2500 TC has the wrong head ?

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Clifford Pope
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Re: 2500 TC has the wrong head ?

#31 Post by Clifford Pope » Tue Aug 20, 2019 4:02 pm

I thought it was a well-known problem with the straight 6, and possibly other Triumph engines of the period.
This from a thread on the TR Register forum:

"From my experience its the front washer that does all the work and can fail with catastrophic (for the engine) results. The washers take the end thrust which generally only comes from depressing the clutch which has the effect of pushing the crank forward.
Hence the heavier the clutch cover spring, the more load the (front) thrust washer has to take. Some Borg and beck clutches from the 70's and 80's were a nightmare in this respect. My advice would be to remove the thrusts after gapping them and then add a set of standard washers. gap them again and if they are not within a reasonable tolerance, replace with oversize units.
Finally dont sit with the car in gear and the clutch depressed at traffic lights etc.
All Triumph engines of this era have the same weakness and 25 years ago I had a dolomite Sprint engine which had to be seen to be believed when it was stripped.... It had started to machine itself away. I learned that one the hard way ! :o
I should have known as the engine in my 5 had been modified with a white metalled phosphor bronze 'safety' within the crankcase / block. That piece of work had been done within the first 11 years of its life as I bought it in 1979."

Of course if the OP's engine has already been modified then this isn't the problem.

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Re: 2500 TC has the wrong head ?

#32 Post by Clifford Pope » Wed Aug 21, 2019 7:47 am

Jaguar.jpg
Jaguar XK apparently can have the same problems:

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Re: 2500 TC has the wrong head ?

#33 Post by tadge44 » Wed Aug 21, 2019 2:50 pm

Quote OK in normal road use but gives trouble when the engine is uprated.

There is an inference above that the Triumph engine has only a 180 degree thrust whereas, as previously mentioned, mine had two half moons giving 360 degrees. I cannot see that the axial thrust on the main bearing cap as well as the block face should make any difference to how the two half bearings perform. Surely the cap is not flexing ?

I am also puzzled by a reference to a front thrust bearing unless it was only intended to refer to Jaguar engines.

I have read of the external ball thrust modification elsewhere and it does rather seem to be an answer to an unasked question and well beyond the scope of most owners to adopt.(Thouigh obviously successful in that case)Properly installed and lubricated I would expect the Triumph bearings to last at least 50000 miles in "normal" use. As also mentioned above, sitting in traffic with the clutch pedal depressed for long periods is casual abuse but very common and will accelerate wear, obviously.
I was not aware that various clutch pressure plate assemblies for standard road cars can be sprung more stiffly than OE equipment.One to look out for.

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Re: 2500 TC has the wrong head ?

#34 Post by Alec » Thu Aug 22, 2019 2:23 pm

Hello Tadge,

it's not easy to determine what happens in a running engine when the cap bolts are stretched by the thrust from the con rod, but it is not good engineering paractice to load such a structure in a plane that it is not designed to resist. There is a very good reason the thrust is only fitted to the block, which is very rigid. The people designing engines are experienced and knowledgeable engineers. Certainly the range has been stretched from the original design with a near 100% increase in power from the early Standard engine.

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Re: 2500 TC has the wrong head ?

#35 Post by tadge44 » Fri Aug 30, 2019 3:35 pm

Alex, your reply makes perfect sense to me in the suggestion that loading the cap in the wrong plane is not good practice, but once again you infer that the Triumph engine only had a half moon thrust washer bearing against the block. I do not believe that this is correct and my engine has the two washers. Am I wrong ?

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Re: 2500 TC has the wrong head ?

#36 Post by Clifford Pope » Sat Aug 31, 2019 7:06 am

Then your engine must surely have already been modified, by someone such as:

https://www.revingtontr.com/engine-tran ... dification


Incidentally my 1947 Triumph Roadster 1800, which used the pre-war Standard 12/14 engine, had two thrust washers each side of the rear bearing, the ones in the cap having lugs to prevent the washers from spinning. This engine was also used in the Jaguar 1 1/2 litre.

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Re: 2500 TC has the wrong head ?

#37 Post by Alec » Sat Aug 31, 2019 12:35 pm

Hello Cliff,

not a cheap modification; keeping an eye on end float and rectification if and when required would be cheaper as it can be done with the engine still in the car.

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