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Engine Noise

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bison
Posts: 14
Joined: Thu Mar 03, 2016 10:17 am

Engine Noise

Post by bison »

Hello Folks,
Just back from an epic and enjoyable drive to the Pyrenees and back in my SP from Scotland, the car performed perfectly, even in 32C!.
So, the noise!, it's been there ever since I got the car, not getting any worse, or better. It 's a hollow knock, it seems to be coming from the distributer drive area, and it gets quite noticeable above 3000rpm, worse when cold, but quieter when hot, there at all revs, and easily heard at tickover. I've had the stethescope on it, and it's definitely from the distributer drive area. The engine is rebuilt, good oil pressure, mains, big ends pistons all good. It's not piston slap, small end or big, the car as I said drives superbly, and in over 10K miles the noise has not got any worse. I thought when I first built the engine it was a noisy/loose cam follower ball, but thanks to Geoff Douglas I replaced those, and the cam chest too, no difference. I remember watching a You tube video of someones rebuilt SP running, and it had exactly the same noise, but unfortunately I can't find it now.
Is it possible the distributer drive gear has too much vertical movement?, IE the distributer drive dog and gear have too much clearance and the gear is clattering up and down while the engine is running?.
Any constructive ideas gratefully listened to.
Thanks,
Alan.

Bud
Posts: 318
Joined: Fri Feb 12, 2016 9:06 pm
Location: Rochester, NY

Re: Engine Noise

Post by Bud »

Alan,

If you suspect the gear for the dizzy to be suspect, take the cap off and see how much play is in the lash by twisting the rotor back and forth and pull it up and down. That should make matters a lot clearer, if there is ANY motion over a degree or two its time to look at the gear and hope it is the dizzy and not the cam gear that has "made the space" or rattle between the teeth and causing the drive to go up and down.
Good luck.

tjt77
Wise Man
Wise Man
Posts: 525
Joined: Wed Mar 23, 2016 7:01 pm

Re: Engine Noise

Post by tjt77 »

One common rule to help diagnose :- parts such as con rod, main bearings and pistons that have excess wear sufficient to be audible at some speeds, will change in pitch and volume depending on engine load..
parts such as valve train remain consistent regardless of load on engine.. the pitch changes with engine speed.. also these parts run at 1/2 the speed on the engine.
you can generally gauge the condition of crankshaft bearings via oil pressure.. if it remains consistent between hot and cold temps the lower end is generally sound.... if the pressure is 45lbs or above when cold and less than 35lbs when hot @ 2,600 rpms its usually due to worn crank bearings..

Without actually hearing the car run, its very hard to diagnose.. the bronze dizzy/oil pump shaft gear is subject to wear .. but it should not make excessive noise as you describe, even when well worn..you state the the engine was rebuilt and cam followers were replaced.. the most common source of upper end noise, is wear of cam and followers.. very often there are blockages in the oil feed to the upper end.. most commonly between the actual rocker and the adjuster and usually within the hollow adjuster itself (heat will cause the carbon suspended in the oil to solidify if regular oil changes are not adhered to)..oil flows form fed pie at back of engine, through the rocker shafts and through feed holes in the rocker shaft, into the rocker....and exit via the end of rocker (on inlet side) as well through the hollow adjuster and out through the ball end into the push rod on both inlet and exhaust sides.. if one or more of the push rods is not getting oil it will clatter..
Ive encountered a LOT of them that have 'rebuilt' engine...but the valve train remains knackered because the builder went over budget and assumed the cam and accompanying parts would be Ok.... all it takes to get audible is a few scores on one of more cam lobes that are sufficient to alter the profile of the 'ramp' on the cam or a pocket one or more followers (these should have an even curve on them and are relatively easy to re-surface..the stellite facing is visible and quite thick )..the flowers also wear in their slides (a very common problem) ..both follower shaft and bushing are subject to wear..(most have a bronze bushing in there) and if they have ANY side movement will make an audible noise..

when in good shape the valve train should be inaudible.. any clacking is due to wear or poor oil feed ( which will lead to wear rapido) or a combination of both..

One very messy test is to remove the rocker covers one at a time, and run the engine to determine if all the rockers have an even feed.. it helps if you have strong torch and a magnifying glass..
(such as those used for reading topographical maps)...you should see oil coming out of the holes in ends of inlet side rockers .. and oil dripping out of the top end of the push rods ..and it should, be even on all 16 ...
good luck.

bison
Posts: 14
Joined: Thu Mar 03, 2016 10:17 am

Re: Engine Noise

Post by bison »

Many thanks for the constructive replies.
The problem has been solved. Upon inspection of the drive gear and clearance everything was spot on. I turned my attention to the distributer itself. When stripped it revealed the primary bob weight spring (which i had replaced) was either stretched or was the wrong one. It was allowing too much motion on the bob weights, which were clattering about. I'm lucky enough to have a spare distributer, I checked the weights and springs on this and found the difference to be the springs. I then swapped the both springs around and refitted the distributer, the noise has gone!.
I think it sounded much louder because of where it's located, in a nice bell shaped chamber!, and of course it would echo and be amplified in the cam box.
I hope my findings might help some one who is having a similar problem.
Thanks,
Alan.

Fossil
Wise Man
Wise Man
Posts: 516
Joined: Sat Feb 13, 2016 5:08 pm
Location: Helensburgh, Argyll

Re: Engine Noise

Post by Fossil »

Alan

Good to find your post, delighted that you've had a brilliant holiday, and esp that you have eliminated "that" noise. I've always found the arrangement of those little springs bizarre, and its impossible to remember it clearly when they've been disturbed. Thanks for the thanks, good to know that it was useful.

Will you be coming to Peebles next year? (see events section), it would be good to see you there.

Cheers

Fossil

bison
Posts: 14
Joined: Thu Mar 03, 2016 10:17 am

Re: Engine Noise

Post by bison »

Hi Geoff,
Now that the distributer has been "disturbed", I'll go through the points and ignition timing again.
I hope to get to some of the rally at least, some of the day trips should be possible. Peebles is just down the road for me really., about 40 miles.
Alan.

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