A Mechanical Restoration

A Mechanical Restoration story

If you have read my Service page you may remember that I mentioned that “unless your bike was just assembled out of a long lost new bike crate from the factory (and that probably needs work) it has issues relating to safety, performance and appearance”. In this Blog post I am going to describe the complete Mechanical Restoration of a 1974 Honda CB750K4 to illustrate the types of deterioration that happens to old motorcycles that sit for a long time.

This particular machine belongs to the original owner and back in about 1977 he put his bike in the basement rather than take an unreasonably low amount to trade it in on a new bike way back then. The bike had been sitting in the basement for 33 years until he decided it was time to get in fixed up so he could ride it again.

This Old Honda is all original and in very good visual condition except for the aftermarket exhaust. Don’t let that fool you into thinking that there is not much wrong with the bike, there is. When doing the Estimate I found the following. Front tire flat, front brakes seized and fluid dried to crystals, forks seals leaking, steering head bearings notched, no balance weights on wheels, carbs filthy, needs a tune-up, swing arm bushings loose, rear brakes worn, drive chain iffy, handlebar switches intermittent, no battery, rear tire worn, some rust on the frame and engine paint deteriorated from a cracked battery that leaked. I did a compression test which showed the engine was in good condition. I estimated about 14Hrs labour and about $900 for parts during the visual inspection to make it safe to ride. That didn’t include anything I may find when I actually took the bike apart. In the end after adding optional cosmetic work it took 44 hours worth of labor and $1300 worth of parts to return the bike to safe, serviceable and good looking condition and here is why.

The customer approved the work and I began. As soon as I started, things started showing up. After removing the air-box and trying to remove the carbs it quickly became apparent that the rubber intake boots and airbox horns had turned as hard as hockey pucks over the years and it took nearly an hour to carefully pry them off the bike. this should take 5 minutes. The carbs themselves where dirty and corroded on the outside and filthy on the inside. A complete disassembly thorough cleaning and assembly with Keyster carb kits returned them to normal functioning.


When rebuilding the fuel system it is always a good idea to check the fuel tank and petcock for rust and gooop. As I found on this bike. When I removed the fuel petcock I found it full of crap and the rubber parts no longer functioning. After a thorough cleaning and replacing the rubber parts it’s as good as new.


Removing the front brake calliper immediately became a problem as the 2 bolts holding the calliper halves together where seized. I had to carefully pry the whole calliper assembly off the bike and with it clamped in the vice and substantial heat the bolts relented.




While rebuilding the front brakes I discovered the master cylinder piston seized in the bore and it took days of soaking with penetrating oil to release it and careful honing of the bore to get the master cylinder functional and not leaking fluid due to pits from water corrosion.



The calliper piston and brake pad where also seized and required the master cylinder to hydraulically push the piston out after days of penetrating oil soaking. The caliper piston was pitted from water corrosion and was replaced with a stainless steel replacement. That’s why you should be replacing the brake fluid every 2 years.

Brake fluid absorbs water from the air and that water causes lots of problems inside the brake system. The break hoses where also plugged and needed replacing.


The wheels looked fairly good from the outside but when I removed the tire I found lots of rust which must be removed and stopped by painting them before the tire can be installed.



The wheel bearings where also discovered to have big problems. After a thorough cleaning the bearings and seals where found to be serviceable in this case and reinstalled with water proof grease.





The swing arm could be felt to move on the pivot and when it was removed it was obvious that there had never been any grease put through the nipples since the factory shipped it.

After cleaning and measuring the parts they showed within factory specification but without the .002″ of grease between the parts the swing arm could move a lot out at the axle.

This can cause bad things to happen when combined with steering head bearings that have big dents in them. Because these old girls came from the factory with ball bearings in the steering head, not adjusting them so they are loose allows the balls to dent the races and cause bad things to happen in the handling department. I also did some “Optional” work on this bike to improve the appearance.

As a result of years of leaking carbs/battery the paint on the top of the motor was in bad condition so that was masked off and touched up. Because the brake fluid had leaked out and removed the paint on the brake caliper and master cylinder I cleaned up and painted them. The carb bowls and caps where also polished to make them look better as well. With all that done now the frame, swing arm and chain guard looked bad so I painted and touched them up as well.

When I delivered this bike it ran and looked great and will give the owner years of pleasure, if maintained properly.

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