Topic: 1972 CB500 1st build but not last for sure

[Jeremy28c]

Well a guy at work gave me three motorcycles and this 72 cb500 is going to be my first build. I bought a 78 cb750f that was already tore apart and started but since I wasn't the one that tore it down I was thinking I would get the 500 going first. The reason it has sat for the last 15 years was the previous owner said the oil light started coming on so he changed the oil. It would stay on at idle but if you hit the throttle it would go off. I bought a used oil pump, sender, o-rings to pull the oil pump out and check it then put that all back together. I pulled the carbs off and they were as suspected all gummed up, so I'll be sending those of the get cleaned and rebuilt. My question is about the lower end. I am going to pull the head and cylinder and at least put new pistons and rings in. With this motor having 43k miles and only knowing what the last owner said what are your guys opinion about pulling the bottom end apart. To be honest the bearing sizes do confuse me alittle. I also would have to get all new rod bolts and nuts. I can find the bolts ($15ea) but haven't found the nuts yet. I think I know what I should do but would love to hear some other opinions on what you guys would do. Thanks  More Pictures to Come

[calj737]

New rod bolts and nuts are not necessary. If you do split the cases, it's a good idea to replace the primary and cam chains.

Beatings are indicated by an alphabetic code on the lower case, rear. The stamped letters correspond to size and "color" found in the manual. I doubt they are damaged or worn unless there's been oil starvation or abuse.

Possibly just a hone of the cylinders and new rings is all you'll need to get the motor rolling again "good as new". Once apart, measure the bores and pistons to verify wear tolerances. Rings are inexpensive for the stock piston and are a good values or reliability.

Sounds like the ground or switch itself was bad on the oil pressure unit. Not uncommon on a. 40 year old bike.

[Stev-o]

Welcome Jer.  CB500 are good bikes, I had one.

If not too late, I would suggest getting the bike running then determine the need of a top end and tranny work. These bikes, if properly maintained [tune ups and oil changes] are known to go 50K miles or more with out a rebuild.

[rickmoore24]

Welcome!! I second the hone and re-ring route, unless your're having trans issues, I'd avoid splitting the cases. Good luck!

[Jeremy28c]

I checked the compression and number 3 was only about 40lbs. The rest were all 100-125 thats why Im thinking just top end if I can get by with it. The carbs are so bad I dought it would even start.

[Stev-o]

A good cleaning/rebuild of the carbs is a must. 

[rb550four]

You may just have a sticky valve on #3 not seatingproperly or the gauge wasn't seated properly.
I'd do the compression check again to be sure.
 Of course there is always a chance of blow by with broken rings too. If the test came out the same next time I think it would be time to take the top end down and find out why.