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MG TD TF 1500 - rod bolts- big end

I have regular replacement rod bolts on the big end that I purchased from BPN. They included castle nuts. I would like to get opinions on whether or not to use cotters. The largest I could fit is 1/16 which is pretty flimsy. Is it safe to go without?
Mark Butler

Mark,
This doesn't answer your question directly, but I recently installed new bolts from Moss (part number 321-269) that must be torqued correctly but do not use cotters. Here's a Moss blurb for their bolts: "What we ended up with, is quite simply the best Connecting Rod Bolt and Nut Set available for the MG T-Series engine today." I hope they are right.
Joe
Joe Olson

On my last rebuild, I bought new big end bolts and nuts from ASL. The nuts were not castellated but rather, were Nylock.

I've always had problems with that; believing that the Nylon would extrude at engine temperatures.

However I'm told that even Formula 1 engines that run at 19,000 RPM (with a rev limiter, no less!) use them.

So I installed them after getting assurances from several sources, and of course, they were easy to torque.

I'm just very behind the times!

Gord Clark
Rockburn, Qué.
Gordon A Clark

Gord, I have no credentials for opinions on nuts and bolts but I am philosophically behind the times with you. Those F-1 engines may turn 19+K rpms but the engines are probably completely overhauled and reassembled between races. On our cars we are looking to rebuild the engine once and drive it turning only 1 - 7K rpms but for a real long time. Racing technology (which I am very fond of and thankful for) does not always translate 1 to 1 to street driving.

Jud
J K Chapin

And also, people don't realize that a Nylok nut can only be used ONCE. The locking action of the nylon insert is completely negated when the nut is removed, even once.

Joe - how easily did the bolts slide into the connecting rods? You should have to use hammer tapping, or sometimes more - they should be very snug to avoid the cap moving about on a too-small bolt. Modern connecting rods have a small collar on the bottom of the rod that aligns with a similar groove in the cap to prevent movement. If your bolts slipped right in with light finger pressure they are far too loose, and can lead to catastrophic engine failure without warning. Did you by chance mic the bolts before you installed them, or have a good machine shop check over the fit in your rods?

Tom Lange
MGT Repair
t lange

Mark,
FWIW I was recently in a similar position. I will show you three photos. The first is a very classic example of what NOT to do. This is what I found the first time I dropped the pan.
How do you pronounce DDDDDDDPO?

Mort 50 TD

This is what happened to the missing wire. I found it in the bottom of the pan.

Mort 50 TD

This is how I chose to put it all back together.
Mort


Best of Luck

Mort 50 TD

Tom,
Good questions. My machine shop did the installation, not me personally. I'll ask the next time I talk to them and if they remember I'll post their answer. I think it is a good shop. At least it came highly recommended and has done work for Moss Motors and this high end place here in Santa Barbara: http://www.winningmakes.com/ . My car isn't back on the road yet, but the engine runs like the proverbial Swiss watch.
Joe
Joe Olson

Mort, hard to tell for certain (especially by a non-mechanic) but it looks like you used locking (safety?) wires (properly installed to resist loosening) on the big ends of the piston rods and cotter pins on the main bearing caps. Any reason why you didn't use locking wires on the main bearing caps? Motion vs. non-motion comes to mind.

Hope I don't have to go there but if I do, I like the aircraft type safety wires.

Thanks.

Jud
J K Chapin

Jud,
The main bearing is what has the safety wires and the connecting rods have the cotter pins. I bought stainless safety wire and the neat pliers that twists it. Also watched a bunch of UTube videos for technique.

I just digested a lot of advice from the BBS and elsewhere and went this route.
Mort

Mort 50 TD

I see, it's the main caps nuts that have the safety wire and the piston rod caps have cotter pins - right? Thanks.

Jud
J K Chapin

The rod bolts have cotter pins because they can't rotate out, but the main studs need lock wire because they can come unscrewed if only cotters are used there.

I use aircraft-spec cotters, with the two legs opened up as tightly as possible so they are completely snug. I have found that the cotter pin ends can vibrate off if the cotters themselves are left even the slightest loose on the bolts.

Tom Lange
MGT Repair
t lange

Hi Mark
After comparing prices of Abingdon standard replacement bolts and Moss's offering, I went for the slightly more expensive Moss/ARP bolts for both the rod bearing bolts and for the nasty pinch bolt. Castellated nuts and cotter pins aren't very appealing even if they do work. ARP has a good reputation in the hot rod world: the Moss/ARP design uses non-locking nuts which are quite highly torqued after assembly with their proprietary thread lubricant (moly?). Most racing engines I've had experience with(MGB, Lotus Ford T/C,) had no mechanical locking devices on the bottom end fasteners.
Of course I haven't even run the engine yet, so can't say it all works.
T W Moore

Jud,

For the record and by the rules, every F1 engine must last for all practicing, two qualifying sessions and two races. They are sealed by the FIA and cannot be changed or even opened. Its a real testament to their durability that they should take such abuse over a period of three weeks, all the while revving these little 1.6 litre engines to 19,000 RPM.

I think you may be getting F1 mixed up with NOSCOR which allows engines to be changed/rebuilt with impunity.

Gord Clark
Rockburn, Qué.
Gordon A Clark

A split pin (cotter) should be fitted so that the head fits into the nut slot, this prevents it rotating. The tail cut as it protrudes from the nut and one tail turned up. The short tail prevents the mass from cyclic movements, leaving long tails leaves quite a mass at high engine revs. The cotter is only a safety device and not a retainer. The turn up is only to keep it in place.
I was taught this as a marine engineer, OK marine diesels don't spin at 5/6000 revs, but just imagine the size of pins on a 6" plus diameter bolt.
Ray TF 2884
Ray Lee

If anyone has a set of the Moss/ARP rod bolts, I would be curious to know their exact diameter. Thanks.

Tom
t lange

Hi Ray,

Thanks for reminding everyone of the correct way of fitting cotter pins. Being of 'a certain age' I was also told/learnt to fit the cotters as per your thread.

Cheers,

John
J C Mitchell

I presume "certain age" means that T Types were new when you trained. What the heck happened to the last 60 years?
Ray
Ray Lee

Thanks Gordon - Yes, I am a lot more familiar with NASCAR than I am with F1. My ears prefer the lower pitch but what the F1 guys get out of those small packages is truly amazing. I did not know that they had to run for 2 races and I'm impressed.

Jud
J K Chapin

Fiber locknuts are reused in aircraft quite often. Here's what the FAA has to say on the matter:




Fiber or nylon locknuts are constructed with an unthreaded fiber or nylon locking insert held securely in place. The fiber or nylon insert provides the locking action because it has a smaller diameter than the nut.

Fiber or nylon self-locking nuts are not installed in areas where temperatures exceed 250°F.

After the nut has been tightened, make sure the bolt or stud has at least one thread showing past the nut. DO NOT reuse a fiber or nylon locknut, if the nut cannot meet the minimum prevailing torque values. (See table 7-2)




JE Carroll

Moss bolts are quite good. I fit them in my engine a while back. They fit nicely. If you don't trust the nylok nuts, you can install lock tabs on them as a backup. MGA tabs can be used with minimal modification.
Steve S

Small diameter fiber lock nuts are not included in table 7-2, I was told, because it's difficult to measure the low prevailing torque and they're cheaper to replace than to test and reuse.

I can't of any modern engines that use any locking devices on rod or main bolts, just the proper torque/stretch.
JE Carroll

Steve - I believe Joe is talking about new ARP bolts that Moss is selling now, with (presumably) ARP nuts. No Nyloks, like the older bolts!

Tom Lange
MGT Repair
t lange

Tom, I just bought a set of MOSS ARP bolts and they measure .3135" at the shank(new not torqued yet). An old used TD rod bolt with cotter hole measures .3140" and a new Datsun 12109-B3000 measures .3140". All with digital caliper. What do the bolts you sell measure?
Richard Cameron

All ARP bolts are not alike! There is a considerable difference in size between my bolts and Moss's.

Mine measure .3141" with my very old Etalon shop micrometer, so I guarantee that mine will reliably mic out at .3140. This is intentionally at the high end of the factory spec, since my design and specs were based on MOWOG factory drawings.

I have reliably heard that Moss's dimensions were taken from an old Moss bolt - hence the significant difference in size. Too small and the cap can move on the rod, with potentially disastrous results. If ANY bolts go in finger loose, there is a problem - mine will NOT!

I have been reluctant to bring up this issue because we are competitors - and I sell my bolts for considerably more than Moss (although imitation is the sincerest form of flattery - brass core plugs, ARP rod bolts, superchargers...). I know some of this because in my latest rod bolt order from ARP (EVERY ONE of which I checked with a $20,000 machine), some 50 bolts measured .3135, and I rejected every one of them. When I mentioned this problem to ARP they replaced them with bolts of my diameter, .3140".) Since they exactly duplicate the Moss dimensions, I can only assume they were an over-run from the Moss order, and were sent to me because it was assumed the two products - for the same application - were identical. ARP did NOT supply my proprietary specifications to Moss, so their design is totally their own.

I base my pricing on my cost from ARP, and I assume Moss has greater leverage, and can order larger quantities than I. Moss charges $134.95 plus postage, I charge $230 including postage.

If anyone cares to return their Moss bolts, I will replace them with a set of my bolts at a discounted $200, including Priority shipping.

I'm obviously happy to answer any questions.

Tom Lange
MGT Repair
t lange

I should mention that yesterday I sent out three sets of my ARP rod bolts, to MG racing engine builders. They, and Manley Ford, seem to feel my bolts are better.

Tom Lange
MGT Repair
t lange

I followed the way Steve S. suggestion of fitting MGA lock tabs. See picture.

Willem van der Veer

Thanks to all. I will wire up the main caps. I'm going to go the MGA lock tab route on the big end rod bolts. What type of mods need to be made to the tabs?
Mark Butler

IIRC the 'mods' are just some careful bending to adjust to the XPAG big end profile.
Willem van der Veer

This thread was discussed between 14/05/2014 and 17/05/2014

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