Ever changed balancer chain on Honda Twin 400-450?

[sono]

Hi,
I would like to know if any of you ever did perform a balancer chain change on a Honda Twin such as CB400-450, CB450SC Nighthawk, CM400-450.

I've got a CM400T 1980 but I had a bad surprise yesterday: the balancer chain keeps being noisy despite recommended adjustment and it appears to be at service limit (must replace the balancer chain if still noisy when wear indicator on balancer shaft is up to 3 o'clock) it cannot be adjusted any further. The user's manual recommends to adjust it only if noisy and specifies it should be checked after 10,000km. I suspect it has simply never been adjusted and worn out prematurely. Who reads the user's manual ? I do.

The service manual suggest to remove the head and cylinder first, but is it essential ?  Any bearing or worn glider will be changed.

PROBLEM: I'm just reluctant to dismantle the top of the engine because engine head and piston rings have just been restored to specs. DO I ABSOLUTELY NEED TO TAKE IT APART ? It would be cumbersome, but I don't think is it essential. As we say, "If they are not broken, don't fix it !"

I've got all required parts and Service manual. If I'm lucky, only the balancer chain and gliders will need replacement. I may replace timing chain to be on the safe side, as well as any worn bearing and oil seals I may find.

If any of you ever did such repair I would lile to have an opinion on how many hours it represents ?  My mechanic is talking of 12 hour... He was telling me that balancer chain adjustment took 3 hours and I did it in less than two (I'm not a mechanic, but I am quite handy with tools and a manual).

Thanks if you can help to keep my 28years old motorcycle in good health.  

I'm actually considering buying a spare engine or even a spare bike for parts, so that I don't risk to damage my rebuilt engine if the the balancer chain beaks. It is only doing noise at 5-6000rpm, which is my cruising speed (90-100 km/h). I would ride on the spare engine this summer and fix mine in the meantime.

[Searchguru]

Hi,
I've replaced cam and balancer chains on both CB250T (Dream) and CB250N (Super Dream). New chains, tensioners and I remember that there were a number of baby cush-drive rubbers in the balancer weights. I used a Haynes manual to learn how to do the Dream and it took an age because of my inexperience. I did the Super Dream about 6 months later and it was a breeze. The only trouble is that this was in 1983 so I can't remember specifics. I do know that the original task was to replace the cam chain adjuster which led onto the balancer weight rubbers etc. and ultimately to both chains being replaced. 12 hours for a professional mechanic sounds like he might be planning a 6 hour lunch break! Are your crankcases split horizontally or vertically? If they are horizontal (I can't remember what the Dreams were) then it is possible that you could split the cases to get at the balancer parts. Have a go yourself and take your time, it will be very satisfying once you get it right.

I've just had a moment of clarity. This is difficult to explain but worth a try before you take it all apart. I remember that the the adjuster was held on a spline at the end of the shaft with a 10mm nut. The adjuster had a slot in it that the shaft of a pinch bolt ran through and into the alloy casing. Try removing the 10mm nut then the adjustment bolt. See if you can remove the adjuster from the spline and move it around a couple of teeth, then readjust. A bit like adjusting your gear change lever. If your bike is the same, it might take up the slack, you never know.

[sono]

Dear SearchGuru...
I've got the Clymer Service manual and I've read the procedure over and over.

I'm glad you think an estimate of 12 hour is too much, I've got a second estimate a 6-7 hours today, which makes more sense to me. The model I have (CM400 1980) is splitting on the bottom, so sides do not even need to be removed. The balancer tensionner assembly is directly accessible once the case is split.

As for my second question, I still don't feel like removing the engine head, but I may if I have to, because I need to remove the camshaft to change the timing chain. Once Camshaft rockers are removed, there is nothing left to hold the engine together.  If I am working in a clean environment an properly idenfity R an L side parts, I should be OK. I know pistons and rings are fine, I want to keep it that way.

As it is explained in the service manual, the balancer chain must be changed once the wear indicator tells you to. They explain engine vibrations at high RPM are increasing because the balancer are getting out of sync once the chain is stretched beyond the wear indicator mark.  If I try adjusting the tension further, chain noise may stop, but engine vibration will get much worse, as chances of snapping the worn chain into a running engine...  I cannot take such chance, now that compression is restored to specs, engine head is back like new and it is not burning a drop of oil anymore.

Your little story on a similar twin is boosting my confidence and it tells me I can probably do it within a day or two. My main concern is to open and find other damaged parts I must replace and wait for. I've already purchased the rare parts that must be replaced no matter what (such as chains, gliders, new connecting rod bolts). Once the case is split, I will be able to tell and I already located vendors that carry all extra parts I may need, shipped within two weeks to Canada.

To avoir part backorder delays and to risk breaking my engine before I can fix it at the end of season (I'm riding 12,000km/year), I'm planning to buy and install a spare engine and swap it whenever necessary for major repairs.  I know, I will wear them both eventually !!! I'm targeting CM450 or CB450 engines which have an automatic balancer chain instead of CM400 which requires to remove the side cover every second manual adjustment.

You see, I've got my plan, but thanks to you and a comple of buddies I will dare to take my engine apart... knowing I've got a spare one too !

Thanks again

Sono

[Searchguru]

Sono,
It sounds like you have put a lot of thought into it but as they say in military circles "A plan never survives first contact".
Don't forget a picture paints a thousand words. Take photos when it starts getting tricky then you'll have a better idea what goes where for the rebuild.
Good luck Tony B.