Topic: A Cylinder Rubber Insert Question

[John G]

Number 5 in the picture shows a rubber insert. My cylinder I believe is a 1976 CB750 cylinder. I have it on the engine without the head on and I don't recall putting an insert around where it shows it goes. Is it possible I need to raise the cylinder and stick a rubber insert someplace under there?

[Kevin D]

John, CMSNL has the best parts fiches, many times there are photos of the part, and how many are used.
That part is used 20 times on your CB and it’s a vibration damper tucked in between the fins.


https://www.cmsnl.com/honda-cb750k5-four-1975-usa_model483/rubber-insert_12195300000/

https://www.cmsnl.com/honda-cb750k5-four-1975-usa_model483/rubber-insart_12620286000/

[John G]

Well go figure. I see that now. It appears I need 36 of those to fill all the spots requiring them. Thank you very much. Shows you how observant I am. Hmmmm

[beemerbum]

Why bother? No need for them

[madmtnmotors]

I believe they were used to dampen the "crinkling" sound of the fins after shutdown as the fins cool down. Not required for proper function of the engine.

[PeWe]

I thought they should avoid "fin song" while riding and revving
Not cheap all those plugs.

The fours have resonance just before 5000rpm.
Verified when an exhaust spigot was not really tightened.
I had thoughts about oil orifice was blocked on left side, no oil to cam....
No sound at all at lower rpm made me to think different.

Searched on internet and found resonance talk of typical inline fours on a Kawasaki forum.

[MRieck]

They don't have to go in every hole....every other hole will do it. I have those on hand and can give you a good price on them.

[Don R]

I thought they should avoid "fin song" while riding and revving
Not cheap all those plugs.

The fours have resonance just before 5000rpm.
Verified when an exhaust spigot was not really tightened.
I had thoughts about oil orifice was blocked on left side, no oil to cam....
No sound at all at lower rpm made me to think different.

Searched on internet and found resonance talk of typical inline fours on a Kawasaki forum.

 My blue green 750 K0 has a resonance in the rear fender/ license plate area. I thought it was the exhaust until I got 4-4's and it didn't change.  It has a Cruisin image 836 kit and cam so may be an engine balance issue.

[PeWe]

I thought they should avoid "fin song" while riding and revving
Not cheap all those plugs.

The fours have resonance just before 5000rpm.
Verified when an exhaust spigot was not really tightened.
I had thoughts about oil orifice was blocked on left side, no oil to cam....
No sound at all at lower rpm made me to think different.

Searched on internet and found resonance talk of typical inline fours on a Kawasaki forum.

 My blue green 750 K0 has a resonance in the rear fender/ license plate area. I thought it was the exhaust until I got 4-4's and it didn't change.  It has a Cruisin image 836 kit and cam so may be an engine balance issue.

My engine has balanced crank and it runs well.
This limited rpm area of not felt vibration, but sometimes heard when something is not tightened is the result of the inline 4 design as I wrote.

I remember a biker friend that had a Kawasaki 1000R -83. The passenger footpegs vibrated a lot in around 120/kmh which must be same rpm area.
A CB750 has almost no vibrations at all when compare. Only things not tightened will sing a song

[PeWe]

They don't have to go in every hole....every other hole will do it. I have those on hand and can give you a good price on them.

I thought you must have a good price on them when I got a bunch with the billet block.

I saw the price at CMSNL and they were not cheap.

[John G]

I count 16 places per side where they could go. 17 on the exhaust side with one extra in the center. A total of 33. They are a tight fit. Does anyone have any suggestions on how to install them easily?

[MauiK3]

maybe a good lubricant and a smooth non-metallic v shaped pusher, something like a trim fork for prying on automotive trim
the lubricant could be a water soluble one like Murphy's Oil Soap

[John G]

Thanks MauiK3,
I was thinking the same thing. Now I just have to figure out why the say I need 20 insets and I count 34 suspected places to put them. Hmmmm

[newday777]

Thanks MauiK3,
I was thinking the same thing. Now I just have to figure out why the say I need 20 insets and I count 34 suspected places to put them. Hmmmm

They aren't needed nor came in every hole.
Here are 3 different engines as examples of how they came.

[John G]

Well now that makes sense and why the 20 number comes into play. Excellent. Thanks very much.

[newday777]

Here's a  spare cylinder I have.

[SanDogDewey]

My K2 requires 29 of them for the cylinder and head. I ordered them from CMSNL. I tried to order the light grey ones, but received black ones as suitable subs. I inquired about the grey ones an was told the manufacturer only had a few left. They sent me the grey ones that they had left. CMSNL was great to work with.

[MRieck]

Like I said earlier....I have them in stock and much cheaper than retail.

[SanDogDewey]

Like I said earlier....I have them in stock and much cheaper than retail.

Oops, I missed you earlier comment. Do you have the light grey ones?

[PeWe]

I got light gray type from Mike before.

[Nurse Julie]

A forum member over here in UK manufactures them in grey. We have had many, many sets from him as all the 750/4 engines we restore for customers have a new set fitted. There are 2 types fitted to each engine, one set has a nipple to locate into a hole in the fin, the remainder are without nipples. They reduce fin resonation. Easy to fit, a small dab of grease or silicone spray and push them in place with a 10mm open end spanner.

[PeWe]

"....dab of grease or silicone spray and push them in place with a 10mm open end spanner."

That's how I installed mine in the billet block, really easy. They had small nipples that found the holes when pushing them in