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MG TD TF 1500 - XPEG head gasket

I have been helping a friend renew valve springs and seals (head still on car). We held the valves in place with air pressure. All went well with cylinders 1 & 4. When we did 2 & 3 air leaked from 2 into 1 and 3 into 4. This points to a gasket leak between cylinders but why only one way and not the other?
Anybody any suggestions? the head has to come off anyway but just out of interest.
BY the way, if you use this method take off the rad cap on TF's if there is a leak into the water space your radiator is toast.
Ray TF 2884
Ray Lee

Ray,

How did you determine air was leaking from 2 to 1 and 3 to 4? I'd be more apt to believe valves weren't seating than gasket leaking between cylinders.

Also, while removing the radiator cap is probably good practice, wouldn't the pressure have released and the excess go out the overflow?

Just thoughts, fairly early in the morning and I haven't had my coffee.

Gene
Gene Gillam

Gene,
we could hear the air escaping and a thumb in the plughole proved where it was coming from.
With all valves shut (rocker gear removed) the only way I can see air going from one cylinder to another is via the head gasket.
It did not reduce on opening the throttles so it was not tracking through the inlet valves. The exhaust valves are open to atmosphere so it was not going that way either.
If we had done it the old fashioned way (a length of pyjama cord down the plug hole) we would never have known.
As to removing the rad cap, the blow off would not be able to handle the water mass before the rad burst.
Got me fooled but we will find out next week when we lift the head.
Ray
Ray Lee

Of course you checked the compression at each plug hole. Rings are good?


M Grogan

What was the position of the pistons?

If a piston was at TDC, the the other pair would be at BDC. The difference in volume could explain the one way leak (but only barely....??).

On the attached picture you can see what I mean. To get the effect you had, I'd expect the 2 and 3 cylinders to be at TDC?

Willem van der Veer

Compression tested at 150/160 psi starter motor and throttles wide open.
With the air method always at TDC it is not funny if a valve drops into the cylinder if the air fails.
Also remember, in gear hand, brake on or the car will run over your foot :-)
Ray
Ray Lee

It'll be interesting to see what that gasket looks like
William Revit


cylinders 1 & 4 absolutely no leakage past rings into crankcase,2 & 3 we could not tell because of leakage to 1 & 4 but I suspect the same.
This engine was still hot when we did this, so it was tested under working conditions.
We will find out at about 12:30 UK time on Monday.
I will post info and photos when it is done.

By the way what is the original head thickness for an XPEG?
Ray TF 2884
Ray Lee

3.022" is, I believe, the stock thickness for both the XPAG and XPEG heads.

Tom Lange
MGT Repair
t lange

thanks Tom.
Ray Lee

The cylinder head nuts on this engine have plain washers under them. Is there any good reason for this.
Ray
Ray Lee

They didn't originally, and should not - there are only two times when washers are appropriate. 1) The head has been skimmed so often that you run out of threads on the head studs, or 2) with an aluminium Laystall-Lucas head. Then the washers MUST be special parallel-ground hardened washers.

If you look at http://mgtrepair.net/Head.html
you will see my high-quality head studs, that have an extra 1/4" of thread, to accommodate heads that have been skimmed excessively.


Tom Lange
MGT Repair
t lange

thanks again Tom.
I just want to make sure everything is correct on this engine. There are not very many XPEG's in the UK.
Ray
Ray Lee

@ Tom Lange
Could you elaborate on your strong aversion to washers under the head nuts. My aircraft/auto industry experience has regarded the tightening of nuts down onto a machined surface as bad practice, causing erratic tightening torques and damage to the surface under the nut. Why do Tseries cylinder head nuts have to be installed without washers?
Thanks in advance for the explanation.
T W Moore

TW - of course. First of all, MG did not use washers on their cars presumably because washers were not considered critical to the clamping force on the head gasket. Even new heads were not perfectly parallel, but the degree of misalignment was minimal, and not critical because of the fairly low stock compression ratio. Obvious as it sounds, we must remember that the head studs fitted were NEW when they were installed, with no weaknesses, no stretched treads, and no distorted nuts. This is NOT the case today, when our engines have been disassembled and rebuilt so often that the physical and structural characteristics of original head studs have been completely altered by repeated removal and replacement, and re-torquing of the studs and nuts.


When washers are appropriate is when the head has been skimmed a number of times and the head studs are close to running out of threads. The factory head stud has cut threads, and the area closest to where the threads end is often distorted or incompletely cut, so when a head had been skimmed multiple times (or the CR had been significantly increased), the nut would be forced onto an area of the stud that was not designed or manufactured to exacting specifications. When tightened, the nut wold therefore yield imperfect torque settings, which may well result in blown head gaskets. In this case, the proper washers would elevate the nut to clamp onto clear threads, which removes the problem.

When a head was skimmed to a certain degree, the factory DID recommend the use of washers: AKD 834, Section R, MKII : Engine .. Flat washers - cylinder head nuts, Qty 10, Part No. AJJ605, Fin. at engine 17028. The Special Tuning booklet notes: "Use 1/8" thick by 3/4" O.D. washers under cylinder head nuts (to correct reduced thickness)." Note that the engine has been modified to increase the CR by skimming the head to a greater or lesser degree, often for facing purposes.

This is why my ARP studs have improved on the design of factory head studs by A) having rolled threads that are not distorted by the thread ends, and B) have an added quarter of an inch of threads, so that thinner heads will not run out of threads, and have more than enough threads to ensure consistent torque. Also, head studs can have their threads distorted by double-nutting to remove or install them, and most head studs I have seen have been removed/installed with pliers or a pipe wrench. The shafts of the studs show clear evidence of having been forceably removed, which has distorted and weakened the stud itself. This is why I have C) had my ARP studs manufactured with an internal hex on the upper end, which is used to install the stud without affecting or damaging the shank of the stud in any way. And D), my studs are a far better grade of steel than the factory studs, heat-treated and manufactured to a far higher standard of quality. There is simply no better stud available, which is why racers install these studs in their engines (Thank you, Manley Ford).

I have indeed taken apart engines where flat washers have been placed under the head studs to correct some perceived situation, but they have been standard, hardware-store washers. They were gouged, bent and distorted by NORMAL installation by tightening to the factory torque spec, and there is absolutely NO way they would have improved the clamping of the head gasket - in fact, the opposite is true - the likelihood of a blown head gasket is significantly increased. The proper washers MUST be high-quality washers designed for this purpose, parallel-ground and hardened. Hardware store washers are none of these.

The only other circumstance is when a Laystall Lucas aluminum head is fitted, and the factory nut will obviously dig into the softer head, and gouge the mating surface. Again, the proper nut must be parallel ground and hardened (I do have a small supply of these, when needed).

Please see http://mgtrepair.net/Head.html
for a description of my head studs.

Tom Lange
MGT Repair
t lange

Sorry - for "facing" in the third paragraph above, please read "racing".

Tom Lange
MGT Repair
t lange

I should also add that while one might think that replacing just the studs with my super-studs would be adequate, distortion of the nut is often overlooked. These nuts have been tightened and loosened dozens of times over the years, and the internal threads are no longer true. ANY thread weakness of the stud or nut will result in imperfect torque, and can easily result in head gasket problems.

Probably a dozen people have written to me that they have repeatedly blown head gaskets and cannot figure out why, and I suggest that replacing the studs and nuts is their best answer. Not a single blown headgasket has occurred when my studs and nuts are used (to my knowledge).

Tom Lange
MGT Repair
t lange

@Tom Lange
Thanks for your prompt reasoned response.
T W Moore

One last typo correction to the last sentence of the last text paragraph - for "nut" read "washer." My apologies.

I must point out that I am not just shilling my own products, but trying to explain one reason why head gaskets blow when both head and block have been properly re-surfaced. That being said, I am inordinately proud of the quality of the head studs I sell, and guarantee them absolutely.

Tom Lange
MGT Repair
t lange

Thanks Tom. Every time I read one of your posts I get a little bit smarter.
MAndrus

Tom L.,

I enjoyed your as per usual excellent explanation of the head studs, nuts
washers on T type Cylinder Heads/Motors. Brilliant!

Cheers
Rob Grantham
TF3719("Aramis"),TF9177("Athos").
Rob Grantham

Running again.
It was simply blows between 1/2 & 3/4, the head nuts came loose too easy, we think it had not been torqued and re-torqued correctly. Can't account for the blow-by test going one way and not the other though. The head and block were checked for flatness both ways and found to be OK.The head was fitted without the washers which were ordinary stock. Head had been milled to 2.983" maybe why washers fitted.
We now have another problem, while jiggling the tappet cover remove the head we saw the dizzy move. The ally case is extremely loose on the iron core, enough to wear down the rotor and cap pickups, metal dust everywhere!. The owner is going to fit a new Moss electronic replacement.
Ray TF 2884
Ray Lee

As my history of posts will show, I am a firm believer in frequent re-torquing after initial assembly. (Some would say to excess.) I recommend re-torquing cold engines, after the initial start-up, after the first drive, after 100 and 500 miles, and I have been known to do it at 1,000 miles as well. This extensive procedure guarantees that the head gasket will be fully and evenly pulled down, and that all stresses will be as equalized as possible.

On initial assembly I lightly oil the stud threads and the bottom of the nut where it contacts the head, using the same motor oil I will be using in the engine. When I re-torque I loosen the first nut 1/2 turn and re-torque it to full torque, go onto the second, etc. Using a 19/32" short socket enables me to re-torque a head without removing the rocker gear (on the two ends the clips and springs must be removed, but that is the work of but a moment).

The distributor problem you mention is fairly common, and contributes a great deal towards rough running due to inconsistent timing. Sometimes the body and tube can be pinned together with grub screws, but often the joint is too far gone - especially in a TF it is very hard to see. It's often easier to find a replacement distributor. I've tried flowing different adhesives into the joint, but it has not worked so far.

Tom Lange
MGT Repair
t lange

Tom. Many thanks for your advice to Ray Lee about washers under head studs and other comments, actually on my XPEG engine. As he said we reassembled without washers as you advised. I will torque down after 100 miles and again at 500 miles as you recommended (about one month of driving). Next time the head has to come off I will also add new studs and nuts, although not sure about quality from usual UK suppliers.

Hopefully I have added a picture of the old cylinder head gasket in-situ before removal and replacement. If I fail, I'll send a picture to Ray for him to add to his posts.

Thanks again.
Neil.
N D Wallace

GASKET

Ray Lee

HEAD

This engine is +0.020" bored, no liner so very low mileage.
Ray

Ray Lee

I can happily vouch for Tom's ARP head studs and ARP nuts. While they do not appear as authentic as the stock hex nuts, they keep the head down so I can drive my car without worry. A very worthwhile compromise in my humble opinion.

Jack Long

This thread was discussed between 13/07/2017 and 19/07/2017

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