Triumph TR3 drawing

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TR racing cranks

Note (I do not have a good place to store this data so for now it is here):  Speedi-Sleeve part number for the Fan Hub of a TR3 or 4 engine is #99174. It fits over the fan hub diameter that the seal rides on and creates a new smooth surface for the seal to rub against if the fan hub has a groove worn into it from the old seal. Installation tool and instructions are enclosed with the Speedi-Sleeve. The Chicago Rawhide Seal number is 17387 and it is supposed to be a double lip oil seal.

  Now for net info on TR racing cranks:

Dear FOTers

I've been researching crankshaft problems with 4 and 6 cylinder TR racing engines.

I'm trying to find out the most reputable 'racing' Triumph crankshaft manufacturers (and suppliers) on both sides of the pond in the hope of developing recommendations for the most effective and reliable crankshafts 'by experience'. My research obviously has to centre on a 'use within rev limits' and 'with the right damper' formula to give accurate guidelines and to be fair to manufacturers.- I would appreciate your recommendations on leading Stateside crankshaft people.

 Obviously the one single equation that will almost certainly ensure crank failure (sooner or later) is to over rev the engine above design recommendations. Whilst on the 'sooner or later' angle, however, I know of three TR3 full race engines with 'stock' but race prepared cranks that rev regularly to 6500 and over. One driver ALWAYS uses 7000 RPM and over. He's raced the same engine once a year at the Manx Classic for the last seven years (7 races) and other events with no problems (all three engines use crank dampers). Similarly Hardy Prentice in the States uses 7200 RPM with a stock nitrided crank.

My initial research over here has uncovered the fact that stock but race prepared 4 cyl cranks have given some quite incredible racing service. It must also be born in mind that many of the stock cranks used for racing have, more often than not, done many thousands of road miles before being converted to race units. - Rather like preparing an old age pensioner (like Bill Dentinger) to take part in the London marathon!!

 I know of special 4 and 6 cylinder Triumph cranks designed specially for racing with 'dummy mains,' and hollow pins with a half inch drilling through each. These cranks are lighter and more overall weight is moved nearer the centreline of the crank allowing a higher rev limit. They have been used for about five years with great success over here with 'recommended' rev limits of 7500 for 4 cyls and 7000 for 6 cyls (with dampers). These cranks are, of course, expensive but they're machined from solid billets (which takes about a week of man hours) in Nitroy EN 40B steel (used for F1 cranks).

 Best wishes
Paul Richardson


The TR-2 through TR-4 crank is made of a Manganese Steel alloy. The English alloy code is forged right on the crank. It is EN-16. The alloy can be looked up in the "Machinists Handbook"...The EN-16 alloy has enough good ingredients so that it benefits dramatically from being Nitride treated in an ammonia atmosphere. A properly prepared, nitrided, stock crank is good for 6800 rpm and 160 hp for a long time with light rods, pistons, and an aluminum flywheel with a diaphragm clutch. It does not need a damper on the front. It does need nice radiuses on all of the journals, a good balance, and nitriding is essential.

Greg Solow


 

TR6 crank

Amici-
Thank you for the enquiries - briefly, we suffered a major failure on a new steel crank after only 4 hrs track time, several years ago, and decided that something needed done. After some research, we found that there is a problematic 3rd harmonic torsional vibration on pretty much any inline 6-cylinder motor. The 6-cylinder Triumph motor is especially susceptible since the crank has hardly any overlap on the journals, hence is "floppy", for want of a better term. At 7200 rpm, the crank is twisting itself into a frenzy; the original elastomer damper cannot cope with the forces, so something has to give way. The first victim is the flywheel, normally as a result of an early downshift, leading to failure of the flywheel fasteners. So we go 8 bolts, dowels & so on. The flywheel then stays on. Then the rotor arm fails. Then the cam drive falls to bits in various ways - cam sprocket drops off with the snout of the cam, or, in extremis, the chain breaks - seen it , it's true!. The tensioner smashes, and even valve springs start to fail. I've seen one motor where the engine backplate decided to part company with the engine. OK - it's ad break time - my kit allows either original or billet cranks to rev through the critical rev point without risk of destruction. It's easy to fit, but the motor needs to go backward in the frame by around 10mm, and there's some adjustment of pulley offsets to do. If you're unlucky, you got a long drive shaft, which'll need shortening by a bit. Most are OK. Kit costs #525 - I will be able to reduce this to FOT if we get a few orders. Steel crank = $3000 minimum - I think it's worth it, due to lack of collateral damage...

Final puff- the TR-6 I drove at Mid-Ohio, which set fastest lap of the week (with a fat rusty old tub behind the wheel), has a standard, unlightened crank in it, wearing said kit. The telltale said 7*00.. Please e-mail or whatever - I already posted the flywheel bolt specs & so on a while back.
Jon Wood

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TR six cylinder cranks

Hi All...

Great topic.

I have a question though, and I suspect Mr. K can provide some insight.

Early TR6's use a different crank than the later ones, I have no idea what the cutover engine number was, but I suspect it was CC50000... at any rate, folks refer to this crank as a "long snout" unit. The question is, is a long snout crank inherently any better or worse for one of the mega RPM applications? Or does it matter?

I was told by a TR250 Autoxer named Jeff Janick that long snout cranks are better, and then subsequently realized that they are also made from "unobtainium" when I started to look for one. As luck would have it, at least one of these has become part of my "collection", and I figured it would be nice to know this info for the inevitable "phase two" motor that I'll probably be building in the next calendar year or so.

Wow. 8000 RPMs with a TR6 motor. Koool!

Bob Lang

 

As I remember there was no difference in materials between the early and late cranks but, the later parts are cross drilled on the rod throws and thus a much better part.. Nitride hardening the crank will give about a 50% increase in strength.

There is a little system to follow in doing this and if you actually intend to do this contact me and I'll fill you in on how I did (for years). If you are not going to spin the motor don't bother with the effort.

Kas Kastner

 

> In trying to increase the reliability of our GT6 engine, my partner
> came up with the idea of adding a fluid balancer to the front end of
> the crank to take some of the flex and vibration out of the crank.
> Has anybody done this? With what results? We used a balancer from a
> 5.0-liter Ford motor and it seems to make the whole motor run
> smoother, but we haven't got all that much time on the motor to tell
> if reliability is improved. This actually increases the rotating
> mass. Would lightening the flywheel make any sense in combination
> with the fluid dampener? Any opinions, well-reasoned and insightful or
> not, are welcome. John Lehman

 

The 2 litre engine was the most reliable engine we ever had. It was so good and the crank very very strong as it had lots of overlap. (The TR-6 should be so lucky) The rods were the weak point of the GT-6 engine after they put on the TR-6 cylinder head. The damper is probably a good thought but torsionals in that engine were never a major worry. We turned to 8000 and made over 180 bhp at 7700 on the standard (ho ho ho ) Stromberg carbs. Making the rotating mass lighter is almost ALWAYS a good idea.

Kas Kastner

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