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MG MGB Technical - Valve Lash Adjustment problem

Hi All,
I can't seem to get rid of the tapping even after adjusting the valve lash 3 times now. This last time I even adjusted it a few thousands of an inch tighter then specs. I did adjustment (cold) to .012.

Car is a 1972 MGB-GT with an 18v engine.

I also notice that the valve adjustment nut on a couple of the rockers is only holding by a couple of threads and would not be able to adjust the valve lash any tighter.

Could it be worn parts? I have a spare set of used push rods, lifters and a spare used rocker assembly. Thougth I might try swaping the rocker assembly and the push rods. I don't want to go as far as swapping the lifters at this time as that would require much more disassembly of the motor. (carbs, exhaust manifold and tappet covers etc.)

If it is just worn push rods, can anyone give me the exact measurement of the length of a brand new push rod so I can compare it the the length of the ones I currently have.

Any advice would be much appreciaed. I have a 3000 mile trip comiing up in two weeks.
Car seems to run well at this time but I worry about the adustment nut only on by a couple of treads and am also concerned with the loud tapping sound.

John Fraioli
John Fraioli

Likely valve train wear. Start with the easy items such as rocker tip, shaft/bushings, or pushrods. If they're okay suspect lifters and probably can.

Valve seat wear would tighten so that's not it. Unlikley you get enough deposits on the valves to increase clearance.

I suspect lifters/cam.
Robert McCoy

John, It does sound like rocker tip wear with the possibility of some cam wear.
Try setting the clearance using a different but less accurate method. By this I mean screw the adjuster in until it touches the valve stem then back it off until you can get a .001 feeler in, now do it again with a .013 gauge and note how far you have turned the screw out. The amount the screw is turned between the measurements is the amount needed for the correct setting. Now screw back in until you touch the valve again and back off the screw the measured amount of turns.

This next suggestion is a bit radical... If the adjuster screw is well in to the rocker such that you can't get the lock nut to hold, is there sufficient room to put it under the rocker without interfering with the movement or the top of the push rod? Never tried it my self but desperate times.. Failing that use a locking fluid such as loctite and leave the nut off.. Told you it was radical...

BTW where you going on a 3k trip?

MGmike
M McAndrew

John-
It's not the pushrods. There are two likely causes of your problem:

1) The thrust pads of the rocker arms have become deeply grooved. This can be checked by loosening the adjuster of the rocker arm for #1 intake valve (the second one back from the front end of the engine), and moving the pushrod out of engagement with the rocker arm, and then lifting the opposite end of the rocker arm and examining it.

2) The rocker arm bushings and rocker shaft are badly worn. After performing the above operations, slide the rocker arm back against its spring on the rocker shaft, and then use your fingernail to scrape along the underside of the rocker shaft. If you feel a ledge, then the rocker shaft and the rocker arm bushings will need to be replaced. Incidently, this is the most wear-prone part and the most common source of a noisy valvetrain of the B Series engine of the MGB.

From what you've described, I wouldn't be surprised if both conditions exist on your engine. Once restored to proper condition, the valvetrain will make a nice click-clack sound instead of sounding like someone is shaking a tin can full of bolts under the bonnet.
Stephen Strange

And how is the engine running? Excessive wear in the valve train, makes the cam seem like a mild one with power low down, but runs out as the revs become higher.
Not much use if you have a long trip coming up, but might be best set up as well as you can for the trip, then, a top end strip down? Mike
J.M. Doust

Thanks for all the comments.

Mike- I am driving from Denver CO to Reno NV for MG2011 about 1100 each way. Will put on about 800 while there. It is the ALL Register every five year event. I did go to the last all register event in 2006 in Gatlinburg TN. There are usually right around 1000 MG's in attendance. I like your suggestions about different way to adjust the valve lash clearances. Also the sugestion about trying to put the lock nut under the rocker. I did change out the rocker assembly with the spare I had taken off a 1975 engine that I have disassembled for a rebuild. I also changed out the push rods from the same engine. I no longer have the problem with the lock nut only grabing a couple of threads. I went ahead and adjusted the lash, went through the process 2 times to double check. While the plugs were out I did compression checks also. The car does sound somewhat quieter now. I think it is just the normal chatter that the B series engine is known for. I don't think it is a warn cam as it does have good power through out the RPM range, maybe even better power at higher RPM's then the lower side.
Stephen- Thanks for your tips. I did not find any deep grooves on the rocker pads. I will check the rocker assembly shaft and if it is worn I will change out the parts and keep it around as a spare. After swapping out the parts today I took the car for a nice long ride and every thing feel good.I think I will survive the trip to Reno and back.

Twelve of my fellow club members will also be going on the trip.

Saftey Fast,
John Fraioli,
MG Car Club of England, Rocky Mountain Centre.


John Fraioli

John,
I'm green with envy... I would love to spend a few weeks driving the Rockies and the west coast in a MGB (must be better than the slow fat Sebring Auto I hired in Napa a few years back!).

Good luck with the trip and event. Let me know if there's a web page set up with some event info and pic's

MGmike
M McAndrew

What method are you using to position the valves before adjusting them? Rule of Nine? Both closed? I could never get repeatable measurements with Rule of Nine (i.e. adjust, turn the engine, recheck) even though that is more precise for positioning than both valves closed. Then I discovered that some valves at that point had the clearance still changing, it's maximum was one side or the other. I now adjust at the maximum clearance point, which means I can get repeatable measurements, and did make things a bit quieter to boot.
PaulH Solihull

While you are looking for points of wear mentioned above, and have a push rod disengaged,take a valve chest cover off and extract the tappet as well. Wear will be pretty obvious if it's bad. The case hardening will have been penetrated and the end will look "scarred", if this is the case the cam will most likely be damaged as well . When the cam and tappets are in reasonable order, the tappets revolve so the only acceptable appearance on the face of the tappet are very faint concentric circles, but dead smooth.
A little wear in all the components of the valve train can add up to a lot at the rocker/valve interface.
Allan Reeling

You are right Allan, and going back to Pauls' point, adjustment by rule of 9, can be tricky, I used a dial guage at last adjustment, so that I could get that'mid point valve closed' bit fiddly but it probably gave the most accurete adjustment. To be frank, there is wear in my system, but not disastrous. For road pretty good, for racing oh, might loose you a few seconds! Mike
J.M. Doust

I too had noisy tappets and always carefully adjusted when both valves closed at TDC based on distributor markings (have always done it this way) I tried the rule of 9 method from in reading the threads and it made a BIG difference - much quieter. I would suggest trying that method.
r. LEARY

John,

I had a VERY similar problems with a 1972 MGB some years ago. Kept adjusting valve lash and would be out of adjustment quickly thereafter. Just on one of rocker/valve train. I checked everything and ended up pulling the side covers to inspect the cam followers and cam. I was VERY surprised to see that one cam follower/lifter was wearing badly. As a result of the way the follower was wearing, it was not rotating properly when the cam came around which was making it wear even more rapidly. I inspected the cam to the best of my ability in situ and didn’t notice any significant wearing of the cam. I took a shot and put another lifter in that whole, and any other lifters that were showing bad pitting, while they were all out being inspected and put it all back together. I figured the worst that could happen would be that it would wear again which meant the engine might have to be pulled to change the cam. I knew the next 2 owners for several years but never heard of another problem with the engine going south or adjustment that could be made.

May be worth a look and try for you?!?!

HTH

Fred
Fred Wright

This thread was discussed between 29/05/2011 and 02/06/2011

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