MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG TD TF 1500 - XPAG crankshafts

Hi All,
What is the consensus re the early cranks (TC/early TD 22528) compared to the later (TF/Wolseley 168557) cranks? I know the later ones were made of upgraded steel, but did this actually do much good in preventing breakage?

Has anyone done any research or taken data on the topic? I know of cars which are still running on the early cranks. Two, in particular which had VERY hard lives without breakage.

Back about 50 years, there was a theory floating around that the early, softer metal was less brittle and so less likely to break. Perhaps the later steel was introduced to reduce wear as much as preventing breakage? Do we make too much of a deal about using a later crank? An old expert in the 1960s told me it was more about having the steel at the right temperature when it was forged.

P.S. 22528 and 168557 are the numbers on cranks I have. I am aware that various writings list the later number as ending in 828 or other, instead of 557.

Bob Schapel

Bob Schapel

In about 1957, I bought an unwanted and unloved TD and immediately realized the main bearings needed to be changed. In reassembling the engine, through lack of experience, I remounted the centre main in reverse position and proceeded to break the crankshaft.

At this point I learned that the early TD cranks were made of nodular iron. The replacement crank I bought was cast steel. The TFs had a forged steel crankshaft. You can see the migration in quality.

New crankshafts are outrageously expensive; I believe the Phoenix crank to be in the $3500 range. You folks in Australia are lucky, because you can buy one for half that price from Auscranks.

Gord Clark
Rockburn, Qué.
Gord Clark

Thanks Gord.

That is interesting. I, too, have a few stories about issues I had due to inexperience! Most of us have been there. Now inexperience has been replaced by old age. I think I was OK somewhere in-between, but I can't remember!

Where did your crank break? What was the "reverse position" you mention? You might have done what I did to a rear bearing cap about 50 years ago. If you wish to communicate by email I am bobschapel at optusnet dot com dot au.

Forged steel is a good format. But I am pretty sure that all the XPAG/XPEG cranks were all forged. However, despite playing with TCs for half a century, I am still learning (and forgetting).

I have never used Auscranks, but if they are good, surely they can be ordered worldwide? If not, let me know and I could buy and send on, for a small fee (He he he).

Cheers from South Australia,
Bob Schapel
Bob Schapel

I just goggled Auscrank and it came up as Crankshaft Rebuilders. Unfortunately they have just closed down.No longer in business.
R E J Stewart

I,had the cracks in my crank repaired when the engine was done at the local engine builde. I was lucky that there was a century of knowledge at the shop, and the builder knew about the XPAG.

It is not so much about the metal of the crank but the way the journals were originally ground. They originally were not cut with a radius at the edges and caused a weak spot, where they cracked.

Mine had the cracks ground out , re-welded, then machined with a radius. Must have been ok, cause 11 years later the engine is still running fine.

CR
CR Tyrell

Bob,

My crank broke (completely) at the centre main, where I had foolishly replaced the centre main backwards, which was (and still is, I assume) possible to do.

I still have the two pieces and have been threatening for years, to mount the rear portion on a finished piece of wood, and award it to someone in our club, as a 'hard luck' trophy.

Gord Clark
Rockburn, Qué
Gord Clark

I believe XPEG cranks were Nitrided which is a surface hardening, and were not to be reground. However many airplane cranks are nitrided and are reground and renitrided. If I had a XPEG crank that needed reground I would send it to an aircraft grinder. These engines were I believe built by the same company that built engines for Massey Furguson and Ford tractors. In pictures they look the same for a fraction of the cost. Be interesting to check out
DL Rezin

Interesting stuff!
CR, That is fascinating. We all assume that a cracked crank is throw-away, but your story supports the idea that they can be repaired. The main problem is that very few people are skilled enough to do that sort of welding. I once ground a shallow crack out of a crank and it survived another 23 Race Meetings. Luckily the crack was not deep enough to need welding. I only replaced that crank when it cracked at the OTHER end due to a loose S/C drive. I thoroughly agree with your radius theory. I always re-shape #1&4 crank radii with a small grinding tool when I build an engine. See diagram and photo.

Gord, That is an interesting story. I guess the crank had weird stresses to cause that.

DL, I had heard about the XPEG nitriding. It would be great to resist wear. My concern would be that it is very hard and so might be brittle and possibly crack more easily. Maybe great on a rigid crank but T-Type cranks flex. I am not an engineer, but your point is a good topic to ask an engineer/metallurgist. I remember back in the 1970s, TF 1500s had a reputation for broken cranks. Of course that was only rumours.

REJ, That is a pity. A friend recently had a crank made (by a local machinist I believe) for his TC special. I will ask him who did it and its cost.

Bob





Bob Schapel

So are there any driving tips that might prevent or postpone a cracked crank?

John Quilter (TD8986)

Is there a "critical" RPM where the XPAG crank harmonics cause a problem? Maybe labouring is as bad as revving it?

That is a very good point John. I know that some cranks have "critical" points in the rev range where they do have problems. I think that was about 4200 RPM in our early Australian Holden cars. They could be held below or above those revs, but harmonics played dirty tricks if held AT those revs.

My road TC always cruised very happily for long periods at 4200 RPM. So if there is a problem RPM for the XPAG, I assume it must be well above that. I have heard very little about critical RPM in relation to our engines. Hopefully it is well above the rev range we use.

Has anyone else heard of critical RPM in XPAGs?

Bob


Bob Schapel

I think most modern drivers of XPAG /XPEGs get nervous about rpm usage and want to operated them like a modern car. There has been much discussion regarding the harmonics effect on XPAG crankshafts. These engines were designed to run at sustained high rpm’s in the 5000 rpm range. It’s when these little engines are lugged down or when the inherent harmonics come into play that failures occur. These harmonics tend to appear in the 3000-3500 rpm range and sustained operation in this rpm range is most detrimental when considering the cause of crankshaft failures.

As stated in another post above, it is also imperative that a proper radius on the journals is maintained when the cranks are reground. Poor attention to machining is contributing factor. Though some crankshaft failures do seem to occur it probably is far less frequent than say the 50’s and 60’s due to poor performance of the early crankshafts. For the most part it seems that crank failures due to poor metallurgy related issues have since been culled out over time and breakage. But of course so many of these cars have been laid up for decades that some marginal crankshafts are still out there.

It is important to have a crankshaft’s integrity checked through mag testing prior to refurbishment. Any modular iron or steel crankshaft that doesn’t have a consistent sounding, distinct and sustained ring when the counterweights are tapped with a mallet should be deemed suspect and be discarded. The later cranks or billet offerings from various manufacturers being the referred replacements. Phoenix, Moldex (USA) and there is at least one other USA manufacture whose name escapes me at the moment are manufacturers that I’m aware of. I’m sure there are many others worldwide that have offerings available. Manley Ford also has a rather unique crankshaft design and offers stroker kits.

I’m personally not a big fan of nitriding crankshafts. As an anecdote , back in the late ‘70s or early ‘80s our local world renown racing machine shop purchased a nitriding machine to expand their shop services. A friend of mine offered up his new crankshaft from an Arias Top Fuel “Hemi” Rat motor as a mule. Well the operator left the crank shaft in the process too long. But while most everyone was giving high fives, the shop owner walked up to crankshaft with a mallet and smacked the counterweights. The crankshaft shattered. Nitriding has its place but if not done correctly then, it too can be detrimental into itself.
W A Chasser

Historically, the harmonic issue occurs at around 4200-4400 RPM. However with modern balancing practices, it seems these issues are behind us. I've put thousands of miles on my TC at those engine speeds without issue.

The real danger is lugging the engine. I heard a TF crank snap 100 yards ahead of me once. We had been telling the guy all day to stop climbing hills at 1800 RPM with his foot on the floor. He was convinced that revving over 2500 was bad for it.
Steve Simmons

This thread was discussed between 26/02/2022 and 08/03/2022

MG TD TF 1500 index

This thread is from the archives. Join the live MG TD TF 1500 BBS now