MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG TD TF 1500 - engine knock

I have an intermittent knock in my engine. any other engine I would say a small end bush.
It seems to happen both as the engine warms up or for a few minutes after a long hot run. It is not a sticking valve and not loud enough for a big end, not detonation as it happen at tickover.. The strange thing it is not there all the time. No change in oil pressure or performance.
Any ideas?
Ray TF 2884
Ray Lee

As my uncle (an indy race car engine builder) taught me. Take a piece of hose, put one end in your ear and touch it to various areas of the engine to see if you can better pinpoint the area of the noise.

That will assist in diagnosing what it is.
Bruce Cunha

I used a stethoscope but was unable to place the sound. I even ran it with the rocker cover off ( oil line isolated) to no avail.
Ray TF 2884
Ray Lee

Next time it's ticking pull one spark plug wire at a time to see if you can make it go away. Wear gloves.

If it goes away it's most likely the wrist pin (small end) on that particular cylinder.
L E D LaVerne

Ray
I chased a noise like this with an MGB and it ended up being (after much searching) a cam follower, hardly had a mark on it but that was what it was---------
One thing for sure is it won't be a little end bush

and by the way, if you're pulling plug leads off with the engine running gloves aren't enough you need a pair of plastic pliers, not insulated metal pliers either,---- plastic pliers are the go
Cheers
willy

Bruce---got a story for you
Trying to find an exhaust leak on a F series ford ambo. one day and got the rubber hose out, working along the exh. manifold and then BANG , an almighty whack in the ear and the smell of burnt something--It turned out that the rubber hose had metal braid in it and i got shorted out on a spark plug--won't be doing that again by crikey
William Revit

Willy - I sympathize. I was at an automotive swap-meet (jumble) about 40 years ago, and was drawn to a Lucas magneto. I picked it up and was talking with the seller, and absent-mindedly spun the gear to be sure everything was free. The plug wire must have been touching my arm, because I got the most God-almighty big shock from the mag, the closest to being Tasered (don't ask how I know...). I literally could not move, think or speak straight for an hour.

Like a handgun, I now treat every magneto as if it was loaded!

Tom Lange
MGT Repair
t lange

I hate electric shocks. It is the one thing I really try to avoid. Unfortunately, they still happen.

We are rebuilding a 1921 Cleatrac tractor. Engine is done, we added the magneto and one of the wires fell off the spark plug. I touched the body while we were cranking it and wow did I get a jolt.

Ray. An automotive stethoscope should help. They tend to be more specific than a hose.

From your description of it being intermittent, it does sound like a part that is under oil pressure.
Bruce Cunha

When I was doing my apprenticeship (a long, long time ago) one of the training aids was a flat-head Ford engine on a stand. One instructor would lay both forearms along the plugs and stop the thing running. I never attempted it!
Ian Fry

LaVern,
I don't think it will be the little end as the gudgeon pin runs in the piston and is clamped to the con rod. If the clamp was loose it would be noisy all the time and destroy itself the way I drive.
Mind you, many years ago I heard a noise and a drop in power. Got towed home, no compression on No3, took the head off and found 3 pistons at TDC!. The piston crown had snapped off at a ring groove leaving the bottom half of the piston to continue up and down the bore.
Ray TF 2884
Ray Lee

Hi Ray
I had a similar problem with my TD. Had an intermittent knock which over a short period of time became more regular. On stripping the motor I found that the case hardening on one cam follower had failed and damaged the corresponding lobe on the camshaft.

Before going too far it would be worth removing the rocker gear and tappet inspection cover, then pulling out each cam follower in turn to check their condition and corresponding cam lobe.

Good luck. Rgds John W
John Winzer

John,
that is the next step, at bit dubious though as my tappet clearances have not changed.
I am just putting off the day I have to take the lump out. You think for days with a TF before you attempt to take it out, what is an afternoons work on a TD is a nightmare on a TF, just getting the clamps and hoses off is hard.
Ray TF 2884
Ray Lee

And another strange engine noise story. Back when I was wrenching we had a TD with a strange continuous tick or knock. When we pulled the sump we could see the con rod had bent just enough to touch the lower edge of the bore as shown by a shiny area on the rod. Apparently a hydrolock situation caused this.
John Quilter (TD8986)

Shot in the dark, but several have mentioned a knock when the oil pump circlip fails. George
George Butz III

Ray
Been thinking about this noise and that it changes with temperature----Could it be a crack in the fan belt--Had one in the belt on an MGA once and it was a deep and meaningful noise that came in and out with temperature ,it was deep enough to make me think the front pulley was clonking on the keyway at idle and sounded a bit like a lighter bigend noise at high idle speed-
Started pulling it apart to check the pulley and saw the crack in the belt, started it up without the belt and -gone, fitted a new belt and all was good---
willy

Tom
Been tazered eh, you must be a naughty boy-
I've been whacked a few times specially them impulse mags., setting the timing and then bang-bugger gotcha, but please guys, be carefull, you can't be too carefull around electrics, especially around later cars, the end result can be fatal or very damaging to you-----
Safety Fast
willy
William Revit

William, I don’t know if you are old enough to remember phones where you turned a handle to attract the attention of a young lady at the exchange. I am.

The device turned by the handle can attract attention if connected to a urinal. Do NOT ask, even though the statute of limitations may have expired I will deny everything.

Cooroy Primary School, Queensland, Australia.

Whilst this was not a magneto, it worked on the same principle.

I ain’t gonna put my name in this.
P G Gilvarry

Remember them quite well PG
William Revit

Cam followers.
One not rotating fully all the time giving false clearance readings.
Two worn slightly dished.
Five pocking.
Camshaft does not appear to be spalled, same lift on all lobes. So it is new followers (cheap enough) and see what I hear.
Cam and followers have about 90,000 miles so I should not complain.
Thanks for all the suggestions.
Ray TF 2884
Ray Lee

Hi Ray. Well at least you have got to the bottom of the problem.
I see you are only intending to change the cam followers and not the cam??
Rgds
John W
John Winzer

John,
The cam appears to be undamaged both by measurement and visual. If the knock is still there I will then take the engine out and inspect.
As I said earlier, TF owners do not attempt to take the lump out unless absolutely necessary.
I have had a TD engine out and in twice in the same day.
On a TF it is 2 days and a visit to an A & E department.
Ray TF 2884
Ray Lee

Hi Ray.
As you can guess, never had the pleasure of working on a TF. Wish all goes well.
Rgds
John W
John Winzer

Measure twice, cut once.!!!!!!!!

I just did the hot tappet settings and noticed one valve not going down quite as far as the others.
I must have misread the DTI gauge when I checked the cam. It still runs OK so I will leave it till the roads are salted and then take the engine out.May be I will cure some of the oil leaks :-}
Ray TF 2884
Ray Lee

Hi Ray
Thanks for the update-
Apart from the now diagnosed cam lift problem, Although it runs OK, did the new followers eliminate the noise problem---just interested in the result of that
William Revit

Yes the new followers cured the noise but I know the cam will wear further but I will probably only do 6/700 miles before strip down.
At the last rebuild 90.000 miles ago, the cam thrust plate was carefully shimmed to position the cam shaft. This is done to ensure that all the cam lobes are off centre of the followers to make sure that they rotated.Number 8 follower had stopped rotating fully and had a tramline in it.
I probably checked my tappets on the unworn part when I was chasing the noise.
Any way I will give me something to do this winter.
Ray TF2884
Ray Lee

Thanks Ray
Yeah really important to make sure the followers are free to rotate
Sounds like you're onto it though positioning the cam as you have
There's a bit of confusion about concerning the base shape of followers with some believing they should be dead flat and others believing they should be the normal slightly convex shape
When you get your new cam or have yours rebuilt it might pay to ask the supplier what their recomendation is for their grind and have your followers ground to suit

Some research for you to get into---

I have heard of people grinding tiny slots/flats down from the relief holes in the sides of the followers through to almost the bottom of follower to supply a bit extra lube to the lobes--Don't know if it'd be worth the hassle but interesting all the same

willy
William Revit

I will be getting a fast road cam from the Octagon Car Club with its matching nitrided followers.
At 82 they should see me out.
Not looking forward to pulling the lumo out but it has to be done.
Ray TF2884
Ray Lee

Hi Ray
Good to know you have got to the bottom of the problem.
I got my new cam from Brown and Gammons. It was their Cross Drilled Fast Road Cam and followers. When it arrived I discovered it was manufactured in UK by a company called Newman.

They recommend larger valve clearances with that cam so the valve gear does sound noisier.

Also there is a reduction in indicated engine oil pressure due to the cross drilling. The upside is that there is a lot of oil now directed at pressure on to the cam lobes and follower faces.

Very pleased with the result.

Good luck with the winter project.
John W
John Winzer

This thread was discussed between 27/09/2021 and 16/10/2021

MG TD TF 1500 index

This thread is from the archives. Join the live MG TD TF 1500 BBS now