Topic: R.C engineering parts question

[caferacer77]

Hey guys,
I am rebuilding my cb750 motor and I am finally going to try to see if I can use some of the parts I have had forgotten in a box. Can anyone confirm that these are R.C. Engineering, con rods? I am assuming that since they say R.C. stamped on them they should be. The problem is that two out of the four have been machined down slightly. Are these still usable if all four con rods are machined down the same and put on a scale to make sure they are exactly the same weight? Also they have some kind of a numbering system stamped on them but they don't match. Two of the con rods have S6B, one has S5O, and the other S4A. Anyone know if that means they are not matching even though they look exactly the same?
Second question, I was given as set of the retainers shown in the pics, are these R.C. Engineering titanium retainers, that’s what I have been told, but I have no way of confirming.
Thanks
fabrizio


 

[mkramer1121]

i think red is aluminum, at least that is what i have seen.  titanium would be silver.  also, rc used stock rods and shot peened them and used stronger bolts, so yes, those look like rc rods, however i would have them balanced at the least prior to using them.

[754]

You have,
Super Hi-Perf Rods Same a #HPR but fitted with special heavy-duty rod bolts 11/32 INCH. High tensile automotive bolts are used.These bolts are approximately four times stronger than standard units. Recommended in any motor that is used in serious racing.

They had 2 types reworked rods, those are the stronger ones.

Your springs look like they have aluminum collars. You may be able to tell by weight.

[JLeather]

If you're just building a mild motor and don't really need those RC rods I could definitely use 'em for my turbo build up.  Lemme know.

[caferacer77]

thanks for the replyes guys. I really appreciate the info. I think I will try and use them, I am still a little concerned about how they are machined because the top of the connecting bolts are machined down a bit on two of those rods, and I am relaly concerned that their integrity has been compromised. Is there a way to replace the bolts that have been machined down or even anyone that will do it? I'll definately send them to a good machine shop and make sure they are balanced and weigh the same.
f.

[City Boy]

I can confirm that the retainers are alum. I have them installed in my unit.  Rock On

[Terry in Australia]

I've got RC modified rods in my 836cc engine, and they seem to be holding up well, after several 11000+ RPM thrashings.

I can't comment on how strong yours are after that "machining" that you mention, but as long as it was done by RC and not by some Wally with an angle grinder, they should be fine. Cheers, Terry.

[754]

Geez Terry, my stock rods did that in my 836 for a few decades, but I wouldnt recommend using them..

[Terry in Australia]

Yeah, I think stock rods in a mild engine are pretty good too Frank, my K2 engine has seen plenty of 10,000+ RPM action (especially with the F2 carbs) with no ill effects, but that engine is a freshly rebuilt stocker. Cheers, Terry.

[caferacer77]

for now i will only install an 836 kit, but i want to do extensive work to the bottom end...lightening and balancing crank, undercut transmission, new primary chain, etc. i am also considering a CB750A crankshaft. i really want to make sure I put together a good bottom end. i am hoping to get good HP out of this engine. If I can still use these rods I'll feel a lot more secure when redlining this it. I called APE they said they will inspect them for me and give some recommendations. Anyone can recommend another qualified machine shop that would know about these RC parts?
thanks
fabrizio

[Terry in Australia]

Send 'em to Big Jay at APE mate, he's a member here, and probably knows more about hot-rodding our bikes than anyone else in the free world. Cheers, Terry.

[MCRider]

thanks for the replyes guys. I really appreciate the info. I think I will try and use them, I am still a little concerned about how they are machined because the top of the connecting bolts are machined down a bit on two of those rods, and I am relaly concerned that their integrity has been compromised. Is there a way to replace the bolts that have been machined down or even anyone that will do it? I'll definately send them to a good machine shop and make sure they are balanced and weigh the same.
f.

Usually, often, the machining on the top of the rod IS the balancing. Prior owner or manufacturer balanced them most likely, esp since its only on 2 of them. The top part of the small end of the rod is the place of least stress, so that's where the maching is done to balance them. Still you should get them balanced before use to eliminate any variable with age.

Also, grinding on the bolt is the second choice for the balancing act. Any good speed shop has bolts and no you should not use used bolts ever. Once they've been torqued, they are done.

The RC HP rods were forged steel with the same cross section as stock, except that the small end is visibly beefier than stock, and the boss the pin goes through is beefier as well. The big end was not much different visibly except for the larger bolts. If you haven't seen a stock rod, it would be hard to know the difference.

[Beemer]

Personally I'd use these rods as is, but have the balance checked.  The grind marks MIGHT be for clearance in an 1170 stroker motor. I had RC's GOLDEN rods and those had to be ground a LOT to clear the crank and the cases.  They did wind up grinding the tops of the rod bolts on two of them, IIRC. 

Grinding on the top of the rod bolt won't hurt it within reason.  I've been racing for 36 years now, and I have YET to see a rod bolt fail because the head snapped off or the bolt pulled thru the rod.  they snap in the middle or on the ends most of the time due to bolt stretch.

It could be that your rods were used in a stroker motor at one time.  There were several varieties depending on what class you were racing and the displacement limit for the class, and whether you were road racing or drag racing.

For instance, you might want a longer stroke, higher torque motor for a tight course where all you get is a fast grunt from corner to corner.  However, if you had a lot of wide open straightaways or were drag racing, you'd want short stroke and BIG bore. 

My 1170 was set up for road racing, but did equally well drag racing simply because of its size and weight versus the 1100cc competition, which usually weighed in at my bike's weight with ME on it..  You'd be suprised what you can get these bikes down to weight wise if you dump all the extra stuff you don't need on the track.  A buddy was to the point he was shaving the cases and using aluminum tubing for the seat and fender supports (bolted to the steel frame with a tab) and he even made an aluminum seat pan, aluminum footpegs, and he even ground the carb bodies down to pare weight.  I think his bike got down to around 425 pounds when it was all said and done, but he was using titanium (unobtainium for me) bolts as well..and those were HOLLOW.  Hollow axles, hollow camshafts, crank had hollow journals and god knows what else he used.  If we'd have had carbon fiber back then, he'd have had his fuel tank and body work made out of it, along with his brake rotors.  (he even ground the brake calipers down, swiss cheesed them, and he found the lowest friction axle bearings made as well.  His fairing, WITH stays, was under a pound and a half for a full race fairing.

I know, a bit off topic. 

I just bought two sets of forged aluminum rods off ebay for under 200 bucks a set..made in japan, not china. 

As for the RC rods, run them..they're about as bullet proof as you'll find!

Dave

[Ricky_Racer]

Hi Dave!  I've got a set of fresh RC Golden Rods that I've been thinking of running on a blower or turbo motor, but all the hoopla surrounding the stretching of aluminum rods has me a little leery. What is your experience with the Golden Rods? And when you mentioned grinding for clearance, did that strictly apply to the stroker crank or would the Golden Rods require clearancing with a standard crank?  Thanks!  RR

[754]

Goldenrods are milled from billet and have a longer lifespan than forged aluminum rods.. should be good still.

[Ricky_Racer]

Thanks, 754! That makes perfect sense, and these rods look virtually unused so I guess they're gonna get run after all. They're so pretty that I hated to not use them! LOL.

Thanks again for the quick response!  RR

[754]

Try to get a weight on them..

Check length as they came in 2 lengths..1/4 in difference

If you do decide to sell them, let me know..

[Ricky_Racer]

Thanks! I'll have the length and weight checked and get back with you. RR