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MG MGB Technical - Racing Rods

Does anyone know of of a cheaper alternative to Carillo connecting rods for the MGB engine.I had heard that there is a Chevy rod we can use ???? I am building up another motor for the old war horse, but don't want to totally spend the kids inheritance. Thanks ,Renton
R F Murray

Renton There is a local manufacture in Victoria Aus.
The name is Ridge Crest they have a web sight. I dont know what their prices are like as I have only bought solid copper head gaskets from them. Look them up.
Denis4

Saenz are cheaper.

Don't count the stock rods out unless you are doing up a really high compression high reving monster. The stock rods are pretty beefy (although also weighty, the reason people usually swap them out). If you aren't going above 7000 routinely, stock is probably OK.
Bill Spohn

Renton-
Arrow Precision drop-forged EN24 chromium-molybdenum alloy A-beam connecting rods are a bit cheaper and lighter than the Carrillo connecting rods (570 grams vs 588 grams), and much lighter than the OE items. However, Bill Spohn is right when he says that the OE connecting rods should not be counted out. The final connecting rod design (BMC Part # CAM 1588) used in the late 18V engines had no balance pads and were the lightest, weighing 760 grams, which is slightly in excess of 1/3 more than the Arrow Precision connecting rod. The most desirable connecting rods for any normally-aspirated street engine are also the lightest ones as, due to their reduced inertia, their reciprocation will not only produce less Primary Vibration and power loss, but also less stress is placed upon their big end bearings as well. These can commonly be found on engines whose identification numbers start with 18V-883-AE-L, 18V-884-AE-L, 18V-890-AE-L, 18V-891-AE-L, 18V-892-AE-L, or 18V-893-AE-L.
Steve S.

Thank you for that info.... I have so far not found any of the later rods,I normally would stay with the original rods,but my engine packed a sad, and one rod suffered, so I have to grind off the balance lump and polish and shot and match the balance of the other 3,so after market rods were looking like the way to go,except for the price. I have found though Harland Sharp roller rockers will save some money over the Moss Motors ones,I hope they are good uns. Renton Murray
R F Murray

Steve,

No primary vibration from reciprocating rods in a four pot - they cancel out - providing that they are the same weight of course!

Neil
Neil

Neil-
Almost, but not quite so. Primary vibration includes all of the forces that occur at the same frequency as the rotation of the crankshaft. This includes cycles of acceleration and deceleration of the rotational speed of the crankshaft. Lighter connecting rods require less energy from the rotating assembly in order to change direction. This being the case, they decrease the amplitude of this primary frequency, and thus reduce primary vibration.
Steve S.

If there was no vibration you wouldn't need the harmonic balancer pulley I guess?

Simon
Simon Jansen

Balancing rods is generally considered as part of secondary balance rather than primary.

The rod motion can be separated into reciprocating and rotational elements and the rotational element is considered as part of the primary crank balance. Weight isn't really the issue here and is minor compared with the weight of the crank & flywheel. Weight is an issue in the reciprocating element together with the piston, which is purely reciprocating. The split between rotation & reciprocation depends on the design of the rod and I don't think the Carillo or other special rods are actually that much lower in reciprocating mass than the very late 18V rods.

Chris at Octarine Services

I have a set from maxspeeding@gmail.com They look the business tho I have not yet run the 1950 engine they were purchased for. Much lighter than standard and claimed to be balanced to 1 gram. On ebay under conrods or email them direct. They are very helpfull and the price was excellent. I know they are chinese but at the price I felt they were worth a try. Jim
jim soutar

Jim, I don't think I could bring myself to trust Chinese rods no matter how inexpensive. They might look to be definitely expensive if they let go on you!

We balance within 1 gm. for street and 1/10 gm for the track (excessive on the street).

I like the late MGB rods. Even the heavier full floating straight cut as opposed to the early diagonal cut rods are good, although the press fit are even lighter and better.

I use the latter in my Twin Cam on the theory that what doesn't have circlips will never come adrift.
Bill Spohn

Give or take on rod weights

Carrillo/Pauter 580ish grams

Early angle MGB raod 960 grams

straight MGB floating rods 870 grams

18V straight rod press pin, artound 800 grams form memory.

So when you compare evne the lightest facotry rod to the aftermarket rods, you get over 100 grams, that a fair amount of weight, but as mentioned here, I wouldn't waste my money putting expensive aftermarket rods in a street engine, unless you have plenty, then enjoy :)
Hap Waldrop

Steve,

I don't think I agree. Vibration is caused by forces that change direction. There are no rotational forces, and there is no nett primary force as the individual forces cancel out - two pistons/rods are going up as two are going down. There is a balance issue - the primary forces will not cancel if the reciprocating masses are different - but the actual mass is completely irrelevant. No nett force = no vibration...?

There are secondary forces, which vary in proportion to the reciprocating mass. But the reciprocating mass includes the piston and piston and gudgeon pin, so the effect of reducing the reciprocating mass of the rod is much reduced. You will not get rid of the secondary forces, but at least you can make the forces similar in all cylinders (by balancing) which will make the engine run/feel 'smoother' ie less variation in vibration.

Neil
Neil

Thanks for all that guys, I've taken the leap and a set of the Cheaper rods..I paid 240 pounds, They certainly look the business and read well...lets hope they perform on my 1950.
R F Murray

Renton Good luck with your choice. That makes two of us taking the chance. Bill I respect your comments tho I find Chinese products can sometimes be very good as well as very bad. What better engine to experiment with than the "B" ? even if it does go bang they are cheap enough to rebuild/replace. If the Max rods do the job that their spec says they can do, I reckon Renton and I have a real bargain. My original rods needed new small end bushes and the big end resizing, therefore the new rods did not cost much more. It will be very interesting to see what actually happens. Here in England a set of Carillo"s cost almost as much as a complete standard engine rebuild. Let us all know of your experience with these rods Renton. Jim
jim soutar

It has just struck me of the irony of all this....MG's are now made in China....but of course being an old fart...I maintain if it didn't come out of Abingdon it isn't an MG anyway. Renton
R F Murray

Jim I hope you are right on these rods, I have just bought a set. Made an offer at £245 and got them! They certainly look the business.
Just had a major failure on my MGA race engine through rod failure, so need a set of steel rods for that as well!


CP
Colin Parkinson

I hope I"M right as well. Seems I"ve started a world wide interest. I hope we can all keep in touch and build a history of just what these rods will stand. The spec reads just the same as other 4340 rods offered, lets hope they deliver . Jim
jim soutar

Hi Colin

The engine sounded very good on the rollers, shame about the rod. What revs were you pulling?

Peter
peter burgess

Neil-
Equal opposing promary forces will cancel each other only if they are on the same plane. Except in the case of horizontally-opposed engines that make use of forked connecting rods, in a piston-driven Inline-4 engine the cylinders are offset, therefore there is a rocking force. Also, if equal-weighted connecting rod & piston assemblies did in fact cancel each other's secondary forces, there would be no need for counterweights on the crankshaft. If by "variation" you are refering to the amplitude, and not the frequency, of vibration, I must agree. That's the point that I've been making.
Steve S.

Peter, I have emailed you direct

Colin
Colin Parkinson

Jim, I agree that some Chinese products have proved to be quite decent. I just shy away from them because buying them is often like playing Russian roulette. Even if the last batch of a part were fine, the next batch may be crap.

Just ask all the guys with Chinese head studs - they would be the ones that end up in two pieces when you try to torque them to factory spec.....

I know that Chinese can often be the only game in town unless you are willing to hunt down and pay more for NOS. I pay more and wrench less. My choice.

Couldn't sleep at night wondering about Indian timing chain tensioners and Chinese rod bolts and wondering when they would self destruct.
Bill Spohn

Well I have got my rods from China. I do have to say they look the business.

But we will only know when we rev the engine to 7500!!

CP
Colin Parkinson

This thread was discussed between 04/05/2009 and 24/05/2009

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