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Engine Knock


David McHugh
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Hi Chaps, can anyone help me out with a engine knock?

I was driving along in my MKIV Spitfire 1300 at about 65 mph when there was out of the blue a horrible knocking sound. I immediately slowed down and stopped, the breakdown guy had less idea than I did, however while he was there I got him to take off the rocker cover to see it there was anything obvious, which the  was not. After getting the car home a neighbor said that he thought it sounded like the timing. Before i set out on my trip, i installed a electronic ignition and when doing so I had to force the black cylindrical ring that goes on the center shaft right below the rotor arm, this was because of a off white plastic post with a slightly larger diameter head (this was supposed to have been removed when i did the install)  that was attached to the plate and was in the way. This post would have stopped the automatic timing adjustment made by the vacuum. Anyway I removed it, bought a strobe light and reset the timing and set up the carbs. There is definitely an improvement but at high revs it still occasionally knocks. There does not seem to be any kind of rhythm in the knock it is random, it almost sounds like something is loose and occasionally gets thrown around.

My plan is to start a process of elimination even with the water pump and timing chain, although unlikely it won't hurt to change them and at the same time i can be confident that it is not them. I was then thinking of taking the sump off and checking the bigends.

Your thoughts, ideas etc will be greatly appreciated.

David.... 

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I had an Accuspark kit on a Delco 4 dizzy which i think is what you should have on that engine.The rotor arm didn`t sit high enough on the spindle and hit the electronic ignition module every time it went round until it died.

 

I had to replace it and modify it.

Is yours a mechanical engine knock or plasticky?

Steve

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Big ends would be rhythmic and worst under load. I'm guessing from what you've said it does it when stationary?  I'd try putting the points and condenser back, when I do stuff it's generally the last thing I did that screwed it up! 

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Could be timing. The original timing figures are no longer valid. Different grade of fuel, worn components etc so you may need to retard the ignition slightly.

 

If it is timing, it should be worse under load. ie going up an incline, lower revs/high gear. Also try disconnecting the vacuum advance.

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Get the old wooden handled screwdriver and use it as a stethoscope

makemthe blade contact the engine and holdnear on the handle

dont get it in the fan or it will need surgical removal !!!!

 

You will soon home in on the location of the knock

 

I is it at engine speed or camshaft speed ??

 

You say its random which could be cam follower etc.

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Thank you for your responses, here are the answers to the respective questions you have asked.

 

It is defiantly a mechanical knock not plastic.

Yes it does it when stationary but not on tick over, I will try putting the points and condenser back in tomorrow providing i can find the plastic post as i can't

think what i did with it, woops.

When it started i was on the flat and as yet have not driven on a hill to know if it is worse under load. I have the timing set at 8 degrees BTDC as in the Haynes. The vacuum did not seem to make any difference. 

I have bought a mechanics stethoscope which will be here tomorrow, i don't have a wooden screw driver or any other suitable wooden handled tool.

I will update you tomorrow, thanks again

David... 

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I have not been able to find the part out of the distributor so not been able to put points back, will keep looking or source the part.

I tried to use the stethoscope to locate the knock but with not much luck for several reasons I will try again tomorrow.

My neighbor commented that it sounds  like a nut banging around in a washing machine. The knock is defiantly from within the engine somewhere.

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Thank you for your comments Pete.

The starter is okay, that was one of the first things i checked. When I was having a listen with the stethoscope the sounds seemed to be the same regardless of where i was listening, having said that, i gave up with the stethoscope as it was quite windy today and the stethoscope has a long metal probe which would be better if it was covered which would also help to pinpoint a particular sound, the other thing, is that things never happen when you want them too, I hope i have better luck tomorrow.

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