Topic: primary chain preventive maintenance

[sammon287]

  I understand the 750A primary chain is pretty strong and reliable. Mine looks fine with 18k miles.  The fixed guides on the top and bottom case also look OK, with no significant wear or gouges. Aside from various oil leaks, the reason I completely stripped the engine was to look for mechanical causes for the loud clacking noise on cold start and low idle. I always thought it was from the primary chain, and since everything else looks perfect, I still do. I wonder if the hardness of the old guides makes the noise worse. Only one of the two guides is available from CMSL and it's expensive. Are they normally pretty hard, or should the guide be more flexible? Should I bother replacing the expensive chain with only 18k miles? Should I just expect to still have that awful noise after a full engine rebuild? (It's not together yet)

[kmb69]

  I understand the 750A primary chain is pretty strong and reliable. Mine looks fine with 18k miles.  The fixed guides on the top and bottom case also look OK, with no significant wear or gouges. Aside from various oil leaks, the reason I completely stripped the engine was to look for mechanical causes for the loud clacking noise on cold start and low idle. I always thought it was from the primary chain, and since everything else looks perfect, I still do. I wonder if the hardness of the old guides makes the noise worse. Only one of the two guides is available from CMSL and it's expensive. Are they normally pretty hard, or should the guide be more flexible? Should I bother replacing the expensive chain with only 18k miles? Should I just expect to still have that awful noise after a full engine rebuild? (It's not together yet)

Check the springs in the primary damper. I have yet to tear an automatic down that did not have primary damper springs busted up in multiple pieces.

[RAFster122s]

Check piston skirts for signs of wear and skuffing. Piston slap makes an awful racket until warmed up.

[Medyo Bastos]

Sync carbs


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[sammon287]

  I understand the 750A primary chain is pretty strong and reliable. Mine looks fine with 18k miles.  The fixed guides on the top and bottom case also look OK, with no significant wear or gouges. Aside from various oil leaks, the reason I completely stripped the engine was to look for mechanical causes for the loud clacking noise on cold start and low idle. I always thought it was from the primary chain, and since everything else looks perfect, I still do. I wonder if the hardness of the old guides makes the noise worse. Only one of the two guides is available from CMSL and it's expensive. Are they normally pretty hard, or should the guide be more flexible? Should I bother replacing the expensive chain with only 18k miles? Should I just expect to still have that awful noise after a full engine rebuild? (It's not together yet)

Check the springs in the primary damper. I have yet to tear an automatic down that did not have primary damper springs busted up in multiple pieces.

  I can only find reference to primary damper springs in the 400A. Is this a thing on 750A's also?

[kmb69]

.....
  I can only find reference to primary damper springs in the 400A. Is this a thing on 750A's also?

Yes. They are in the primary gear driving the torque converter outer/pump.
This is the biggest design flaw in the Automatics in my opinion.
Honda had room to put a nice damper system in the HyVo primary gear/sprocket.

JTMarks77 sells replacements on eBay:
https://www.ebay.com/itm/Honda-750-Input-Shaft-23110-393-010-23110-393-020-23110-393-030-Springs-CB750A/331671472951?hash=item4d39290b37:g:LbIAAOSwLF1X48mQ

[sammon287]

Great info. Thanks. Should I replace the springs even if mine aren't broken? I was considering not doing any further disassembly, but now I'll take that sub-assembly apart. I think I have some gaskets for it.

[kmb69]

Great info. Thanks. Should I replace the springs even if mine aren't broken? I was considering not doing any further disassembly, but now I'll take that sub-assembly apart. I think I have some gaskets for it.

I would say at 18k miles, yes. Be surprised if none are broken. If you already have the cases split to address the primary, it's the perfect time. No additional gaskets needed if the cases are open.

[sammon287]

  I'll definitely replace them. Thanks for the tip. I still have to order rings, bearings, and a few other things anyway.

[sammon287]

I just looked and my springs are broken. I have never been happy to find broken parts before. Maybe their replacement will help with the noise I was hearing.

[jukku]

Pics of ok and broken spring.

[underdog]

    Are the replacement springs any better? Replacing bad product with the same doesn't really make sense. My thought is that since its an auto, perhaps simply making it solid might be more sensible. Has anyone tried this? A few of mine were broken also, and I was advised to just put it back together that way because they'll break shortly anyway, particularly with a higher HP engine. I'm just pondering the problem and considering ideas. 

[kmb69]

    Are the replacement springs any better? Replacing bad product with the same doesn't really make sense. My thought is that since its an auto, perhaps simply making it solid might be more sensible. Has anyone tried this? A few of mine were broken also, and I was advised to just put it back together that way because they'll break shortly anyway, particularly with a higher HP engine. I'm just pondering the problem and considering ideas. 

Damn good question that I can't answer. I bought some of JT's springs and they appear to be aftermarket. Rebuilt one of my dampers with them but I have not run it yet. They look better to me than the originals but maybe that's wishful thinking. Maybe somebody on the forum can provide some feedback since JT has sold a bunch of those replacement sets.

Not sure about running the primary solid even though we have a torque converter. Honda must have believed they needed a damper system to make them to come up with the clusterf#$k they came up with.

I am building an automatic based dragbike right now and am running that gear solid but have designed a damper for the primary shaft cause I just don't know.

[underdog]

 I'm just finishing up my auto dragbike as well and I'm second guessing myself for putting it back together that way. As it relates the this thread, I cant imagine all that slack  is very healthy for the primary chain either. Probably less for us because we likely have the springs compressed at the staring line, but every motion from throttle open to closed must have some sort of hit to it.

[sammon287]

I have the input shaft/damper disassembled and noticed there are punch marks on the inside of the damper side plates (one on each) that press onto the shaft. If the dots are aligned with each other for reassembly, the ports for the springs and pins don't line up. Is there anything to consider when pressing the splined parts back on the input shaft? I oriented one of the four small notches inside the first plate with the oil feed hole on the splined part of the shaft. That makes more of the oil hole clear before the other parts are pressed on.