Author Topic: CB750 connecting rods (Read 8710 times)

mrosso · « **on:** December 10, 2007, 03:41:42 PM »

Anyone have suggestions for upgrading '76 CB750 con rods other than the $800+ carrillo pro race stuff?
DOHC CB900?
Forged Aluminum (the ones on ebay)?
Other?

JLeather · « **Reply #1 on:** December 10, 2007, 05:21:41 PM »

Man, I was wondering if anyone ever used those. I see 'em all the time on eBay for under 200 bucks and I always think "Man, I wonder if they're any good". What kinda motors have you used 'em in?

Big Jay · « **Reply #2 on:** December 10, 2007, 09:44:44 PM »

We sold a lot of those back in the day. If I remember correctly, you had to notch the sleever if under 890cc.

Jay

Jerry Rxman Griffin aka MuthaF'er · « **Reply #3 on:** December 10, 2007, 10:51:22 PM »

Daniel,

Can you tell us what the comparative weight of your forged aluminum rods are versus stock rods?

RRRToolSolutions · « **Reply #4 on:** December 11, 2007, 05:26:29 AM »

The stock rods and bolts for my K4 were 355~359 grams. The Carillos were 317 all 4 within .3 grams of each other. By stacking the pins and piston tolerences together you can get them all matched extremely close. Mine came to within .3 for the entire ring/piston/pin/rod assemblies across the 4 holes.

Regards,
Gordon

JLeather · « **Reply #5 on:** December 11, 2007, 05:42:33 AM »

DG,
Were these street motors or mostly race? Anyone got a lot of street miles on these aluminum rods?

Swoop · « **Reply #6 on:** December 11, 2007, 09:42:27 AM »

My 2 cents.
I picked up a motor with an 812 kit in it and those rods, I took it down and couldn't reuse the rods cause the small ends were too badly worn. Don't know the mileage...but I decided not to go with those again.
I am sure there are lots of guys that are waiting for a favorable report....before they take the plunge...I just haven't heard one yet.....other than DG here.

Cyclex' description is not exactly confidence inspiring either....something like ...we don't use them but we know lotsa people that have...or something like that...and they sell them.

Cheers

Steve

754 · « **Reply #7 on:** December 11, 2007, 09:50:35 AM »

Swoop, if you think for sure they are low hrs, might be worth bushing the small end. Depends too what you want to do with the engine and how long you want to run without teardown.

Easy to bore them, and on these if you want to lower deck height a bit it would be easy to do.

mrosso · « **Reply #8 on:** December 11, 2007, 10:33:45 AM »

How about using DOHC rods? Anyone try CB900 rods?

JLeather · « **Reply #9 on:** December 11, 2007, 10:38:01 AM »

I'm sure you've seen Axle's site. It details what needs to be done to run DOHC rods. The DOHC 750 rods are 1.5mm shorter, which significantly drops the CR. The DOHC 900 and 1100 rods work, but as I recall you need to bush them. The wrist-pins on the DOHC 900/1100 are larger than a SOHC750.

cafebob · « **Reply #10 on:** December 11, 2007, 01:06:43 PM »

I just received a set of 750DOHC rods yesterday. Probably will build the motor up Saturday. Ill let you know how it goes.

bob

dusterdude · « **Reply #11 on:** December 11, 2007, 01:16:51 PM »

aluminum rods do stretch,BUT,who`s to say how long it will take and what the stretch tolerance is.

sohc4 · « **Reply #12 on:** December 13, 2007, 06:47:02 AM »

Quote from: JLeather on December 11, 2007, 10:38:01 AM

I'm sure you've seen Axle's site. It details what needs to be done to run DOHC rods. The DOHC 750 rods are 1.5mm shorter, which significantly drops the CR. The DOHC 900 and 1100 rods work, but as I recall you need to bush them. The wrist-pins on the DOHC 900/1100 are larger than a SOHC750.

The 900 DOHC rods are 1.5mm longer than stock, like the 1100 rods. The 1100 have a 17mm small end (15mm is stock).

Geeto67 · « **Reply #13 on:** December 13, 2007, 07:57:52 AM »

does anyone know for certain that the 900 rods are actually stronger than a stock SOHC rod? The DOHC motors were more fragile than the SOHC counterparts, I don't remember them having any rod problems but there were all sorts of other mechanical issues with those motors.

mrosso · « **Reply #14 on:** December 13, 2007, 12:28:34 PM »

JLeather said there might be a way to put bushings into the CB900 rods to accomodate CB750 pistons. I have a Wiseco 836cc kit I want to put into my '76 motor. Would putting bushings in the rods work for these pistons? What kind of bushing materials? Tolerances?

754 · « **Reply #15 on:** December 13, 2007, 05:36:15 PM »

If the small ends are bigger just use bushings. Make them out of 660 bronze or similar. Make them pin size or a .001 under and give the OD abour .001 -.0015 press fit. then either very carefully ream (if you are good at it) or get an engine shop to pinhone them.

sohc4 · « **Reply #16 on:** December 14, 2007, 04:55:12 AM »

The 900DOHC rods have a 15mm small end which will fit the stock wrist pins. No need for bushings. Only the 1100DOHC has the 17mm ends, both the 750DOHC and the 900DOHC have 15mm, just like the 750SOHC.

Geeto67 · « **Reply #17 on:** December 14, 2007, 01:15:33 PM »

I mentioned this post this on the DOHC forum and the opinion so far is the DOHC 750 and 900 rods are still considered fairly weak if not as weak as SOHC 750 rods. So I don't really see the advantage in DOHC 750 or 900 rods.

It was also mentioned that the 1100f rods might be stronger, because of having to accomidate the 17mm wristpin, but there is still the issue of bushing them.

cafebob · « **Reply #18 on:** December 14, 2007, 01:43:40 PM »

still a way (probably not the best $:-\$ )to drop your compression. I will post pictures of the 2 side by side tonight or tomorrow.

bob

mrosso · « **Reply #19 on:** December 14, 2007, 02:24:37 PM »

Hey! Just popped onto Cycle eXchange's website. Ken is announcing a new set of con rods to be available in the spring for about $525. Anyone know anything about this? Just may be the happy median between $1000 racing rods and stock CB750 sohc rods.

Big Jay · « **Reply #20 on:** December 16, 2007, 02:44:19 PM »

Quote from: mrosso on December 14, 2007, 02:24:37 PM

Hey! Just popped onto Cycle eXchange's website. Ken is announcing a new set of con rods to be available in the spring for about $525. Anyone know anything about this? Just may be the happy median between $1000 racing rods and stock CB750 sohc rods.

China? Lot of that coming into the country now and marketed under very American sounding names.

Jay

sohc4 · « **Reply #21 on:** December 17, 2007, 05:07:14 AM »

For pictures of the various DOHC rods vs stock SOHC look here:

http://www.satanicmechanic.org/conrods.shtml

Cheers,
Axl

Big Jay · « **Reply #22 on:** December 17, 2007, 09:36:33 AM »

Quote from: dgfischer on December 16, 2007, 03:57:23 PM

Hey, Jay
What was your experiences with the rods that started this thread ?
You probably sold more of them than anyone.
DG

See post 4

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Author Topic: CB750 connecting rods (Read 8710 times)

Swoop

sohc4

sohc4

sohc4