MGB MGB Rod Nut Question

[6T2TR4]

I have a question for the engine rebuild experts out there. This is my second engine that I have built and the first was over 10 years ago, so I am quite the rookie. My 79 MGB with the stock engine has the rod nuts that do not have locking tabs. Last night I was puting in the pistons and to make myself feel better I used locktight on the rod nuts but was not super careful about getting all the oil off the bolt end first. Now today I got that uneasy feeling that I should re-do this step while the engine is on the bench or just spend the extra $50 and buy new nuts. Am I making a big deal about nothing or should I redo this step? How do these nuts keep from backing off?

 

[vping]

Torque. I've built a few and am in the middle of three more. Never used loctite or locking tabs on any of them. Not on the two TD engines I just built either.

 

[BlueMax]

I Certainly hope you are replacing your rod bolts! The parting line is the weakest part of any engine; you need to protect this area at all cost. The rod bolt is holding everything together to prevent this area from failing. If you’re familiar with ARP bolts and would like a top quality bolt I would recommend ARP, It’s the best bang for the buck. This bolt will have to be altered slightly on the rod if your engine is an 18V. If you choose a standard bolt, that will work just fine for normal driving. Never use anything other than a light film of oil on the standard bolt. If you step up to the stronger bolt like the ARP they will provide their on lube. The lubricant adds in letting the nut have its least resistance whereby you get your most accurate torque. The ARP bolts will have to be pre stretch prier to their final torque. They have about 10 torque cycles before they need to be replaced.

 

[Hap Waldrop]

Yep, get rid of the loctite on the rod nuts. Follow Alan's advice get a set of ARP rod bolt and I would suggest having the big end of the rod resized with a rod bolt replacment. ARP rod bolts have 12 torque cycles which is probably twice the torque cycle of the stock rod bolts. Follow ARP instruction sheet and you will be fine.

FWIW lock tabs are a joke in almost all the locations they used them on these engines, I don't use any lock tabs in my engine rebuilds for obvious reasons.

 

[Brinkerhoff]

I agree, go to ARPs website, You'll never not replace rod bolts again. Kevin

 

[Hap Waldrop]

The part number is 206-6002, I order them all the time. I will mention this though, look at the stock 18V MGB rod bolts they aer chamfered on both edges of the bolt head, this is so you could never install them wrong, the chamfer is there to clear the camshaft, the ARP 206-6002 rod bolts were also used for another application, I always heard a AMC engine, and they have no chamfer on them, we complined to ARP for years aobut this to no avial, so what I do is put the chamfer on one edge of one bolt head of each bolt on the cam side and that chamfer would be bolt head facing the camshaft, I just do this on a bench grinder, it doesn't take much of a chamfer for this, and some camshaft today don't even need it, but I rather do this and find out I didn't need to than the other way around. Oh and before someone ask, if grinding the chamfer hurts the bolt, no it does not, most of us professional builders have been doing this for decades with no issues. Hope this helps

 

[6T2TR4]

Thanks everyone for the great feedback. Now I am going to pop the pistons back out and replace the bolts. I don't want to always be thinking about my connecting rods during my planned long trips across the desert. Can I replace the bolts myself or do I need to take the connecting rods to a machine shop?

Thanks,
Paul

 

[vping]

Im contemplating this too after following up on this thread. seems like safe insurance after spending a few g's on my parts and machining.

 

[Hap Waldrop]

I'll also mention this, if you are replacing rod bolts, ARP or otherwise resizing the big end of the rod needs to be part of the procedure, you would never want to replace rod bolts and not resize your connecting rod big ends.
As for installing your won rod bolts, it's not a big deal that can be knocked in and out with a hammer and drift, it's not press fit by any means, but there is no reason for you to do this, as the machinist will need to cut the parting lines for the rod and cap for resizing and the rod bolts need to be done after grinding the installed and torqued for honing.

Oh and don't think for moment that used connecting rods doen't need resizing. I've seen every few examples of MG rods coming out of used engines not being out of spec, in short they will need resizing, and every engine I rebuild get this done in house, this also allow me to control the clearence on the rod journal, which directly control your oil pressure, even as little as extra .0005" too much clearnece could effect your oil pressure as much as 20 psi to the lower side of things, rod and main clearence is big deal, and rod clearence is the bigger of the two in importance, as it is at the end of the pressurized oil feed, and too much clearence will let the oil bleed off too quickly affecting oil pressure in bad way.

 

[Scott_Hower]

Hap-

As I understand it, to resize a rod bigend, the cap is removed from the rod and then both surfaces are machined flat. They are reassembled, torqued to spec then re-bored and honed/polished.

Approx cost for rod resizing? Does this normally include first checking them for bend and twist as well?

Also, did you get the head I sent?

--Scott

 

[Hap Waldrop]

Scott, yes you use a Sunnen cap grinder on the rod cap and rod, normally taking about .002" off to get them to clean up at the aprting line, de-burrthe edge, then install the new rod bolts, go thru the torque cycle, the rod housing bore size will nto be samller than normal after grinding, and you use the Sunnen rod hone for this, Sunnen makes honing mandrels for different size rods, i hae all the mandrels to do the MG and Triumph connecting rods. Then you hone them back to size, I also have the very best rod measuring gauge you can get, it cost me like $2K, it also a Sunnen parts, it measures down to the 1/10th of thousands of inch, which is exactly the game you are playing with crank journals and amin and rod housing bore sizes. Sizes the rod does tow thing in engine build, it get the rod's housing bore back rouan and back to spec., and thru the spec range you can use this t help set your bearing clearences.

I get $60.00-75.00 to size rods and install rod bolts, and for 120.00 total I resize and balance them, I do alot of connecting rods.

I'm sure it did, quite a few boxes came in the week, I just line them as when they arrived and normally don't open the box until I'm ready to do the job, don't want to confuse you guy's stuff.