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Triumph TR6 - Phew - that was close !!

After just replacing the defective 5 mnths old (Vicky Brit) 7/8" rear wheel cylinders with the original 3/4" SS sleeved ones that had served me so well for years, I took her out for a bit of a thrashing. Summer at an end, still lovely sunshine but somewhat cooler air which she loves (25C).

Going like a song with the resonant tune of the exhaust melodic in the air. Push her a bit, then a bit more - still going well. I regularly (albeit briefly) touch 6000 in 1st and 2nd and with the injection unit recently calibrated I figured go for it. 6500 in 1st, 6500 in second, backing of at 4000 in 3rd (hey this could be expensive!). Lets do it again - exhilarating.

Cruising speed hear a tinkle/rattle - ease off - more pronounced on over-run - blown a little hole in an exhaust gasket maybe?? - not worse under load - mainly audible on over-run. Not sounding good.
Nurse her home at idle to 2000.

hmm - definitely under the rocker cover - tic, tic, tic. Maybe a tappett locknut slightly loose - wishful thinking!

Cover off - holy sheet! - you know those top quality gold anodised alloy valve caps that look so pretty when the rocker cover is off - take a little advice - get rid of 'em ... and quick!

Mine were from SAH (Triumphtune) UK and were top shelf stuff.

The only thing that prevented an engine rebuild was that the cap that disintegrated did so at the outer edge where the top of the outer valve spring contacts the cap. The inner part of the cap was still held on by the collets and (just) bearing on the inner spring, stopping the valve falling into the combustion chamber. Phew!

I now have the peace of mind with good ol' steel caps. I'm still to put them on and clear the sump - hopefully the soft ally will not have got into too many sensitive bits (oil galleries) etc!

Roger H

Roger, That's a first class, oh my god, gee whiz , oh I'll never do it again , scare. The kind where a nice glass of vino and a gentle sigh of relief is all that's left. Everybody, let's toast to Roger's good fortune.
And hope there's some left for us too !
David Johnston

I heard of a nice trick on Sat. from a friend who was observing as I was (with considerable aid from Chris Trace) pulling the engine out.
Attach a small magnet to the oil filter to collect up all those little bits of "unwanted" stuff. I also thought that a magnet attached to the oil sump might be usefull. The filter one is probably better as it is easier and more often removed.

If I took my 6 up to 6500RPM, I would have extra frost plug holes in the block:)
Glad to hear little damage was done.
Rick C
Rick Crawford

Only one problem in Roger's case, those nice shiny anodized light weight alloy spring caps are not magnetic. On the plus side, they are reasonably soft and would be ground up if they got in the way (assuming not too big a chunk and specific location dependent).

Here's a "me, too" on the alloy retainers. In my case the valve collets were pulled/receded down into the softer retainer which raised the spring height. It got so bad that the retainers began to interfere with the roller rocker arms.

I found the problem when trying to adjust the valves after the car started to run funny - there was still tension on the rocker arms when the valve was supposed to be fully closed and at the adjust point. Used the rope trick to get those things offa there and put the steelies back on. That was about 8 years ago.

Brent B

Roger's and Brent's experiences suggest another thread...what not to do...!! Wonder how many other "lessons learned" there are which might help someone else avoid disaster?
Doug Baker

2 years ago I took a small magnet and using my grinder shaped it to the size of the oil plug..I then glued it to the oil drain plug and every oil change I just give 'er a wipe !
Charlie B.

Hey guys - still holding my breath!

As suggested, a magnetic sump plug is a very good idea. Anyone that doesn't have one should put it on the list. If you are lucky with the timing of an oil change, it can attract lots of little bits which can be tell-tales for something amiss before things get tragic. A while ago I found two small pieces of soft steel attracted to the plug. I couldn't recognise it at all. They were curved/sheared and each about the size of two match heads. After a 'virtual' rebuild with my TR mechanic, turned out it was part of the locking tab which, when bent up to secure the cam chain sprocket, had fatigued but not broken and finally came off. It had been crushed between the teeth and the chain and passed into the sump. It was only one corner of the tab, but it could have been worse and the bolts could have worked their way loose. Lesson? - don't re-use locking plates, tabs, split pins, copper washers etc - or anything designed for a once only use. There is a good reason for it.

SteveP - you are quite right (and BTW I love the qualification to the advice!)- still has me a bit sleepless though.

I was thinking of some sort of engine oil flush before re-starting but I've never done it as I reckon there are some pitfalls with the idea. It may be an interesting thread so I will start a separate one. All opinions would be greatly appreciated.

Roger H


I would recommend pulling the sump and rocker cover, then giving everything a good visual inspection. Look for any chunks and use lots of light. If you are satisfied that everything is OK after a thorough visual, odds are that things are indeed OK. BTW, I do have a magnetic sump plug.

One of the problems you run into with aluminum in some applications is that it has a low endurance limit. Adding insult to injury, many of the outfits that make these bits use something like 7075-T6 condition material. All they do is look at the static strength of the material and don't take any of the other properties into consideration. While 7075-T6 is rather strong for an aluminum, it is subject to stress corrosion cracking (think the big re-wing effort of a rather large USAF cargo plane in the late 70s/early 80s as an example). At work we will not allow the use of any 7xxx series alloys in a -T6 condition if the starting stock is thicker than .080". Similar stress corrosion cracking problems can occur in 2xxx series if they are not in a fully aged condition (i.e. a -T6 or -T81 vs a -T4 or -T3).

Thinking about the application, we have a narrow flange that is under constant tensile stress and a bending moment thrown in for good measure. Now we run the engine and the stress loading is increased in a cyclic manner. Here is where the lack of an endurance limit comes into play. If possible, get a good close up look at and some pictures of the failed surface. Odds are good that you will see a small polished area where failure initiated, then some striations that suddenly go into a rough surface where it went into overload and unzipped the rest of the way in catastrophic failure mode.

If anyone out there in hot rod land wants to lighten their valve train components, this is a place where you go titanium, not aluminum and especially not a 7xxx series in a -T6 condition or a 2xxx series that is not in a fully aged condition. While I have heard of aluminum rockers failing, it is not as common since the parts are beefier and as a consequence do not see as high a loading as the spring caps. It's that old P/A thing that I heard about somewhere working for you.

I too have a magnet on the drain plug. Went to the local plumbing store got a brass "plug" that has correct thread and just happens to have a convenient head on it that a standard socket fits. This plug has a hollow in it and I glued a magnet into this hole.

Steve, silly me. Magnet... alluminium.. yup do not go together. But the magnet is still a good idea though.
Rick Crawford

Or titanium retainers with a small steel insert to properly hold the collets. I'm not that familiar working with titanium, but the sharp edges of the collets kinda bother me....
Brent B

This thread was discussed between 14/03/2005 and 15/03/2005

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