I accept that it is virtually impossible to diagnose the cause of a knock, tap or squeak without actually hearing it first hand, but I wonder if in this case someone could either confirm or question my suspicions on the origin of a knock that is emanating from my 30BHP engine

My suspicion is that it is a small end knock based on the following:

It is only audible during idle, and even then it comes and goes.

It is a low down knock.

It disappears as soon as the engine revs are increased.

It can’t be heard when the engine is under load.

My feeling is that anything from the big end side of things would be there at all engine revs and would be particularly noticeable when the engine is under load. :?

What thoughts have you?

Thanks

Mike 😎

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George Lloyd might be able to confirm what a small-end knocking noise sounds like as I think he had that problem with his Karmann...


:d

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Is this a dual carb setup? An imbalance (or even a fault/blockage etc.) between carbs can sometimes cause 'clunking'.

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No, it's just a standard 30 horse engine - single carb. I built it up in a rush in order to get the car MOTd and on the road in time for Stanford Hall. But in hindsight I think I should have spent more time selecting the gudgeon pins that were best suited to the small end bearings in terms of wear, as it was I used the gudgeon pins from the piston set thinking it best to keep them matched.

Mike

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Difficult as you say without hearing it.
But it does describe as a small end bearing.

When i had the problem... it sounds like a rapid metallic tapping(and yes it sounds like only when the engine is not under load but listen carefully it is there).I had always heard the 25/30 hp engines very seldom suffer from this problem but apparently it is quite common.
I suffered just 400 miles after paying a reputable professional for a full on rebuild.

Folks if you have the cash and want a good job,go to John Maher.....CRY ONCE.

A quick up date, once again in anticipation of Stanford Hall I had the engine out of the oval, primarily to replace the crankshaft oil seal. Whilst the engine was on the bench though I popped the heads and barrels off and took a look at the small ends.

The gudgeon pins I had built the engine up with had noticable wear so I hunted around and found a set of four that seemed better. I reassembled the engine using them and to my great delight the top end rattle has gone! :d

The engine sounds very sweet now, despite the fact that I cobbled it together out of spare parts.

So, off for its MOT this week and all being well the rear wings are being tidied up next week and then it should be all set for the Historic Line Up at Stanford Hall 😎 .

Mike

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See you there .I got mine mot'd last week just for the occasion.Is this your car?



Or this one

Mine is the second one, 409 UXD (originally 8023F). It doesn’t look a lot different to your photo from 2009 but hopefully, by this years event, the rear wings at least will be tidied up. Since last year though, I have met the son of the original owner and have put together a lot of anecdotal history for the car from new in 1957 through to 2003 when it was sold for the first time.

I have also bought a couple of nice period correct front wings from that nice Mr Oakley which will hopefully be getting renovated and fitted later in the summer. :wink:

As the car is still largely in original paint, I am trying to hard not to do any more to it than is necessary to both preserve it and make it look reasonably smart.

See you there!

Mike

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Certainly looks better than mine !Thats great you have the history.I bought some wings for mine 3 years ago and still havnt done anything with them :oops:

Update: MOT passed, the only advisory was the headlights. The tester said "I'll let it go because I can't imagine you would drive this car at night with lights like that". As it happens, I have, and it was a very scary experience navigating the windy roads over the downs in pitch darkness after leaving a country pub. My partner couldn't believe the lights were on!

Anyway, MOT passed, engine purring like a kitten and the car has been dropped off at the body shop for the rear wings to be tidied up. All being well should be in the Historic Line Up at Stanford Hall next weekend.

See you there. :wink:

Mike

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