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MG MGB Technical - Valve Adjustment Specs

My manual calls for adjusting the valves at 17 thousands / cold. However, I still have valve chatter. Should I be adjusting them closer?

BTW,...my car is a 1970 model.
Danny T

Danny,

If your engine is a 18V and later, it is 0.013" warm clearance and for an earlier engine !8G series 0.015" cold

Cheers,

Jean
Jean Guy Catford

A lot depends on what Cam you have fitted as well (the Piper 270 runs at inlet 0.016 and exhaust 0.017)

But the B has always been a noisy engine!!
K Harris

"a noisy engine is a happy engine"

Get yourself a ClikAdjust Danny, it'll make adjusting valves a lot easier and will be more accurate.
Mike

Danny, if your rocker ends are worn then you will get extra clearance than what you measure as the feeler gauge bridges the wear groove. You should remove the non-contact ridges on an oilstone so the rocker end is flat across its width.
Art Pearse

How are you adjusting them?

As has been said B-series engines were always noisy. I found it very difficult to get repeatable clearances on mine - I like to do them through two rotations of the crank then check them again through another two. Eventually I found that at the strict 'rule of nine' points some valves were still changing, having larger clearances either before or after that point depending on the valve. Since I started adjusting them at the largest gap point not only is it repeatable but they are also noticeably quieter. It's been several years now, and very rarely do any ned altering, so they aren't recessing either.
Paul Hunt

Paul,

For what it is worth, Delta Cam, a cam grinder in Spokane, Washington, USA, told me I should adjust the valves when the cam follower is opposite the high point of the lobe, and that I should ignore the extra clearance closer to the lobe since that part has to do with ramping.

Charley
C R Huff

If it were the same on all valves that would be a fair point, but as it isn't on mine at least I'll stick with adjusting them at maximum clearance. I'd be interested to hear from others if their clearances are changing at the 'rule of nine' point or not, as I don't know which of mine are 'correct'. I'd be surprised if that is the norm, it would mean that everyone would have the same problems checking and rechecking clearances, and I've not heard anyone else say that.
Paul Hunt

Paul,

Next time I adjust mine I'll pay particular attention to see if they remain constant, but I think I usually do that anyway just to see if I did something out of order.

In part, I think the problem could be that the rule of nines is a bit imprecise because it is a visual observation of full open. Quite a few degrees of crank rotation can still result in a valve being visually fully open. I think it would be more precise to adjust based on turning the crank through a specified number of degrees while progressing through the valve adjustment.

Charley
C R Huff

We are all assuming that every cam produced is perfect and will result in an accurate rule of nine adjustment. An old saying that comes to mind: Perfection is a goal, not a reality. RAY
RAY

I set mine by the rule of 9, and by reducing the valve clearance to zero (determined by twisting the push rod with my fingers, when I cant twist it anymore, I take it as being zero clearance. I then back the screw off 1/4 turn and tighten the nut. Apparently the thread pitch and rocker ratio (1:1.4 from memory) equates to 15thou clearace at the valve.

I check it every year and always find zero clearance comes up at 1/4 turn and always end up putting it back to where I found it. I only do 3-4000 miles a year.
Chris

"Quite a few degrees of crank rotation can still result in a valve being visually fully open."

Precisely (pun intended) so. I sort of assumed that the rule came about because that put the valve being adjusted on the back of its cam, so quite a few degrees of cam movement makes very little difference, but I've never checked if that is the case. If not then it's hard to see how the rule came about if it gives such an imprecise point of adjustment, and hence significant variability in clearance, nor why it is so often quoted as the correct way to it. As I say, with only one engine engine to go by I have no way of knowing which of my valves are the norm - the ones that don't change around the rule of nine point or those that do.

Chris's method is the theory behind the ClikAdjust, but personally I wouldn't want to keep slackening and tightening the screw and nut every time.
Paul Hunt

Hi Paul

I use rule of nine then chase any noisy ones using a 12 thou feeler guage with the engine running.

Peter
peter burgess

Do you know (surely you do?) where the tappet is on the cam when adjusting a valve to the rule of nine?
Paul Hunt

The back is ground circular for almost 180 degrees, so it is not important to be so exact.
Art Pearse

John Twist of University Motors has a great video on you tube about adjusting valves...

http://www.youtube.com/watch?v=fezXUwVfH7U&feature=PlayList&p=CFB510794339861C&playnext=1&playnext_from=PL&index=9
Bob Dougherty

It may sound odd if you have never heard of it, but old time mechanics (at least on American iron) often adjusted the valves while the engine was running. This was taught to me by an old timer when I was adjusting the valves on my 46 Chevy truck (though it has the more modern 235 CI engine from a 54).

You just slide the feeler gauge, and it will move in jerks if there is clearance greater than its thickness. If the clearance is less than the feeler gauge thickness, it locks in place and stops moving. So, the tip point between locked and moving in jerks is the setting. With the engine at an idle, you can work the tools on the adjuster and lock nut.

It can make a bit of a mess with spitting oil, but not bad on the engines I have done it on. I never tried it on my MG, but I’m sure it would work and it takes all the guesswork out of where to position the engine for the adjustment.

The other advantage, if you believe in doing the adjustment hot, is that the engine is not cooling down while you do it.

So, try it, you might like it. If you have wear on the tips rocker arms, all bets are off.

Charley
C R Huff

Charley,
I used to watch my father adjust the valves with the engine running when I was a child. When I got older, I looked back and thought to myself that he just didn't know how to properly adjust valves. Now that I hear you say old mechanics used this approach, maybe my dad knew what he was doing.
Cleve

Paul, I to have found a similar situation to what you describe above, in other words, if you check/adjust clearances by the rule of 9s, then repeat, you have found differences. Now you seek the greatest gap on each, and adjust to 0.013" warm, correct? Do you just seek the largest opening following rule of 9s or just rotate the engine so that you can measure the largest clearance of each valve and adjust if needed?

Also, I too remember watching my father adjust valves on Chevy engines as a young child with the engine running. I remember being fascinated watching the action of the valve train and his hands with a feeler gauge and wrench adjusting each. That was nearly 45 years ago but the image is still clear.
Joe

Cleve,

I am glad to have reinstated confidence in your father's know how. I guess it's a delayed case of your parents getting smarter as you get older.

Charley
C R Huff

Charley,
I've done valve adjustments with the engine running, it was the workshop manual method for cars I used to service, I think it was Opel, gravey boat rockers any way. It seems to work but chews up feeler gauges.
Paul, I too found the same discrepency as you, but this was on an aftermarket cam, there are a lot of poor products about. A friend of mine had a rebuilt engine fail while in France. That was down to bad cam and followers. A rolling stone gathers no....!!
Al
ALLAN

DON"T try that with a T Series!!! The oil will shoot up to the ceiling!!!!
Bob Dougherty

What actually changed in the 18V that requires them to be adjusted .013 warm instead of .015 cold?
Steve Rechter

Steve: I don't think it was any more than trying to get the valve adjustment a little more accurate to help the emissions issues. If you adjust the valves on an 18v engine at .015" cold, you will find that they are about .013" when the engine is warm.
John Perkins

Nothing, and as the manual didn't specify what 'warm' was I don't see how it could be more accurate than .015 cold, less so in fact. If they had said .013 at normal running temperature that would be different, and then give you the problem of maintaining that temperature throughout the adjustment process.
Paul Hunt

I don't suppose the factory defined cold either. The problem I find is that as soon as I start an engine it starts to get warm and the tappet settings vary too. I find it easier to have a warmed up setting as a srarting point. Failing warm settings I tend to take a guess and drop the cold settings by 2-3 thou. Just to throw a spanner in the works, I get the best bhp with a standard cam when the inlet tappets are set 10-12 thou warm and exhaust tappets set at 15 thou warm, seems to give the ex valve a little longer on the seat to cool down.

Peter
peter burgess

You'd be amazed at how much the valve clatter quiets down
after the rocker shaft has been checked and (if necessary)
renewed.
Daniel Wong

Peter,

You are effectively increasing the inlet duration and reducing the exhaust duration marginally - I would have thought that has more effect on power?

The difference between cold (say 60 degrees F) and running temp ( say 190 degrees F) is 130 degrees - the difference in expansion between the cast iron block & head and the steel pushrod is only 0.17 thou over this temperature range (0.24 thou at the valve allowing for the rocker ratio) which suggests that the majority of the difference between hot & cold valve clearances is due to expansion of the valve stem.

I would expect the inlet valve to run significantly cooler than the exhaust and there should be a greater difference in setting for the exhaust valve clearance between hot & cold.

Chris at Octarine Services

I have seen shop manuals (not BMC, but something British) that defined "cold" as 70F, and that is standard for precision measuring situations, like machine tool rebuilding. It's all silly, "cold" could be anything from -30F to 120F, and "hot" anywhere from 140F up. So cold covers 150F, hot about 100F, and the minimum difference between cold and hot is 20F. Royal Enfield defined it as "ambient" and I did change it summer to winter, because the settings were "inlet, zero, tight; exhaust, zero, loose", and the differences in that were clear at various ambients. That is an aluminum engine, aluminum heads, with aluminum pushrods, and iron barrels.

Paul O'Donnell, The guy I worked for at the beginning of my professional British car life c1966, was the service manager at the Pittsburgh area dealership. He was thought of highly enough that the BMC factory chief tech rep scheduled all routine maintenance on the C diesel engined Tech School bus to be done by Paul on their country wide teaching tours.

One day Paul pointed out to him that the factory had variously stated that valves were to be adjusted "cold" "warm" and "cold running", all at the same number on the same engine. The Tech guy couldn't explain it, so they measured it in various states and decided that it didn't vary enough for anyone but a labfreak to consistently measure it.

I went and measured a bunch of them in various states and agreed, and I've never worried about it since, on an iron/iron engine. I usually don't set the valves outdoors in the dead of winter, or on an engine that is blowing all its coolant out the pressure cap.

It's ALL silly, for normal street use. What's the material of the no name valves that were just put in? How many people can repeatably measure a +/- .0005 variation, and if you find two such people, what are the chances they agree on the number? Are all the parts new? How thick is the oil film(s)? A standard "Go- No Go" valve adjustment feeler has a step of .002, with the thin bit roughened so it can be felt if tight. A ".015" feeler is .014 and .016)Get all the clearances pretty equal and as close as you can reasonably get to the spec, and relax.

On the original discussion, the "rule of nine" is exact, and if the results are not, then either the cam or the operator is out of spec, in which events it is still not worth worrying about, so far as engine life is concerned. If your are building a race engine, or a Rols Royce, the parts, and therefore the measurements, will be right or you get sent back to school.

I find it interesting that Peter's measured optimum power settings are exactly what I arrived at years ago, by theory and feel.

FRM
FR Millmore

Hi FRM

As I asked the other day were these on a dyno, rolling road or seat of the pants? I agree re 'what is a fit for a feeler guage' my 11 thou seems to be most peoples 10 thou as I make sure the feeler guage is a tight push.It is just that Bs tend to be noisy and are quieter with well adjusted tappet clearances, that is why I do my clearances hot, especially when chasing an occasional loud one.

Chris, I do know the reason for the increase in bhp, just wanted to tell folks that the figures of 13 thou cold and 15 thou hot aren't gospel.

Peter

peter burgess

"On the original discussion, the "rule of nine" is exact, and if the results are not, then either the cam or the operator is out of spec, in which events it is still not worth worrying about, so far as engine life is concerned."

Quite, which is when when some of mine are one side or the other of that, it doesn't bother me, I adjust at minimum gap to reduce noise and get repeatability.
Paul Hunt

Hi Peter-
No dynos, no rolling roads, just lots of study, experimentation and thousands of runs up the same roads in similar cars. Really screwed me up when I moved!

Re SU, I was hired on PJ OD's recommendation, by the Pittsburgh Volvo/Triumph dealer C1968, specifically because the founder was tired of hearing from customers that their cars didn't run because none of the 10 mechanics & service manager knew how to set up SUs. So he overrode his son's running of the business, and hired me to be the carb guy. I figured I should learn how they really worked, so I did. No more customer complaints while I was there. I keep up the study still, and I'm still finding new fine points, like the elegant Rover part throttle lean out system.

Rolling roads are almost unknown in these parts. Emissions requirements got them into Pennsylvania state inspection stations, in some areas, but generally all those people want to do is check emissions, and they quit using them when OBDII came in.

Google search for "rolling road" only gets UK places; "chassis dyno" turns up many more manufacturers and distributors than places that actually have one you can visit, don't know who they are selling to. I've found a couple that are about 200-250 miles from here.
If I could come up with the upfront cash, I often thought of mounting one in a truck so I could take it to race & club meets.

FRM
FR Millmore

Hi FRM

Looking at my post I meant 13 thou hot and 15 thou cold and cannot spell gauge :)

I was looking at some of the mobile dynos...turns out some have gritted rollers to get quick readings....no good to me and explains why many new dynos seem to give low rwhp and similar flywheel hp as we guesstimate. Had a V8 recently showed 153 or so rwhp on a dyno dynamics dyno giving 195 flywheel bhp, we gave it a quick run at 165 rwhp, pinking it's head off in a dangerous manner, may have shown a little more rwhp but I was nervous. My guesstimate is rwhp 165 plus 12 for tyre losses then 10% for transmission, gives 194.7....close to dyno dynamics? But took me longer to bed in tyres and get 'proper' readins and the knowledge that the engine tune was unsafe.

Peter
peter burgess

Peter-
Gauge is a pesky one, do it all the time myself.
So, with a modern high powered good rubber car on gritted rollers, you have a 12hp rubber grinder = $200 dyno time and $1000 in tyres! But you save the engine.

FRDM
FR Millmore

At the risk of extending this thread forever - on a rolling road, what is the difference in tyre losses on the rollers vs on a flat road? And how can you tell?
Art Pearse

Charley,
While it doesn't change what you said, Delta Cams is in Tacoma, WA about 50 miles from me, Spokane is about 250 miles east of Tacoma. I have been using their services for almost 40 years.
Leland Bradley

Hi Art

We have polished steel rollers...Texas oil pipe I understand is what Mr Clayton used :) the original smooth grey enamel style paint has long gone, it takes a gently increasing load run of a minute or so to bed tyres so they grip. I fear some of the new dynos maybe tyre shredders in the interests of quick buck power runs. The grip is not as rough as a 'normal' road surface or the tyres wouldn't have to 'bed' in to grip :)

Peter
peter burgess

Leland,

Right you are. Thanks for the correction.

I feel better now. A few years ago I drove to the west coast, and unexpectedly found myself within about 40 miles of Spokane. I was kicking myself for not throwing my MG cam in the car with me because, after returning home, I had to mail it to them.

But, since they are in Tacoma, I wasn't near them anyway. Good thing I got it right when I addressed the package.

Charley
C R Huff

To get back to the thread, The reason valve adjustment can be different the next revolution or two on is that the lifters rotate very slowly and stop at a different point of contact each time and its slight lifter wear that causes the problem. With a new cam and lifters this does not happen if setup correctly. The reason adjusting the valves running gets the engine quiet is because the lifter is turning faster and you can feel the maximum slack as if its there all the time. Back when I started as a mechanic almost all OHV were set running unless they had bucket type followers. Its not hard to do when you get used to it but easier still with two, one on the screwdriver and spanner and the other with the feeler. You may find this hard to believe but the way some (not me) stopped the oil spray was to drain the sump and do the adjustment quick.
Denis
D M HILL

"The reason valve adjustment can be different the next revolution or two on is that the lifters rotate very slowly and stop at a different point of contact each time and its slight lifter wear that causes the problem."

I don't doubt that can happen, but the non-repeatability on mine is purely down to the fact that the gap is still changing at the strict rule of nine point, and on the same valves every time. When I adjust at the widest gap, either slightly before or after the rule of nine point depending on the valve, it is always repeatable and consistent. It's always the same valves, and always the same direction and amount on those valves. So in my case nothing to do with variability of lift from the followers as they rotate.
Paul Hunt

The point of valve clearance is to ensure the valve stays shut when intended. The clearance was presumably calculated with the maximum likely valve growth due to heat. They were not chosen to keep the noise down. To my mind it is not good to try and find the loosest part of the back of the cam as the place to set the gap.
Art Pearse

"The clearance was presumably calculated with the maximum likely valve growth due to heat."

Doesn't really make sense when the cold gap is .015 and the hot gap .013. You would need six times more expansion than that to get near the zero clearance of hydraulic tappets.
Paul Hunt

Paul, "hot" when doing the valves is not really hot, due to cool down time. The valves will cool off in a matter of a minute or so from stopping the motor. Also, running full bore would be considerably hotter. Hot and cold when actually adjusting valves are about the same situations. Anyone know how hot valves actually get? (tip and stem)
Art Pearse

This thread was discussed between 05/07/2009 and 26/08/2009

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