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MG MGA - Setting valve lash


Since I can't get to the crank snout bolt from the topside of the engine bay, I'm guessing that setting the valve lash is a two man job UNLESS I have the crank starting handle (one man to "rock" the crank back and forth from underneath the car, the other to observe and call out the valve rocker mid point from topside).

Is this correct?
JM Morris

Hi

I had the same experience, got my hands all scratched and bruised with the spanner slipping off, so I made this helpful tool.
A mild steel bar, 14 mm dia, 700 mm long, on one end a inserted steel piece dia 6mm, long 35 mm, to resemble the engaging end of the crank handle, on the other side three holes drilled approx 120 ° to each other. (2 at 180° might be ok. Too) The second piece is a 500 mm piece of pipe with a 7 mm point welded on, to put in the 120° holes of the “crank” bar, so I can rotate the engine clockwise while watching the tumblers. Works like a charm.


Rik



Rik de Krom

2nd picture

Rik


Rik de Krom

You have a starter button right on the fender. Use it. Forget the way the manual tells you to set the crank and adjust half then reset the crank and set the other half. That is NOT the best way to do it as each lifter is sitting at a different location on the cam lobe. You want each lifter to be sitting on the bottom of the cam lobe. Here is how to do it. Look at the valves with the cover off. If you bump the starter it will stop in one of 4 locations, with the plugs in. In each location one intake and one exhaust valve will be fully closed and ready to adjust. The valves that are ready to adjust are the companion valves to the ones that are fully open. If #1 intake is fully open adjust #4 intake. #1 and #4 are companion cylinders. #2 and #3 are companions.
R J Brown


Thanks, RJ and Rik.

RJ--in my situation, I suspect that my #2 cylinder has a problem and is down on power (possible loss of compression). And I've got one loud tappet--possibly from #2 cylinder. So I don't quite trust bumping the engine to get the exact correct valve position.

What I'm thinking of doing is combining both your and Rik's methods.

If I use the crank handle and use the fully open valve as the starting point, I'm thinking I should be able to turn the crank 45 degrees for the next valve adjustment (360 divided by 8), and then another 45 degrees for the next one, and so on. Does this sound correct?

(By the way, my Haynes manual corroborates your sequencing, RJ. But it says nothing about "setting the crank, adjusting half, then resetting the crank and adjusting the other half". Perhaps that came from the factory manual?)
JM Morris

You could just take out the spark plugs, put the car in gear and pull the car forwards to spin over the engine to wherever you want!
Colyn
Colyn Firth

I take the plugs out and simply turn the engine with the fan. Adjust as per the manual.
Barry.
Barry Gannon


Colyn--if you pulled too far, could you then bump it backwards while still in the same gear, or would you have to put it in reverse?

Barry--tried that. Fan slips. I've got a lot of friction in this engine. I've only had it since February and it's past history is unknown, except that the engine was "locked up" when I bought the car (sat for 2 years unstarted) due to rust rings in two of the cylinders, which I ultimately "powered" through by letting ATF stand in the cylinders for a week.

Rethink on the degrees: 720 divided by 8 = 90 degrees (cam turns 1/2 the speed of the crank)?

Many thanks to all for the thoughts!
JM Morris

Wow, this is complicated!

I always just stick the car in 2nd gear and rock back and forward, don't even bother pulling the plugs.

I do this on all my cars, even the big Jags, never had a problem.

Neil
Neil McGurk

JM, I don’t thing that pulling or turning the engine backwards if you turned a bit too far is a good idea. Independent if this is good or bad for the engine interiors and gears, (since it is being done manually and carefully, I don’t thing it will do much harm) it is important to have all the tolerances and backlash on the correct side, and that is where it is when he engine is running.
I usually adjust the valves in 2 crankshaft turns, as per the manual. It is easier to see when a rocker arm has pressed a valve completely open than identifying it’s top point, so adjust valve 1 when 8 is fully open, 3 when 6 is fully open, and so on, like in the manual.
Interesting to know, is that the numbers of the corresponding valves always add up to 9, so even without the manual, the combinations are easily figured out.
Btw. I made this tool because I don’t have enough room in the garage to push the car, and my fan slips also. This way I can look closely to the rockers while turning the engine without paying much attention to this.



Rik
Rik de Krom

Best way to adjust the valves is to do it with the engine idling. That then gets rid of all the pushing and shoving and trying to work out which valve should be open and which one to adjust. Before starting take the tension off the locknuts then the feeler should be a light drag fit between the rocker and the valve stem. You will quickly be able to work out which valves are noisy as the ticking will stop when you insert the feeler into the slack valve. After completion don't forget to ensure that all the locknuts are tight
Iain MacKintosh


OK--I tackled it today and here's what I found:

I used my new engine crank handle. To use it, I had to jack the engine up since it has settled on it's mounts.

I set the #1 piston on TDC. In that position, my crank handle engaged the crank snout bolt at exactly a straight up (vertical) position. (Don't know if it was designed that way or if it was just a coincidence). In that position, the #4 valve is approaching fully open. It reached fully open at approximately 70 degrees--judged by observing the position of the crank handle. After adjusting it's companion valve (#5 I think), I simply added approximately 90 degrees to the crank handle while watching the next valve due in the sequence (per the manual), and so on.

No pushee, no shovee, no hot oil all over everything, no drama. Easy peesie, simple as pie. I set them at .015 cold (it's a 1600 engine). It was so easy that I ran thru them a second time just to be sure.

BUT--I still have one loud tappet. Can anyone venture a guess as to why? I'm guessing a valve is sticking, for one possibility. (P.S.--after setting the valve lash, I took a compression check and the #1 cylinder is at 50#. 2 & 3 are at 140, and #4 is at 120. Looks like I'm in for a rebuild of the head, engine, or both.)

Many thanks to all for your kind assistance!
JM Morris

Burnt exhaust valve?
Art Pearse

JM, I had a couple of loud ones on my car, cause was a worn rocker shaft and worn bushes in two of the rockers. See if any of your rockers will twist sideways on the shaft. It will usually be the ones nearest the front of the engine as they are the furthest from the oil feed, and sludge build-up inside the shaft can restrict the flow.
Lindsay Sampford

Lindsay--you may have nailed it! I just got thru checking rocker movement. The #1 valve rocker moves at least 10 degrees either direction (frontwards/backwards) off vertical--total, approx. 20 degrees. Couldn't get much horizontal movement. The #2 rocker has about 10 degrees off vertical in one direction. Further, it can't be moved (slid) sideways off the valve. So there's probably a groove in the shaft or bushing.

Some of the other rockers also had excessive movement and/or couldn't be slid sideways off the valve but none as bad as the #1 or #2 rockers.

So I guess my choices are:
a) Live with it
b) Fix the immediate problem (#1 and #2)
c) Refurbish the whole valve train and head and get it over with.

I'm inclined to get it over with. :)

Next will be a leakdown test. I've got what seems to me to be some pretty serious blowby. It's looking like an engine rebuild (groan).



JM Morris

I'm confused (not unusual). You say the No 1 rocker can move 10 deg either way, forward and backwards, but not horizontal. But fwd- backward IS horizontal, isn't it? And does this explain your 50 psi compression on No 1 cyl - does the rocker miss the valve stem?
Art Pearse

Art, it is difficult to describe, but we are talking about a twisting motion of the rocker on the shaft with wear rather than the sliding horizontally up and down the shaft against the springs.
Lindsay Sampford

To help visualise this a little better, place one end of a ruler on top of the rocker arm over the shaft, one finger on the top of the ruler to hold it in place. Now rock the ruler rearward then foreward 20 degrees. That's twist in the vertical plane.

If I lay the ruler down flat on top of the length of the rocker, then turn the ruler fore and aft in a circular motion (central axis is the rocker shaft), then I have twist in the horizontal plane.

Or, I can attempt to slide the whole rocker (rather than twist it) along the length of the rocker shaft (horizontal plane).

Art--I wish and hope this would explain the 50 psi compression, but I doubt it. The valves are reaching their full height when closed so not sticking. Now if I have a burnt valve as you suggested, that could be a possibility. I'll cross my fingers. I'd rather it be that than the rings, but there's an awful lot of blowby in this engine or at least more than what would seem normal to me.
JM Morris

Thanks for the clarification - certainly a badly worn rocker or shaft. Good luck with the teardown.
Art Pearse

Blowby indicates a piston/ring/cylinder wall problem. A burnt valve won't cause blowby. Blowby is compression going past the rings into the crankcase and out the breather at the top of the valve cover and at the tappet cover vent/downdraft tube.
R J Brown

JM, have you tried a squirt of oil down the plug hole of the low compression cylinder? If it improves the compression you have a ring/bore problem, if it makes no difference it's a valve not seating properly.
Lindsay Sampford

I think that 50 psi is too low to be just piston rings.
Art Pearse

Lindsay--no, haven't tried that. But I'll be doing a leakdown test this weekend and that should solve it. If it's an intake valve, I'll hear/see it through the carbs. If it's an exhaust valve, I'll hear/see it through the tail pipe. If it's the rings, I'll see it out the downdraft tube/breather tube.

Art--sure hope you're right!

Now let's see--after checking #1 at TDC, I should be able to turn the crank handle 180 degrees to get the next one (#3) with valves fully closed. ;)

--Jack
JM Morris

Update: Bad news--leakdown test results as follows:

#1--85%; #2--20%; #3--21%; #4--37%

All leakage was past the rings. Nothing detectable at the carb mouth or exhaust pipe outlet.

I have heard that a new car has leakdown of about 12-17%. If that's true then #'s 2 and 3 are in relatively good shape.

Apparently, #1 and #4 were the cylinders with the rust rings.

Which gives the most accurate reading--a hot engine or cold engine? Mine was hot when checked.

My buddy has a Bugeye with a 1275 in it that he had special rings put in. The manufacturer claimed a 1% leakdown result. Out of curiosity, we checked his #1 cylinder cold and it only had 4% leakdown. Amazing.

So now I've got to prepare for an engine rebuild. Wish me luck!

--Jack
JM Morris

This thread was discussed between 15/06/2010 and 26/06/2010

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