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MG TD TF 1500 - Changing Rear End / Breaking Rods/Replacement Rods

I have had trouble with the engine not standing up to 60-70 mph speeds with the 4.3. Since putting the 4.3 rear end in the car I have busted the crank, installed one of the new hardened ones from Moss, no problems with this since.. Rod through the block 2 years ago, ouch !! Last Sunday had another rod give way :( This car has a lot left @ 60-70 mph and will run tops about 80 mph. Has not run at this top speed for any extended time !!! I had been cruising on the interstate 60-70 mph both times when it give way... What does anyone know about different rods ??? Talked with "Carrillo" about their rods, 16 week wait.... Does anyone else have any experience with after market rods for the TD ??? Any suggestions or advice on beefing this up would be appreciated .. What speeds does everyone else seem to be able to travel with the 4.3 rear end ?? Has anyone else had trouble with this ???

Thanks, John
John Kinney Danville IL JVK52TD@AOL.COM

Is it the rods that are breaking or the rod bolts? It's somewhat unusual for the rod per se to fail. I assume you're not re-using rod bolts, tightening them properly, etc.

I've been pleased with Carillo-style rods made by Gordon Allen in England; the wait was outrageous, but the price was not. These rods, like most Carillo types, are fairly heavy. I'd like them even better in titanium.

I had some Crower rods made for a non-MG motor and was pleased with them also. Crower just dials in the parameters and lets the CNC machines do the work; the end result is an I-beam rod rather than the H-beam Carillo profile. I think I paid about $150 per rod. The wait at Crower fluctuates depending on the racing season. You can consult with them about the weight; they've got a couple different weight styles. Titanium is available for about twice the cost of steel.

Cunningham in Los Angeles also makes what I've heard are very good rods. And they're probably the only rod maker who will do a pinch bolt on the little end--although I wouldn't go out of my way to get pinch bolts.

That does raise the question of pin retention. Full floating has certain advantages, especially in engines which are disassembled frequently. But you would have to rework the pistons for the retainers, and I would not use the notched stock pins in a floating application. Pressed-in pins have a lot going for a street motor.

Aren't new forgings available from the usual suppliers? I know custom billet rods are pretty, but forgings have inherent grain structure advantages over billets--especially if the forgings are well made using the right material. At least part of the advantage of billet rods lies in quality control and really good bolts.

What ever rods you decide to use, choose good bolts. I've been disappointed by some of the bolts I've gotten from T-series parts houses. Especially supposedly super duty bolts where half the head had been removed by hand grinding and the operator nicked the shank. I have found ARP to be very helpful in supplying custom rod bolts, although I haven't tried to get bolts for stock T-series rods from them.

Finally, I wonder if it's the 4.3 rear end that's causing your rod problems, for a couple reasons: 1) From what I've heard, this isn't a common complaint from the 4.3 crowd. 2) Although the rod is having to push harder against the crank with a higher rear end, the greatest stress on con rods is RPM. The worst moment is the end of the exhaust stroke when there isn't a gas cushion above the piston and the rod changes direction; the piston wants to keep going through the head and the rod's got to pull it back. These forces increase with the square of the RPM. Anyway, RPM is reduced with the higher rear end.

Is it possible you just got a bad batch of bolts? Did you magnaflux the rods before installing them? Check the big end for round?
Jack Williamson

In addition to what Jack Willimson has written, I'd like to
add the following (learned at the school of hard knocks).
I, too, threw rods twice, once necesitating replacement of the
whole engine, the second time i got by with welding the block.
Both times the cause (as found out after the second tragady)
was the result of reusing the gudgeon pin pinch bolt and (worse
yet) over touquing them. I went by the torque value in the Woods
manual, which calls for 33 ftlbs on the pinch bolt. It finally
dawned on me that the same torque table was only calling for 27 ftlbs
on the big end bolts which are the same size bolt! That means that
the pinch bolts were over torqued by about 30%. I also found out,
by talking to a local expert, that the pinch bolts take a tremendous
load whenever one is decellerating, due to the vacuum developed
in the cylinder above the head (reason why it is recommended not
down shifting to slow down). Without knowing the history of my
problems, this local expert said that usually, in a four cylinder
engine, number one or number four rod pinch bolt will go in
situations like this. He hit it right on the head - my first
disaster was the number one rod and the second was the number 4!
David DuBois ddubois@sinclair.net

I have been following this thread with great interest. I
too have the MGA 4.3 gears, but going down an interstate
at 65-70 (with a lot left) in a TD with the firm
suspension bouncing around in a deafing 70 mph wind
would (for me) be a "religious experience."
Do others drive really their TD's like this? So much for my
leisurely Sunday drives on twisty roads or running
local errands to the store for bread and milk.
Joe Holtslag

Joe, until I moved to LA recently I used to drive my TD just like that. I commuted from San Francisco to Palo Alto on 280; if you didn't go at least 70 someone was going to run you over. I swapped out the 4.55 gears for 4.3's for this commute.

A few more connecting rod notes:

I recall reading comments in this group about using Unbrako (from SPS, Standard Pressed Steel company) socket head cap screws for the pinch bolt; I think the poster was from Au. I heartily concur with this practice; Unbrako socket heads are the best commercial / industrial fasteners (leaving aside aerospace exotica.) There's a nice fillet under the head, so it's important to use the proper washer. Probably lock washers should not be used; they do nothing for a correctly tightened bolt, and can fracture. Torque figures are available from SPS. Another advantage is that an allen screw is much easier to tighten than a hex head up under the piston.

I remember reading an article by, I think, Chip Old comparing failure rates of XPAG connecting rods and heavier XPEG rods. The author actually had some data; he wasn't just speculating. The upshot was that heavier XPEG rods were less reliable than the XPAG's. I don't think there was any discussion of the failure mode. Anyway, it makes you think--weight can stop a locomotive.

I guess if I was buying a set of rods I'd buy Crowers or similar high quality billet I-beams for several reasons: 1) Experience with the usual MG parts suppliers has made me skeptical about quality control. 2) Price of custom made steel rods is about the same as new stock-style forgings. 3)The custom rods will come with really good bolts, and you'll be able to have a sensible discussion with the maker about where the bolts came from, who made them and out of what, how much stretch they should be installed with, etc. 4) I-beams tend to be significantly lighter than Carillo-style H-beams; although admittedly both types have their passionate supporters. 5) No pinch bolt with the billet rods; if I wasn't going to race the engine and take it apart frequently, I'd have the rods made to take pressed pins. I would have a set of pins made without a pinch bolt notch. 6) The billets will have a big end cap locating device such as a hollow dowell. The stock rod
s use the bolts to both hold and position the caps; this subjects the bolts to bending forces.

If I was just going to drive the car once a year in a July 4th parade, I wouldn't worry about the rods. But driving the car 70 mph on the freeway, I'm happy knowing the billet rods are there. Besides, they're relatively cheap insurance. The rods cost $600, but if a rod breaks it could take out 1) the XPEG block, worth say $1000, the billet crank at $1500 or so, 3) if something hits the Laystall head--well that would cost more and 4) all the downtime and other costs of a rebuild.

Lastly, if I was contemplating replacing both crank and rods, I'd give serious consideration to making the crankpins and big ends to MGA dimensions. The bigger diameter would give more overlap with the mains, albeit at a cost of more surface feet per minute. Moldex will make a very nice nitrided billet crank for about the same price as a new forging.
Jack Williamson

All the talk about new rods, cranks, and the 4.3 rear ends and I did not see anything about what I think is the best thing you can do for your XPAG: BALANCE! BALANCE! BALANCE!
I regularly run my TF at over 4000 on the freeway and it still has plenty left. It is .080 over on the bore and .010 under on the rods and mains. The secret is to have the whole insides balanced, static and dynamic.
T-type Tom

All these comments are really good stuff, and especially the one about balancing.

I run a '52 TD, with a 4.3:1 rear end, a Shorrock supercharger, and as far as I know, both the rods and the crankshaft are the original. When I was rebuilding the motor, I had 10thou taken off the head, and had the rods carefully individually weighed, so that after small adjustments, the four were within 1/2 gram weight of each other. The flywheel was lightened by about 3 lbs, (I don't remember exactly) and the whole shebang was carefully balanced.

The result is an engine with excellent performance. Only last Sunday I attended a meeting which involved cruising with 2 MGBs on the Interstate for some 10 miles. I was able to keep up without apparent strain at up to app 78 m.p.h. I have to say it wasn't exactly a religious experience for me, and I don't know if my passenger had one, although the look of concentration on his face might have implied some sort of reverie. For me it was just a case of let her rip, hang on tight, and to hell with the pucker factor.

I limit engine revs in all gear to 5000, the blower being geared up app 1.1:1, so it is never close to 6000 r.p.m..

I swear by balancing, and ALWAYS recommend my clients have this done during any major engine work.

Geoff Love
Geoff Love

I make sure to run my 53 TD 2-3 times per week since I got it running evenly and well. The biggest problem was balancing the carbs. I am sure it could use additional tweaking.

I run it around the neighborhood then one one day usually take it on the freeway for 30 to 50 miles at 48-5200 rpm. So far no problems and it runs like a charm.

I am convinced these cars were built to run and we should run them and not treat them like weaklings.
That is why::::
SAFETY FAST

Michael Balahutrak
53 TD
Michael Balahutrak Houston PopeyMike@AOL.com

Soneone sent me the following which I pass on with no comment:

Two brothers from the back woods buy a truck load of watermelons at ten cents each and drive 800 miles up to the big city. After selling all of the melons at ten cents each
they note that they had not made any profit. A few hours of hard math and the solution to the problem is found, they buy a bigger truck.

What is often overlooked by the "reengineer" is the simple fact that "you get nothing for free". You can quote the Torque Curve, Horse Power Curve, and any of a dozen or more articles and studies, but in the end changing the gear ratio at anyplace along the drive train changes the amount of stress applied to the basic internal engine parts. That stress may go up or down if we rise or lower the gearing so that the engine turns over at a faster or slower rpm for a given load. The opinion that "The engine is turning over at a slower rpm therefore it is not stressing as much" is incorrect. It is true that Zero RPM means longer time between overhaul, but that is not what the engine or
car was designed for. On the other side of the equation is excessive rpm. Run these engines at 10000 RPM and you will not have to spent alot of time driving the car around
the back roads on cool summer evenings.


All that being said what is my suggestion to cure the broken crank and con rod problem?

Regear if you must, drive faster if you must, but always bare in mind that for each action there is a reaction. (and sometime it ain't what we wanted)
Rob

I'd like to weigh in on the side of balancing also; I think it's especially important in a 3-main, long stroke engine lacking a harmonic damper! Balancing is also very inexpensive; you get a lot for a little.

Balancing alone, however, doesn't necessarily mean the crank and rods won't let go. Neither does magnafluxing. Unfortunately these procedures won't un-fatigue old cranks and rods of unknown history--at least not in my experience in the school of hard (engine) knocks.

Noone has an infinite budget, so trade-offs have to be made. If I was doing a rebuild and planning on driving the car hard, I'd sell my usable crank and rods to someone building a show car and put the proceeds into a really good crank and rod set. I think a rebuildable crank could fetch $500 (depending on number of regrinds) and the rods $25 apiece. The good stuff will cost about $1500 for the crank and $600 for the rods, less the proceeds from the original parts for a total of, say, $1500. And then you should subtract the cost of not magnafluxing / regrinding the original crank, not magnafluxing / resizing and straightening the rods and not replacing the rod and pinch bolts; that's got be another couple hundred. It still ends up being quite a bite, but so's blowing up the motor.

I know there are a lot of people driving the heck out of their XPAG/XPEG's on the original crank ground thirty under, etc. But there's also a lot of people who've been dismayed to find the crank broke just aft of main number one. You pays yer money and takes yer chances.
Jack Williamson

I just put a 4:55 rear end in my 51TD and have run it up to 70MPH. Religous experience it is.. But lots of fun. I think that driving them hard is what they are for. I have not really had mine topped out yet.
ThomasMaine@compuserve.com

As an addition to this thread you may want to review this article from the July 1952 Autocar.
http://www.el-dorado.ca.us/~ccouper/mgtd/mgtd_performing_midgets.htm
It mentions the need to pay attention the the Mean Max Road speed per Engine Horsepower.
There is a graph also to help you figure gear ratios per horse power etc. It is done on stages
of tuning but you could figure it out on HP or whatever.

Chris
Chris Couper

This thread was discussed between 28/08/1999 and 06/09/1999

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