Service

SERVICE

JOE MINTON

All bound up

Help! I own a 1976 Honda CB400F that has been sitting for years, and which I am restoring. The problem is the front disc brake. I’ve replaced the pads, piston and seals, and installed a good-quality used rotor, but upon reassembly, tightening the two caliper bolts resulted in the caliper locking on the rotor. The wheel won’t spin unless I back off the bolts-obviously not a good idea, safety-wise.

I’ve tried the adjustment screw and bled the system, but whenever I tighten the caliper bolts, the brake locks up. Ed Trotta Saint James, New York

There are two areas to check. First, are you sure you 've assembled the caliper correctly? It 's possible to install the caliper piston the wrong way around: The solid end should go into the caliper cavity first.

Another likely cause is that either the rotor or the pads are too thick,

causing binding. I recall that the CB400F had a rather thick rotor, so it is unlikely that an incorrect replacement could be so thick as to create the problem you have described. Standard Honda brake pads shouldn’t

present a problem, either, as they are made to original engineering specifications. A ftermarket pads, on the other hand, could be thicker than stock. You can find pad and rotor dimensions in your Honda shop manual.

What’s this rattle?

I have a 1982 Yamaha Maxim XJ750 with 30,000 miles on its odometer. The bike runs well, but at about 4200 rpm there is a bad rattle in the engine. Do you think it’s my timing chain feeling those 30,000 miles? I currently have the top end torn apart for a valve job.

Robert Frazier Swan Lake, New York

My 28 years of dealing with overhead-cam engines have led me to believe that the most common source of engine rattle is an incompletely controlled cam chain. The chain might be worn unevenly so that there are tight and loose spots as it runs around the sprockets and past the dampers and tensioner. The variations in tension of a running chain with uneven wear can lead to noise. I suggest that you replace the cam chain. While they will certainly last longer than 30,000 miles, this is enough mileage to warrant replacement, especially as you already have the engine apart.

You should check the cam sprockets by wrapping a new chain around them, and then check for looseness between the sprocket and chain links.

The chain should fit very snugly. Your XJ’s cam sprockets may be rather soft.

In the late ’70s and early ’80s, Yamaha made sprockets of sintered steel and their wear rate was high.

A second likely source of noise are the tappets. Tappets rotate as they work and if they and the hole they ride in are out of round, they can rattle.

Check the condition of the cam lobes. Yamaha cams of that period had a tendency to pit on the nose, and this would sometimes set up a rattle, although this minor pitting does not seem to lead to reliability problems.

Don’t knock it

Last winter, I bought a 1983 Kawasaki GPz750 that desperately needed to be rescued from its owner.

The now-healthy Kaw rewarded my efforts with about 7000 miles of trouble-free riding last season. However, a knocking sound from within the engine cases has me worried about the bike’s future reliability.

I had a service manager from the local Kawasaki dealer have a listen.

His diagnosis was that, “The primary chain is slapping. Not to worry, it’s a common problem with these bikes.

Just turn up the idle a bit and the noise will stop.”

I need a second opinion. What can be done, short of replacing what I expect to be a stretched primary chain? Larry Hawks Mt. Clemens, Michigan

The noise you hear probably is the primary chain snatching, not stretching, and likely is a result of carburetors that are out of synchronization. This problem is especially noticeable at idle.

If one of the carburetors is open farther than the others, that cylinder will slow the engine more on its compression stroke because it has more air in it. It will then accelerate its piston more when ignited. This sudden large reversal of load will cause the chain to jerk and snatch, or the gears to rattle against one another.

Careful carburetor synchronization should eliminate most, if not all, of the noise. This is an art as much as it is a science, and having a vacuum-gauge set is not enough to completely qualify a mechanic to do the job. Find an expert. Properly synced, the engine will run more smoothly, be more responsive and stop making noise at idle.

Bum Beemer battery

My 1987 BMW R65 can’t seem to keep its battery charged with all the city riding I do. Will installing a kickstarter solve my problem?

Also, the single front disc brake seems to pull my fork tubes out of alignment. What can I do?

Ken Nason Honolulu, Hawaii

Your BMW needs more energy to start than most four-cylinder engines. Fitting a kickstarter (easily accomplished on your model) would certainly ease the battery ’s lot in life. Stock BMW batteries aren’t the best you can get. If you need a new one, I suggest that you buy a Yuasa Yumicron. It’s been my experience that this model will supply more current for faster starts and will last longer, too.

As for your fork twisting, you need a fork brace. Try a German-made Telefix, available from Spec II (9812 Glen Oaks Blvd., Sun Valley, CA 91352; 818/504-6364). The model you want is FS31, priced at $99. □