Knocking/tapping in 918 side valve

for those with Series MM sidevalve cars produced between September 1948 and February 1953
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karlcouchMM1952
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Knocking/tapping in 918 side valve

Post by karlcouchMM1952 »

Hi, I wonder if someone can help me please. I have recently changed the head gasket on my 918 side valve as it was leaking water quite badly. The new gasket was still leaking water so I had the head very lightly skimmed and used some blue non drying compound it stick it down with new head gasket which has done the trick and has stopped the water leak. However, I now have a new problem which is a loud tapping/ knocking noise coming from what sounds the top part of the engine? Is this something I may have caused? The car starts first time and appears to run well with no back firing and missing etc, but the noise persists and seems to get louder for a short while then stays about the same. I've tried warming the engine up as I thought it could be a tappet but it doesn't get any quieter. I've checked the tappers and they all appear to be tighter than recommended so should be making a noise. I am really stuck and would really appreciate any help or suggestions. Many thanks Karl.

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mike.perry
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Re: Knocking/tapping in 918 side valve

Post by mike.perry »

Provided that the faces of the head and block are true you should not need any gasket glue (Hylomare?). What make of head gasket are you using? There are some rubbish gaskets around, a good gasket should be hemmed around the outside and drop straight over the head studs, some are just hemmed around the chambers and need pushing down the studs with a box spanner.
I am actually using a second hand gasket at the moment with no problems. Head gaskets should be torqued down to 44 lbs ft. Tappets should be 0.018 cold. Are the cam followers rotating when the engine is running?
Is the noise comming from the distributor or drive?
I assume that it is not loud enough to be bearings.
I had a loud tapping noise which turned out to be an incorrectly fitted baffle plate but unless you have had the sump off this is unlikely to be the problem.
How is the oil pressure? What is it after a brisk run down the motorway and stopping at the end of the slip road?
Just a few unconnected thoughts
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TvdWerf
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Re: Knocking/tapping in 918 side valve

Post by TvdWerf »

I had a little rust on the top, but when placing new pistons, they took a little from the top to get it away.[frame]Image[/frame]
after revision, when the surface is clean like mine, the standard gasket should be ok.[frame]Image[/frame]
Before revision, the rust was to deep to keep all the water inside ;)
MM '51 LHD sidevalve
karlcouchMM1952
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Re: Knocking/tapping in 918 side valve

Post by karlcouchMM1952 »

The head has been skimmed very slightly but I'm not in a position to get the block skimmed currently. That's why I used the sealant and bolted it down at 44lb. The water leak is now sorted to I'm happy with that aspect.

All the tappets are less than 0.018, I haven't run the engine with the tappet cover off to be honest.

I've checked the distributor and the drive looks ok as far as I can see?

It doesn't sound like bearings it's more of a cam tappet tapping sound.

Oil presure is normal about 60 ish when cold. I've not taken further than the street as I'm scared of causing more damage or braking down.

Any ideas would be great. Thanks.

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tortron
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Re: Knocking/tapping in 918 side valve

Post by tortron »

Hi

you may want to try a long screwdriver up to.the engine and the other end to.your ear to help.locate the sound

a few guesses could be something fallen into a cylinder - perhaps the tip off a spark plug
valve bounce hitting the head
piston slap
loose distributor body (the actual body of mine came loose where it mounts to.the head. No shaft wobble at all but the body moved around)
Kind of hard to guess without knowing the area its really coming from.though.

I had an odd suspension knock when i took left hand corners. Turned out to be the horn rotating on its mount and hitting the body
mike.perry
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Re: Knocking/tapping in 918 side valve

Post by mike.perry »

Most things dropping into the cylinder will be ejected out of the exhaust valve. I had a valve seat break up and that just tinkled for a couple of seconds before continuing on three cylinders. It peppered the top of the piston
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karlcouchMM1952
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Re: Knocking/tapping in 918 side valve

Post by karlcouchMM1952 »

I've taken the car out for a run today as I'd reached a do or die situation. It run really well, no lack of power or engine missing etc. the tapping noise was very loud to start but did get quiter when it warmed up and the oil pressure drops to 20 at idle. It however didn't go away. I'm still no wiser on what the issue could be? Any suggestions would be very much appreciated. :)

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smithskids
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Re: Knocking/tapping in 918 side valve

Post by smithskids »

May be a bit of slack in the top end pins? either in the piston or the piston clamp pin slack :o
tortron
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Re: Knocking/tapping in 918 side valve

Post by tortron »

Perhaps an exhaust leak

its not tge fuel pump ticking? ;)
karlcouchMM1952
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Re: Knocking/tapping in 918 side valve

Post by karlcouchMM1952 »

What are the top end pins? Or the piston clamp ring? And how would I check these?

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colin addison
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Re: Knocking/tapping in 918 side valve

Post by colin addison »

Took the MM out for a "Breakfast meeting" this morning and it started making a rattling noise. Made me very nervous. Anyway it was a loose fanbelt!!
smithskids
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Re: Knocking/tapping in 918 side valve

Post by smithskids »

Top end pins or gudgeon pins are the pins that join the piston to the conn rods. On the sidevalve engines they are clamped in the conn rod eye with a small setscrew and spring washer.Can be checked withe the sump off and a long 1/4 inch socket set.But be carefull not to over tighten. :o
karlcouchMM1952
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Re: Knocking/tapping in 918 side valve

Post by karlcouchMM1952 »

The noise seems to be coming from higher in the engine than though to be honest.

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karlcouchMM1952
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Re: Knocking/tapping in 918 side valve

Post by karlcouchMM1952 »

I took the car to show on the weekend. Some of the other owners suggested that it could be the distributor. It does appear to be making a noise and when you touch the distributor it changes the note of the engine, so there must be a lot of wear in the shaft or something. Bad news is, I've spoken to the distributor doctor and its £185 plus vat... Not good. If anyone has a spare distributor that's is in good condition that would be a great.

The car wasn't running that well... It wasn't to bad while accelerating on while on the power. The tapping noise seemed more apparent when decelerating or on overspeed.

So any other suggestions welcomed.

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