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Noise doctor needed - mice in the engine or transmission

Submitted by tom_mortensen on Tue, 21/08/2012
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Commando

Over time my 1972 Roadster has developed a very strange noise. It's a high pitched squeaky sound, like a bunch of mice on the loose. The noise comes from the engine / transmission area. First I thought it was the rear chain, which was well an truly clapped out. So I fitted a completely new chain and sprocket kit. No luck, mice still having a party!

Having tried to tune in on the source of the noise, I have noticed that it's closely load related. During engine braking, or neutral load, i.e. no accelleration, the sound is absent. As soon as I wind the throttle open, the mice open their mouths too! The harder and more abruptly I open the throttle, the higher the noise.

Now I'm thinking engine, valves, cam chain, etc.. On my Matchless, sqeaking sounds from the engine means dry inlet valve guides, could this be the same on the Commando engine? If so, how do I cure it?

Any other ideas most welcome, since first of all I don't like that sound, and I can't help thinking it might not be healthy either !?!?

Submitted by tom_mortensen on Thu, 23/08/2012

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Valid points all of them, I will check in order of convenience. Now that the head gasket is mentioned, I have experienced this on other engines as well, with whisteling and hissing sounds, so who knows.... Will report back.

Submitted by dave_graham1 on Wed, 03/10/2012

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I had a similar problem with my 72 Commando. I don't know if your noise is the same, but minesqueakedin time with the revs as if it was a squeaky bed spring. It started doing it when it got warm but was ok when cold. Then got worse and worse. I got the bike hot so it was squeaking, then took the plugs out and turned the engine over slowly by hand using the kick start. I could hear the sound coming from the timing side.

The problem was the replacement bushes used on the cam. Instead of 1 bush, this is nowsuperseded with the 2 top hat bushes 06-5428 as fitted to the MkIII, which leaves a gap in the middle. These 2 bushes were spinning in the casing as there isn't enough surface area to hold them firm. I could also see from the scuffed up area on the outside of these bushes that only half of the surface was actually touching the crankcase, as if the bushes weren'tparallel.

Also I found out that these bushes have been known to cause problems in pre MkIII crankcases, being too tight against the cam.

Here's some info from Old Brits website.http://www.oldbritts.com/cam_bush.html

Although Andover Norton offer the 2 bushes as a replacement, the drive side cam bush isexactlythe same as the original timing side bush 06-2600. I fitted this in the timing side and the problem was solved.

I hope this helps, if not, maybe turning the engine over slowly will help identify where the squeak is coming from.

Submitted by tom_mortensen on Tue, 09/10/2012

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Status right now: an attempt to locate where the sound originates from has pointed me in direction of the cylinder head. Before that I checked the timing chain, bratherand the exhaust pipes. No luck. The cylinder head or what's inside are now the primary supects. I have noticed that there is the an ever so slight oil leak between the cylinder head and cylinder, just above the left hand exhaust pipe. So a tiny gasket lead could be the answer although I cannot locate the sound to this specific area, but then again noises are difficult to trace.

So next step will be taking the head off, which will give me an opportunity to check valves, guides and cam bushes as suggested. I will report back on my findings.

I'm just holding it a bit, trying to get some riding days out of October, but lately its getting bloody cold!

Submitted by tom_mortensen on Mon, 15/10/2012

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Ok, problem solved! Friday going to work, upon arrival afteran 8 miles motorway blast, my left boot andleft side of the machine was covered in oil. Inspected the outside of the engine closely, but couldn't really find the leak, although a major part of the oil seemed to originate from "some place" on top of the rockerbox. All nuts tight and no crack anywhere. On the way home, on the motorwaydoing about 80, Ibentdown to look at the top of the engine(yeah I know, but not a lot of traffic!). Oil seemedto run down from the top of the rockerbox, then gather in a pool at the smallcooling fin behind theexhaust andthen blasted sideways towards the back of the bike,coveringeverything in the way with oil. Reduced speed and limped home.

Petrol tank off, nothing visible, butoil definitely comingfrom the rockerbox. I then ran my finger along the rocker feed oil line, the one connecting left and right side of rockerbox. And there I felt it, thetransparent plasticoil line, hardened over the years,had cracked allowing oil to escape. Fortunately I had on the shelf a complete set of braided rocker feed oil lines from Norvil, bought earlier with the intention of getting rid of the ugly plastic tubing. Once fitted, I let the engine idle for a bit, checked that oil was actually fed to the rockers and went for a ride. Revelation: Both the pesky little mice and the clatter, earlier diagnosed as either cam follower wear or piston slap had gone! Excellent result for a simple and quick repair, killing a couple of birds with one stone!

Thanks for all the suggestions!

Submitted by tom_mortensen on Wed, 17/10/2012

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Yes, only time will tell whether that is the case. But so far, about 100 miles later, no ill effects, the topend has become significantly quieter. I have made a mental note though, of the possible pitfalls in replacing the cam bushes.

 


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