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MG TD TF 1500 - TD new crank & engine rebuild?

Need a little help. I"m replacing the crank in my TD. What is the difference between a billet crank and a forged crank. Also it has been suggested to install a roller cam and lifters at this time. What are the advantages of this? Thanks in advance, John
John Hambleton

Well there are advantages to all of those, if new. MG's originally had a forged crank, both early and late. The later ones are better according to many. New billet is rock solid, bullit-proof. Roller cam and lifters will reduce wear and friction in the valve train and generally are much better than the antiquated original design if you want to drive alot and have a long lasting engine.

Brian W.
ZBMan

Agree with the above regarding cranks. Roller cams are a hit and miss item. In theory they give better performance and longevity, but in practice it depends on a lot of factors. I installed a roller cam kit in an engine with no other changes and saw zero improvement in power or torque. Even with no power increase it will last twice as long as a standard cam, but it also costs twice as much. It also requires very high spring pressures so there's the question of increased wear on the rockers and valves. If you're developing the engine all around then the roller may offer more power.
Steve Simmons

Your basic questioln does not seem to be answered.

Factory cranks were cast - molten metal poured into a mould is then machined to spec. 22528 is the earlier MOWOG crankshaft made of EN16, which contains only manganese and molybdenum; tha later 168557 is made of EN100, which is molybdenum, nickel and chrome steel. While the latter is better, the former can be fine for many miles if the proper radius is maintained on the journals. Most guessed are that a torsional vibration at about 4500 RPM weakens the metal, causing failure. When factory cranks break they do so without warning, usually at the #1 and/or #4 webs.

Modern steel cranks are made of 4340 Chrome Moly steel, far better than original.

Forged cranks are made by taking a piece of rolled steel and fortcing it between two dies, which is then machined. The steel is made under such pressure that it is therefore stronger; they do need to be heat-treated. Nodular iron cranks are also available.

The best and most expensive crankshafts are billet cranks - a solid piece of metal is machined down to the shape and dimensions of a crankshaft - sort of like the sculptor who starts with a large block of marble and removes everything that does not look like a nude...

There are some very good basic new cast cranks out there made of much improved materials, and are excellent for anything short of racing situations. I am considering stocking these cranks for sale.

A number of people also sell forged cranks, and custom makers make and sell billet cranks, usually on demand. Moldex (US), Phoenix (UK) and Auscrank are all known makers of various different quality cranks - all far better than original.

I hope this answers your questions?

Tom Lange
MGT Repair
t lange

Tom,
Can you from your experience explain the symptoms of a cracked crank? My mate's TD has a strange noise we are trying to locate? We thought it was the timing chain but that was not the case. He says it is only running on three cylinders although the colortune shows it sparking. No. 3 seems to be the problem although the compression seemed good. You can pull no. 3 plug lead and nothing changes. Perhaps a hairline crack? It only seems to appear under load and I doubt if it is a carb or fuel problem. We have tested everything we can think of.

Regards
Declan
Declan Burns

Declan - I have never broken a crank, so I cannot give you first-hand comments. From anecdotally what I have read if you are driving at speed, the engine can grenade. But the main symptom is a persistent knocking at low RPMs, say up to 2500.

Without knowing what the sound of your mate's engine is, I can't suggest anything further. I believe LaVerne has some expereience with a broken crank, and may be in a better position to help..

I would start a new thread to get the largest response.

Tom Lange
MGT Repair
t lange

Thanks everyone, that’s pretty much what I thought.
Tom I’ll be calling you later today.
Delcan when this happened I was driving at speed and pulled off at an exit. The exit is downhill so I braked without much success then downshifted. That’s when the noise from the engine first started. I immediately cut the engine off & called a tow truck. I had never heard this sound, but knew it was not good. Had the oil pan removed and found the crank broken into at the first piston. The sound it made was like something lite hitting the oil pan from inside. It wasn’t loud or heavy like you would expect from a thrown rod hitting the sides of the block. My thoughts now is it was the two ends of the crank rubbing/grinding against each other. I won’t know for sure until the machine shop gives me the results. I’ll post the results. Hope this helps and you never hear this sound, John
John Hambleton

I suddently heard a deep knock, and thought it was the car passing me. The oil pressure gauge dropped to near zero, and I turned it off. I could wiggle the crank pully a little. Break between first main and rod. George
George Butz III

The crank in a club member's TD broke at the #1 piston while he was driving the car. He said that something "didn't sound right." He immediately turned off the ignition and had the car towed home. No damage was done to the engine.

Stains at the break may indicate that it had been cracked for a long time (??)

Lonnie
TF7211

Here is a pic:

LM Cook

Declan,
check both carbs are actually opening, the clamps sometimes slack off. They will run OK but won't take load.
Tom,
a local owner had a crank go at 4000rpm, we salvaged the water pump, oil pump, flywheel, carbs, dizzy and cylinder head, nothing else.
We think the first break was number 1 web as the rest ended up on the motorway.
He is still on the road 30 years later with a fully balanced, crack tested crank.
Ray TF 2884
Ray Lee

I have a crank here from a friend's car which broke at #4 and the car was jumping and banging around like it had rocks in it. Terrifying sound.

A misfire on #3 is unlikely to have anything to do with a broken crank. If it's only under load, regardless of RPM, then you can rule out electrical issues. Check that your carbs are both functioning properly and aren't clogged with debris. Also not a bad idea to do a compression and/or leak down test if nothing else stands out.
Steve Simmons

I too have experience with a broken cvrank - purly my own fault.

When I was 19, I decided to rebuild my TD engine. Don't ask me why, It really didn't need it. I just thought it sounded cool.

Up to that point, I had always thought of myself as a mechanical genius.

Didn't realise I had installed the centre main cap backwards. Thought it strange that I was having trouble turning the crank, but W.T.H, nothing to worry about. Finished assembly and started the engine. Wow, I'm still a genius!

That lasted 15 minutes when suddenly it started to run really rough. Didn't take long to figure out the problem. On dismantling the engine, I felt really stooopid, but more importantly, humbled.

I realised that I am a mortal, just like everybody else.

Fortunately the dealer was a really good guy and felt sorry for me and sold me a new crank for $126. Still have the parts ... just a reminder that we can all make mistakes.

Gord Clark
Rockburn, Qué.
Gord Clark

My crank went about 2006, I installed a Moldex crank, with Venolia pistons and Crower Rods. been running 12 years now with no problem. Mine broke right behind the front bearing on number one. drove it 2 miles with the bronken crank, ran like crap. got to where I was going and shut it off and it was froze right there. no damage to the engine at all, Dave Zipp had a Moldex and i bought it. modern rods and pistons really make a difference.solid running engine and basically bullet proof. You will know when the crank breaks, it dont run real well.
TRM Maine

I was over at my mates place and we swopped over the dizzy. It made no difference so I would almost rule out an electrical issue but...read on. The car starts fine and ticks over very well but as the engine speed is increased it sounds and feels rough as if there was an imbalance somewhere which could very well be. One thing we did notice which is pretty strange. When idling and no 3 plug lead is pulled it appears to make no difference. If no. 1, 2 or 4 is pulled the speed drops off and you can feel it running on 3 cylinders. Installing a colortune on no. 3 shows it firing and all compressions are fine. Could it be a head gasket issue?

When the gearbox was repaired earlier in the year a new clutch was installed. He says it was centered as he used my clutch centering tool. Any thoughts on the rough running?


Regards
Declan
Declan Burns

Assuming the spark plug is firing, I think you'll find that a compression test will show low results on #3. Check for a blown head gasket or a leaking / stuck valve. A leak down test would also pinpoint any such issues.
Steve Simmons

Steve,
Compressions were ok that's why I think it is more than likely the head gasket or (hopefully not) a clutch imbalance issue. As far as I know he did a leak down test but will check and re-comfirm.

Thanks
Regards
Declan
Declan Burns

Well something is going on if you can remove #3's plug wire and nothing changes. With the plug firing, all I can think of is a major compression leak. Good luck and keep us posted!
Steve Simmons

I too went through a broken crankshaft. We had been driving on a two car tour. I had just minutes before remarked to Barbara, "Isn't the car running good". Just a few miles down the road came the knock. pulled over and neither of us could pin point the cause, but home we went on a flatbed wrecker.
I pulled the engine, and took it to a local machine shop. we could not detect anything, until we started to unbolt the main bearings. Removed the front one and it broke in two. Interesting to see the crack marks, that had started some time ago. The final break showed there was less than 1/8 inch of metal that was shiny, so it had been going on for some time.
I now have over 69,000 miles on TF 2302, I don't drive it hard but am no slouch when going through the gears.Cheers, Byron.
PS driving on the Indy track.
JB Warwick

Declan, colortune says nr 3 sparks but what you see is the colortune plug sparks. What about a new plug in nr 3
Huib Bruijstens

Huib,
All plugs are new and have been swopped around-same rough running.
Regards
Declan
Declan Burns

I had the same misfire problem on my TD.
Comp on no. 3 was only 15 psi lower than the rest but turned out to be a cracked piston ring.

After a rebuild, had a similar thing with No.3 not firing on idle. Mechanic had left inlet valve on no.3 with very little clearance.

Also, cyl 4 misfire where the lead had pulled off the back of the plug cap but wasn't noticeable under the rubber shroud. Checking with a meter from distributor rotor pickup through to plug cap showed open circuit and the spark was having to erratically jump 1/2 inch.
P Downing

This thread was discussed between 17/09/2018 and 02/10/2018

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