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MG Midget and Sprite Technical - Midget tappets

Hi guys

After your thoughts

My 1275 73 midget has really noisey tappets which are annoying me abit now - it has metro turbo rockets fitted -

My 69 Sprite with original rockers has practically no tappety noise so my question is ... Is it the rockers that make the tappety noise ?
If so if I swap the rocker set ups over will this have a chance of fixing the noise on the midget( the midget is the better restored car and want the tappets less noisy on that - any thoughts would be good

Cheers


richard weaver

Perhaps it is the turbo rockets that are making the noise! That sounds like quite a car!!

Mine uses those same solid rockers as in your photo, also with a Metro head, and isn't particularly noisy even though I run them at an increased clearance. Are you sure that the rocker heals -i.e. the contact point with the valve stem - aren't worn? They develop little depressions which make setting the valve clearances deceptive if you are using standard feeler gauges.
Guy W

I thought they were metro turbo but not 100% sure - whatever is in the pic is mine -

It's a standard 1275 first rebore with Kent 266 cam

I guess I'll remove the rockers to see any wear ?
richard weaver

The others thing worth checking for are that the valve springs aren't getting coil bound on full lift and that the rockers aren't fouling on the rocker box cover. The latter is quite common if you are using an aftermarket alloy cover - look on the inside for any slight scuff marks, specially beside valves #1 and #8.

For coil bound springs turn the engine to full valve lift for each one in turn and check that you can see daylight between the coils of the compressed spring - or can slip a 15 thou feeler gauge between the coils.
Guy W

Yes, always check for coil bind when changing the cam, even one with only a small amount of extra lift like the 266. Another way is, with the valve on full lift, push down with a lever and see how much further the valve travels - it should be 40thou+.

A common source of noisy valve gear when clearances are set correctly is worn followers. They should be slightly convex (by a couple of thou) but when worn become concave. This alters the clearance take-up and produces much more of a slap in action - hecne the unquitenable noise.

Another source in performance cams is that the specified running clearance can be just off the end of the ramp. It can make for better performance, but at the expense of noise and longevity of camshaft and followers. If using it principally for a road car then it's worth plotting the ramp and seeing where it ends and opting for a clearance a couple of thou less. This gives you a bit up your sleeve for subsequent wear. The .012 running clearance specified for standard cam profile uses this approach as the ramp finishes at .014".
Paul Walbran

Is the noise coming from the tappets? Are the cam followers/cam ok.
Bob Beaumont

Hi Richard.

I don't think you need to remove the rockers to check for wear at the heels. If you back the adjuster of each valve off all the way with the valve closed I believe you should be able to slide the rocker along the shaft against the locating spring. Once it's clear of the valve and pushrod you should be able to check for wear at the heel pad and on the underside of the rockershaft and in the bush.

Much less invasive than removing the whole assembly.

A mechie's stethoscope is invaluable for positively locating the source of the noise while the engine is running at tickover. It'll help you decide between rocker gear and cam followers for example, without taking anything apart. And there are some inexpensive ones available that work really well.
Greybeard

Those rockers are pretty nasty from a wear point of view. As Guy points out, the valve stem wears a little pocket in the rocker and when you stick your 0.012 feeler gauge in it bridges the wear point giving a false reading. If you use a standard 0.012 feeler gauge but the rocker tip is worn by 0.005 then you will have a noisy 0.017 valve clearance.
You can either replace the rockers with the much harder Midget ones or file your feeler gauge down to the same width of the top of the valve stem. I've still got one in my tool box from my Metro days!!
john payne

That's a neat idea John.
Greybeard

How does filing down the feeler gauge solve the issue -You still need to slide the gauge under the rocker so it will still bridge wont it?
S G Macfarlane

X2 S G
Prop and the Blackhole Midget

X2 S G

I wonder if he means by making it thin side to.side and not the up qand down thickness you can get a more pin point laser focas instead of a broad spread out measurement
Prop and the Blackhole Midget

A lot of feeler gauges are wider than the top of the valve stem so if the rocker is worn you get a false indication of the gap, narrowing the width allows you to check the gap between a worn rocker and valve stem.
David Billington

But the feeler gauge would have to be narrower than the worn indent in the rocker and the worn area would have to extend to the edge of the rocker so you could insert the narrowed feeler gauge - I'm having difficulty picturing it.
S G Macfarlane

If you look at the rocker tip it's not flat but radiused. The rocker doesn't press directly down on the valve, it follows a slight arc and because of that it moves slightly backwards and forwards in relation to the valve. Hence why roller tipped rockers are so good.
Usually the wear on the rocker tip is more in the way of a slot, so inserting a narrower than normal feeler gauge in line with the rocker allows it to go in the slot and take up the wear.

Anyone that thought I meant filing the feeler gauge thinner is a few thou short of an inch!!

Really I should take a photo of my feeler (fnar fnar) and post it on here.

None of this was my idea by the way, something I either read or was told years ago after struggling to set the tappets on one of the 10 Metros I've owned! The tappets seemed to wear nearly as quickly as the rest of the car rusted!!
john payne

A normal width feeler will bridge any wear on the rocker pad and hence give a clearance of feeler + depth of wear [ie greater than intended hence noisy]. If a feeler not greater than the diameter of the valve stem is inserted into the worn groove the correct clearance can then be set.

HTH




Doug Plumb

Nice drawing Doug - a picture paints a thousand words! Thanks.
john payne

Let it be, let it be, words of wisdom, let it be...my only favorite tune by the Beatles...

Following on johns "pic paints a 1000.... "comment
Prop and the Blackhole Midget

This thread was discussed between 08/11/2015 and 10/11/2015

MG Midget and Sprite Technical index

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