

Does it sound if it is coming from within the block or the heads?

If it is a washer you may have chewed up the piston and valves.
These could need replacing.

If not a washer and noise is coming from block then maybe bearing?


Thanks,
I tried the screwdriver test to the block and it just didn't seem to be coming from there so it most probably be the pistons and bore.

I haven't tried to test the heads yet, but if it is I am so not looking forward to pulling it out again, I pulled it out to clean out the bore and piston early last year due to a fire the previous owner had.

Thanks again
Darryl

MR930 - January 2nd, 2018 at 06:50 PM

My son dropped a washer working on his car, it got stuck in the valve and was touching the piston. Motor out and heads off unfortunately.

paslow22 - January 2nd, 2018 at 09:05 PM

Quote:
Originally posted by MR930
My son dropped a washer working on his car, it got stuck in the valve and was touching the piston. Motor out and heads off unfortunately.


Thanks, I didn't want to hear that, but it was in my thoughts all along and I was just fighting the inevitable,

Darryl

grumble - January 3rd, 2018 at 08:54 PM

It is possibly a tinware screw that had worked out and slipped into the inlet and is either wedged into the top of the piston or stuck in the manifold holding the valve open. Do a compression leak test and then dismantle.

paslow22 - February 1st, 2018 at 08:43 AM

Quote:
Originally posted by grumble
It is possibly a tinware screw that had worked out and slipped into the inlet and is either wedged into the top of the piston or stuck in the manifold holding the valve open. Do a compression leak test and then dismantle.


Latest update,

I pulled out the motor and found a small stainless washer embedded into the head, and slight indents in the piston with no damage to the bore, the head was machined and compression increased and I decided to fit 1.25 rockers.

When I went to shorten the push rods in the lathe the ball end just fell off the end of the chrome moly rods with nothing inserted into the tube.
So new super duty alloy rods and wide mouth tubes this time thanks Rod, the original pushrods were in the motor, Scat x USA import by previous owner.
Push rods will be shortened today and then I can get busy and complete the motor and install.

Darryl

beetleboyjeff - February 1st, 2018 at 08:52 AM

Good news about the lack of major damage. It sounds like you may have dodged some bullets with the push rods & tubes too.