Author Topic: 750 connecting rod orientation  (Read 291 times)

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Offline sammon287

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750 connecting rod orientation
« on: September 18, 2019, 02:59:00 pm »
Letter marking on big end facing forward and numbers back? I seem to remember that, but I took it apart a long time ago and couldn't find it in a search. Does it matter? They seem pretty symmetrical. New bearings and bolts/nuts for what it's worth.
1976 CB750A

Offline sammon287

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Re: 750 connecting rod orientation
« Reply #1 on: September 20, 2019, 10:30:44 am »
No replies, so I put them all in with the letters facing forward. About to seal it all up. No going back now.
1976 CB750A

Offline ttr400

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Re: 750 connecting rod orientation
« Reply #2 on: September 20, 2019, 10:21:34 pm »
Bearing tangs facing towards the exhaust side.

Kevin
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Offline PeWe

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Re: 750 connecting rod orientation
« Reply #3 on: September 21, 2019, 01:34:41 am »
I should look for cranks with rods for sale on eBay and see how they look like. If 3 different cranks + rods look the same, that's it.
CB750 K6-76 1005cc JMR Billet block.
CB750 K2-75 Parts assembled to stock K2

Offline sammon287

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Re: 750 connecting rod orientation
« Reply #4 on: September 21, 2019, 04:18:12 am »
Bearing tangs facing towards the exhaust side.

Kevin

Not sure what you mean by bearing tangs. I thought bearing tangs were the little tabs that laterally locate each bearing shell, so there is one on the rod and one on the rod cap. Either way, I sealed it all up with Honda bond yesterday with letter side facing forward/exhaust.
1976 CB750A

Online Bodi

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Re: 750 connecting rod orientation
« Reply #5 on: September 21, 2019, 11:09:20 am »
Yes those tabs are the tangs, to keep the shells from rotating in the rod. There's tapered cutouts in the rod and cap for them. It's best to have the rods so the tangs are oriented to butt against the opposite part against the rotation of the crank, the tapered cutouts can flatten the tangs out and let the shells spin if the rods are the other way around.
Main bearings... you can't change the cases around, just put the shells in the right way.
I don't know if this is absolutely necessary or just a good practice.

Offline sammon287

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Re: 750 connecting rod orientation
« Reply #6 on: September 21, 2019, 05:49:45 pm »
I get what you are saying now. Without splitting the cases and pulling at least one rod cap, I can't look to see if the tabs are braced against the crank rotation. I assume the weight markings and bearing size markings are always on the same respective sides, so I hope weight letters facing forward is correct.   
1976 CB750A

Offline RAF122S

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Re: 750 connecting rod orientation
« Reply #7 on: September 22, 2019, 12:58:21 am »
Better to go through the trouble of pulling the bottom case off and check now than to discover it was backwards if it rises its head to bite you in the butt sometime later. But I am cautious.
David stuck in the curvy back roads of "Upper East" TN

Offline bryanj

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Re: 750 connecting rod orientation
« Reply #8 on: September 22, 2019, 11:40:12 am »
If it was critical Honda would say so in the blue book manual----NOT HAYNES, CLYMER OR ANY OTHER SPURIOUS PRINTING
Semi Geriatric ex-Honda mechanic and MOT tester (UK version of annual inspection). Garage full of "projects" mostly 500/4 from pre 73 (no road tax in UK).

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Offline kmb69

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Re: 750 connecting rod orientation
« Reply #9 on: September 22, 2019, 01:40:26 pm »
Bearing tangs facing towards the exhaust side.

Kevin

Kevin is correct.

If it was critical Honda would say so in the blue book manual----NOT HAYNES, CLYMER OR ANY OTHER SPURIOUS PRINTING

Honda does say via the oiler hole orientation in the DOHC manuals.
« Last Edit: September 22, 2019, 06:01:39 pm by kmb69 »

Offline sammon287

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Re: 750 connecting rod orientation
« Reply #10 on: September 22, 2019, 05:49:08 pm »
  I looked at four or five crankshafts for sale on Ebay with con rods still attached. All of the con rods are oriented with the letter stamps forward (exhaust) and the number stamps back. Looks like I will be OK without re-splitting the cases and pulling a rod cap.
1976 CB750A

Offline sammon287

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Re: 750 connecting rod orientation
« Reply #11 on: September 22, 2019, 05:51:54 pm »
I should look for cranks with rods for sale on eBay and see how they look like. If 3 different cranks + rods look the same, that's it.

Thanks for the idea.
1976 CB750A

Offline disco

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Re: 750 connecting rod orientation
« Reply #12 on: September 22, 2019, 07:45:16 pm »
I just took some pics of a spare CB750 rod I had lying around. It’s from a ‘76 model I believe. As you can see if you align the cap so that both halves of the stamped letter matches up, then you end up with both tangs on one side. One tang faces up & the other down. So only one tang can ever oppose the crank rotation.

So, I don’t think the tang argument is valid.
« Last Edit: September 22, 2019, 09:14:34 pm by disco »
1976 CB750 K6 Sapphire Blue
1972 CB750 K2 836 Orange Sunrise
1972 CB750 K2 Candy Red
1972 CB750 K2 Candy Gold'

Offline PeWe

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Re: 750 connecting rod orientation
« Reply #13 on: September 22, 2019, 09:41:52 pm »
I should look for cranks with rods for sale on eBay and see how they look like. If 3 different cranks + rods look the same, that's it.

Thanks for the idea.
Photos have helped me many times. I've found photos on this forum about how things look like when they look strange.
CB750 K6-76 1005cc JMR Billet block.
CB750 K2-75 Parts assembled to stock K2

Offline scottly

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Re: 750 connecting rod orientation
« Reply #14 on: September 22, 2019, 10:48:27 pm »
I just took some pics of a spare CB750 rod I had lying around. It’s from a ‘76 model I believe. As you can see if you align the cap so that both halves of the stamped letter matches up, then you end up with both tangs on one side. One tang faces up & the other down. So only one tang can ever oppose the crank rotation.

So, I don’t think the tang argument is valid.
The tang would help with the shell in the rod end, which takes the greatest load, but the main thing that "locks" the bearing shells in the rod end is called "crush". The ends of the shells protrude slightly from the mating surfaces of the cap and rod, and tightening the rod bolts compresses the shells firmly against the rod bore. This is one reason not to re-use bearing shells once they have been assembled, as they may have lost some of the crush.
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