Engine sound after installing upgraded horseshoe (tensioner)

[Erwin83]

Hi everyone
Last year I finally bit the bullet and opened my 400/4 cases as I had the dreaded hairline crack in the bottom half. Got that welded.
As a “while I am there”, I also changed out the cam chain tensioner for the CNC version with bearing.
So now, starting to ride my CB again this spring, in the first time in 18 years of ownership, I have no more oil leaks and a properly tensioned Cam chain!

So much so, that I have to get used to the engine noise all over again. And I hate mechanical noises I cannot exactly identify...
I have a slight humming/whining noise that I think is the chain going over de guides. Do you recognise this change in sound after installing the upgraded tensioner? Bike runs good across the complete rev range.

[McCabe-Thiele (Ted)]

Have you checked the cam chain adjustment again to be sure its not too tight?

[Erwin83]

Can it be too tight? It’s purely spring loaded right? I have not pushed on the rod or anything, just release the clamping bolt and tighten again.

[McCabe-Thiele (Ted)]

Can it be too tight? It’s purely spring loaded right? I have not pushed on the rod or anything, just release the clamping bolt and tighten again.

Thinking about it probably not but, when I adjusted mine after the rebuild I did not adjust it as per the manual with the engine running. I did it the static way by releasing the pinch bolt pushing down on the kick start then with the chain tensioned tightened the bolt.

Just a though my top cap cover that sits above the actuation  rod was I thought  touching the plunger rod when I first  nipped it down by hand. I put a copper washer between the cap and the block to give it some clearance as I felt it was pushing the rod down. I had fitted new chain & guides but it was the original horseshoe.

[Erwin83]

Come to think of it, I did actually tighten the chain static, with an eye on the chain, rotating the engine to bring the chain in a position where all slack was on the tensioner side. And I could actually see it spring to tension when releasing the rod.
Maybe I should redo the procedure according to the manual, with engine running...

I'll go and try that 

[Erwin83]

Ran the bike at 2000 rpm steadily and released the bolt that stops the tensioner. I can hear that with the bolt undone, the sound changes (tensioner moves) and once I tighten the bolt back down, the sound disappears again.
However, the humming noise while riding has not disappeared.
So, I decided to just take it as it is, and give 'er the beans.

Ride for >30 minutes, oil nice and hot. Sound does not change. Bike runs great.. It is what it is.

[Erwin83]

Reading this article: https://s3.amazonaws.com/sohc4-articles/CB400/Improving_the_CB400F_camchain.pdf
It seems that there actually should be a whine with the chain at normal tension. So I think I'm good.
Again, I've never had a proper tight cam chain in the last 19 years.

[K2-K6]

Sounds like it's working ok. With it's own spring tension it can't over tighten the chain and should just set it.

As that article about chain describes,  it makes a light "tinckling" sound with the chain loose, unlike the tapping from valve clearance that you can seperate with different noise.

They do have a gentle whine/hum when all the adjustment are set correctly. 

[Sesman]

That’s correct Irwin. I recall from my 400/4 days I had to use the screwdriver method to maintain chain tension and restore the original engine noise. Cam chain adjustment became something of an obsession and to be honest it was a relief when I moved the bike on. That engine was pampered. Changing to a bike with a 6k service and auto chain tensioner seemed  like a futuristic transition!