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Tapping noise when engine warm


Perfect 65

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Hello everybody, my first post here for a while. I have a good Spitfire 1500 engine which starts and runs fine. Probably needs an expert tune on the carbs but it runs qietly and reasonably smooth. I am planning to put an electronic distributor on it soon. Ive seen some advertised on ebay. Anyway, as the engine warms up and only at a very slow tickover, it starts a-tapping. Not too alarming but irritating but it is quiet when cold. If you give it just a whiff of gas it goes quiet and spins up nicely. The tapping sounds to be synchronised with engine revs as you might expect. The engine was converted to unleaded and a general overhaul some years ago but has not done many miles - been standing for about 11 years I was told by the guy I bought it from recently. I just wondered if anyone has an idea of what would cause this noise. My hunch is it is some end float somewhere, maybe camshaft of distributor shaft. Happy Christmas, Dave

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more than likely the tappets/rockers need setting.
if set to standard, then its 10 thou
BUTT, has it got a modded cam,!! if so, its a guess,as all are diff,and all are bigger than standard,some by twice as much.
may also be  that the rockers are worn, with an indent under the pad,
slacken off, and turn rocker onits back,and loook / feel for indents/wear.

if any wear, then set to lower settings, may need diff settings for diff rockers,if indents are bigger on some than others, follow,!!!

you may find that you will be setting them at any thing between 4 to 6 thou,
dont be alarmed at this, as its only taking the wear up, that the feeler gauge wont let you see.
ohh, above is for standard cam, but same applies for modded cam, just figures will be bigger.
so 4-6 on 10 thou, will be 8 - 12 on a 20 thou uprated cam,

need to measure the indents fust,.
good luck
Marcus

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Thankyou for your comment. Thats interesting because I re-checked the tappets when the engine was warm and the clearance had grown from the original 10 thou as set by me to 12 thou cosistently across all valves. I expected the clearance to diminish if anything. Do you think that 2 thou extra clearance would make such a difference to tappet noise? I will have a look at the rocker pads though as I like to get to know an engine where necessary. I tried listening with the vacuum cleaner rigid pipe to my ear and I thought I could hear more mechanical noise around the distributor adaptor but it was not conclusive. I ran the engine briefly without the rocker cover but the noise seemed to be much the same.

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Yes, especially if the rockers are worn.

even on a good  rockers, I would set mine to a  8 thou, as I did,
reasoning, you got alott of play in the rocker bushes,the bearings
oil film gets thinner as it gets hot, so where ever there is oil, the gaps will get bigger
as oil gets hotter,  least this what Ive found on T engines owa the years.

Even on a tight rocker, the racket that came oot the rockers was alott.
changed to some roller rockers, and its so quiet now.

can get a noise of the points open closing, but not much,

when I set the rockers, I try and turn the engine over a few times first, as Ive found ,as you have said, that the gap alter,  its not just with engine being hot.
turn it over so the oil gets out  of every where.
then with a BIGGG screwdriver,  really press doon on the adjusting screw, this will get the oil oot the push rod tube,
then set at 8
try an eight as standard setting, BUTT also take extra off if there is indents.
also as you set the gaps, as you tighten the nut up, the gap gets bigger,
so needs to be nipped tighter,for it to get bigger,   follow

M

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Your description of the sound and its timing is consistent with camshaft end-play Dave and may turn out to be the cause.
In the 1147 engine it was more towards a light knock than a tappet sound and tended to be somewhat irregular in frequency, coming and going.
I assume the camshaft is held more one way due to the loading of the oil pump when cold but as the oil thins when hot this effect diminishes (as would the cushioning effect on the end-float) and the irregular loading of the cams takes over.
Shimming the U shaped "keeper plate" overcame the problem in my case but possibly thicker keepers are available.  The shim has been in there over 20 years and no recurrence of the sound but it was about 20 thou from memory.  Would not have used a shim if the thickness required was much less in case it broke up as it thinned with wear.
The end float is supposed to be 4 thou.
The sound should be coming from the front of the camshaft if this is the cause whereas the tappet and rocker noises will be at the top of the engine and should be ruled out first, as has been said

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Thanks for all your comments so far. Today I reduced the valve clearances to 6 thou and the tapping noise was just as strong when the engine warmed up. I got my ear as near as I could to the nearside of the engine and it is definitely louder there and in the general direction of the distributor rather than the front end. I wonder if excessive  end float between the skew gear and the distributor pedestal could produce a hammering effect similar to that described for the camshaft above. I think maybe thats my next check and if its not that then its off with the timing cover - I cant wait to have a look inside. Dave

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Perfect65,
The other thing in the same general area which might be the source of your sound is the mechanical fuel pump. You might want to give that a listen too.
                                                                     Best of luck,
                                                                     Paul

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Yes, the lever may be getting very worn,or the cam that operates it.
think some one put a pic up a long time ago,of one worn away  alott.

butt still a good idea to check all the indents on the rockers , then atleast you will have an idea as to what to set your gaps too,.
M

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I would call it a rattle but it only appears at low revs with engine warm. If the engine is raced it runs quietly. When you cut the engine the rattle stays audible with proportional frequency as the crank slows to nothing. I hope that helps describe it. Today I removed the distributor again and put my magnetic stick on the coupling deep inside the pedestal. I would estimate about 5 thou end float although I realise this method is not orthodox but I just wanted to see if there was anything excessive. Would the fuel pump operating lever, if noisy, quieten with revs? I must admit I am starting to think camshaft float or cam chain/tensioner. Thankyou all for your comments. Dave

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One quick way to eliminate camshaft lobe wear, follower, and valve train wear as the cause noise is to get it hot so that the noise is audible. Then take the rocker cover off, cover everything with rags, and stick an 8 thou feeler gauge into each rocker gap in turn, while the engine is running.  That's how I found out it was No. 2 inlet which had terminal lobe and follower wear on my old 1500 engine.

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Thanks for the helpful comments. I have fitted new distributor and the rattle I would now describe as a knock but it still disappears as the engine is revved. So I stopped the engine and re-checked the valve clearances. Number 2 valve clearance had increased and I was careful to make them all the same. Ok, so I started the motor and when it was idling, and knocking, I pressed my big screwdriver down on each rocker, pushrod end, and at number two the knock almost disappeared. Take a bow that man who suggested this. Anyway, next I am taking the engine out anyway so it looks like a new camshaft and tappets, maybe more. I will of course give the valves a look just to make sure one of the unleaded seats is not dropping out. Thanks again everyone and have a happy motoring new year. I will return with news of whatever I find inside the motor next year. Dave

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