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Author Topic: CB750K7 rebuild, bad sound from engine  (Read 4454 times)

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Offline stou

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Re: CB750K7 rebuild, bad sound from engine
« Reply #25 on: October 10, 2018, 11:18:28 am »
754, the cam chain is new. But the primary chain has not been changed. I agree with you, if there's some friction, I must see some scuffed area. I will remove everything in the crankcase and look carefully everywhere.

enwri, there's no float on the crankshaft in the old engine, 0mm.

When we listen to that noise, it is really look like a chain noise. So I'm pretty sure if I replace the starting gear seal to eliminate the free play in the crankshaft and put new primary chain, this must eliminate the noise.

But I'll do a more detailled examination after removing every parts from the crankcase to se if I can see a scuffed area.

Thanks for your comments!
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Honda CB750K7 1977
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Offline MauiK3

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Re: CB750K7 rebuild, bad sound from engine
« Reply #26 on: October 10, 2018, 03:18:53 pm »
Do the primary tensioner too.
Just to be sure.
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Offline stou

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Re: CB750K7 rebuild, bad sound from engine
« Reply #27 on: October 10, 2018, 03:28:34 pm »
Yes the CMSNL kit is the 2 chains and the tensioner.
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Offline Tracksnblades1

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Re: CB750K7 rebuild, bad sound from engine
« Reply #28 on: October 10, 2018, 05:46:47 pm »
Did you replace them rubber cushions ...?
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Offline enwri

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Re: CB750K7 rebuild, bad sound from engine
« Reply #29 on: October 10, 2018, 06:12:39 pm »
I could not find a measurement for the end float clearance, surely there is one somewhere. 4mm has to be too much but if there is not enough, it will quickly make its own, destructively. (This is obvious, just covering my arse.) ;)
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Offline stou

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Re: CB750K7 rebuild, bad sound from engine
« Reply #30 on: October 10, 2018, 07:27:59 pm »
Quote from: Tracksnblades1 on October 10, 2018, 05:46:47 pm
Did you replace them rubber cushions ...?


...You do have a thrust bearing...?

Which rubber cushions?

The thrust bearing on the primary gear?

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Honda CR125M1 1974
Honda CB750K7 1977
Honda TLR200 1986
OSSA TR280i Trial
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My CB750 build: http://forums.sohc4.net/index.php/topic,174710.0.html

Offline scottly

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Re: CB750K7 rebuild, bad sound from engine
« Reply #31 on: October 10, 2018, 07:37:50 pm »
The end-play on the crankshaft is controlled by machined surfaces on the sides of the main bearing journals in the crankcase, and the seal on the starter gear has nothing to do with it.
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Offline Tracksnblades1

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Re: CB750K7 rebuild, bad sound from engine
« Reply #32 on: October 10, 2018, 08:46:26 pm »
From a later k.
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Offline Tracksnblades1

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Re: CB750K7 rebuild, bad sound from engine
« Reply #33 on: October 10, 2018, 09:10:46 pm »
I borrowed this from another post. The rubber cushions are disintegrated in the primary drive hub in the photo, but it could be a source of noise also.
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Offline Tracksnblades1

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Re: CB750K7 rebuild, bad sound from engine
« Reply #34 on: October 10, 2018, 09:32:36 pm »
MessierMoto, i.e. Mirko has provided this link for HD primary Chains. You may read, most forum members agree the HD variants are desirable in the big bore engines.

https://www.ebay.com/itm/Steuerkette-SWAG-30-93-9962-/161555573484?rmvSB=true

I purchased much pricier ones that Mirko indicated were the same as this link, but I don't read German.

Good luck chasing them gremlins out.
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Offline enwri

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Re: CB750K7 rebuild, bad sound from engine
« Reply #35 on: October 10, 2018, 11:39:45 pm »
Quote from: scottly on October 10, 2018, 07:37:50 pm
The end-play on the crankshaft is controlled by machined surfaces on the sides of the main bearing journals in the crankcase, and the seal on the starter gear has nothing to do with it.

Ooh, that's bad news.  :(

Unless those surfaces are in the top case, then maybe not.
« Last Edit: October 10, 2018, 11:45:03 pm by enwri »
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Offline gp_st3

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Re: CB750K7 rebuild, bad sound from engine
« Reply #36 on: October 11, 2018, 03:20:58 am »
They are indeed in the top case and only the journal between cylinder #1 & #2 (on my K4 at least)
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Offline stou

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Re: CB750K7 rebuild, bad sound from engine
« Reply #37 on: October 11, 2018, 03:32:52 am »
Quote from: scottly on October 10, 2018, 07:37:50 pm
The end-play on the crankshaft is controlled by machined surfaces on the sides of the main bearing journals in the crankcase, and the seal on the starter gear has nothing to do with it.

Good info! I just check the width and I have 22.83mm. According to the picture Tracksnblades1 posted, the limit is 22.75. So that's fine.

Tracksnblades1, where did you find that info, I can't see it in my shop manual?
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Honda CR125M1 1974
Honda CB750K7 1977
Honda TLR200 1986
OSSA TR280i Trial
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My CB750 build: http://forums.sohc4.net/index.php/topic,174710.0.html

Offline stou

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Re: CB750K7 rebuild, bad sound from engine
« Reply #38 on: October 11, 2018, 03:37:47 am »
Quote from: Tracksnblades1 on October 10, 2018, 09:10:46 pm
I borrowed this from another post. The rubber cushions are disintegrated in the primary drive hub in the photo, but it could be a source of noise also.

I'll check if there is any free play in this primary gear, thanks!
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Honda CR125M1 1974
Honda CB750K7 1977
Honda TLR200 1986
OSSA TR280i Trial
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My CB750 build: http://forums.sohc4.net/index.php/topic,174710.0.html

Offline Tracksnblades1

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Re: CB750K7 rebuild, bad sound from engine
« Reply #39 on: October 11, 2018, 05:20:57 am »
In the shop manual indeed..The F2/K7 supplement, the photo I copy/pasted from the same on any flip online.The rubber cushions are 41 years old and you have an 836 kit. Cyclex , APE and others stock them and provide replacement services if you decide you don't want to.  cyclex advertises to balance that assembly also.

Have you  definitely found the source of the noise?

Don't forget those new chains? My came from Germany in 10-12 day without checking the tracking number.
« Last Edit: October 11, 2018, 05:34:02 am by Tracksnblades1 »
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Offline enwri

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Re: CB750K7 rebuild, bad sound from engine
« Reply #40 on: October 11, 2018, 06:24:37 am »
Quote from: enwri on October 10, 2018, 11:39:45 pm
Quote from: scottly on October 10, 2018, 07:37:50 pm
The end-play on the crankshaft is controlled by machined surfaces on the sides of the main bearing journals in the crankcase, and the seal on the starter gear has nothing to do with it.

Ooh, that's bad news.  :(

Unless those surfaces are in the top case, then maybe not.
Quote from: gp_st3 on October 11, 2018, 03:20:58 am
They are indeed in the top case and only the journal between cylinder #1 & #2 (on my K4 at least)


At least I kept you bumped to the top of the page, I'll just sit over here and watch, :)

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77 CB 750 k.. 29 years and counting.
91 TDM 850 (No.34) so comfy and soft
8? XJ 550 meh...
76 XL 350 Super Sport stump puller..
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Offline stou

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Re: CB750K7 rebuild, bad sound from engine
« Reply #41 on: October 11, 2018, 07:51:33 am »
Quote from: Tracksnblades1 on October 11, 2018, 05:20:57 am
In the shop manual indeed..The F2/K7 supplement, the photo I copy/pasted from the same on any flip online.The rubber cushions are 41 years old and you have an 836 kit. Cyclex , APE and others stock them and provide replacement services if you decide you don't want to.  cyclex advertises to balance that assembly also.

Have you  definitely found the source of the noise?

Don't forget those new chains? My came from Germany in 10-12 day without checking the tracking number.

I have the K1-K8 supplement and I don't see anything about that. But anyway from the specs on the picutre you posted, it is ok.

I have checked the primary gear. I have a bad and a good news. The bad news is the there is a free play between the 2 primary gears. Not a lot but some. The good news is the one on the other engine I have, look fine, no free play.

So I will swap the gear. For now I puted enough money on that bike and if it work fine with this other gear, it will do the job for now.

About the primary chain, the CMSNL kit is already on his way.
https://www.cmsnl.com/honda-cb750k7-four-canada_model14396/chain-kit_00000kit0017/#.W79iQMtPHyQ

I think with the seal replacement, new primary chain and tender, and primary gear swap, it will be good. We will see in a week or so, when I'll receive everything and reassemble the engine.
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Honda CR125M1 1974
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Offline Tracksnblades1

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Re: CB750K7 rebuild, bad sound from engine
« Reply #42 on: October 11, 2018, 05:40:43 pm »
Ok, 👍,
Have you found the source of the noise..?
Addressed the loose starter gear...?
Addressed the excessive play in kick starter..?
Verified clutch and Trans parts are good...?
Was this bike running before you rebuilt it...?
Was the noise in it before you rebuilt it...?
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Offline Tracksnblades1

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Re: CB750K7 rebuild, bad sound from engine
« Reply #43 on: October 11, 2018, 06:16:13 pm »
Stou,

Listen to the linked YouTube video "Honda cb750 loose kickstart gear".
Sounds like your noise...?


Find the source of your play.
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Offline Tracksnblades1

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Re: CB750K7 rebuild, bad sound from engine
« Reply #44 on: October 11, 2018, 06:33:38 pm »
See if your assembly has all these goodies...

« Last Edit: October 11, 2018, 06:38:02 pm by Tracksnblades1 »
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Offline stou

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Re: CB750K7 rebuild, bad sound from engine
« Reply #45 on: October 11, 2018, 07:49:31 pm »
Here's some anwers to your questions Tracksnblades1:

Have you found the source of the noise..?
      I'll really see if it's ok when I'll start the bike next week once rebuild

Addressed the loose starter gear...?
      I removed the stator and replaced the seal. This make no real differences. Not even 1mm difference. I think once the pistons are in the cylinder, it can't really move sideway.

Addressed the excessive play in kick starter..?
      I did some test while the base casing are open. If I screw the clutch cover, it push on the shaft and there's no rubbing anywhere. Also, there's no scuffed area. So I don't think this is a problem.

Verified clutch and Trans parts are good...?
      I checked everything in the trans, and it's all good. No abnormal wear or scuffes.

Was this bike running before you rebuilt it...?
      No. I did start it after some repair but it does not runed correctly.

Was the noise in it before you rebuilt it...?
      Since it wasn't running correctly, there was many noise. The cam chain was really worn out and piston and ring was really out limit. Compression was very low. So I can't tell.


With the replacement of the primary gear, which has some free play, and new primary chains and the tensioner, I'm confident that this is the cause of the noise. I was really surprise to know that there's some rubber cushion between the two primary gears. I was able to move a little bit the two gears independently from front to back. The other one used to replace the one in the engine didn't have any play. I really hope this will correct the problem. But there's no way to be sure before hearing it running!


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Honda CR125M1 1974
Honda CB750K7 1977
Honda TLR200 1986
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My CB750 build: http://forums.sohc4.net/index.php/topic,174710.0.html

Offline Tracksnblades1

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Re: CB750K7 rebuild, bad sound from engine
« Reply #46 on: October 11, 2018, 08:53:23 pm »
One more, check that oil pump. See if it's responsible for wearing out the kickstart gear assembly.

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Offline stou

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Re: CB750K7 rebuild, bad sound from engine
« Reply #47 on: October 13, 2018, 04:58:55 pm »
I checked the gear and the shaft of the kickstart. The gear is ok anf the shaft is near the limit. But it is not worn enough to make noise.

But thanks anyway for the info!
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Honda CR125M1 1974
Honda CB750K7 1977
Honda TLR200 1986
OSSA TR280i Trial
KTM 890 Adventure R 2021
My CB750 build: http://forums.sohc4.net/index.php/topic,174710.0.html

Offline stou

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Re: CB750K7 rebuild, bad sound from engine
« Reply #48 on: October 15, 2018, 09:22:30 am »
I received the parts this morning. They are Honda parts. I installed it in the cranckcase and the difference is really big. Watch the video with the old chain and the one with the new chain. Even if according to the shop manual it is under the specs <70mm, there's to much wear.

New chain: Not a valid vimeo URL
Old chain: Not a valid vimeo URL
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Honda CR125M1 1974
Honda CB750K7 1977
Honda TLR200 1986
OSSA TR280i Trial
KTM 890 Adventure R 2021
My CB750 build: http://forums.sohc4.net/index.php/topic,174710.0.html

Offline bear

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Re: CB750K7 rebuild, bad sound from engine
« Reply #49 on: October 15, 2018, 09:01:46 pm »
I would suggest you have one of your used cush drive's refubished.
Replacing your primary chains without replacing the cush drive rubbers will only result in premature wear to your chains and you will be back to square one.

Cheers,
Brian
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