Topic: need price info for partial rebuild of engine

[pbelanger]

Hi,

My 1976 CB750K has some oil leaking on cylinder one, I suspect at the joint between the head and the cylinder block. Also, at hi revs, let's say, around 5000 rpm and more, it burns oil a bit, because I see blue smoke coming out of the exhaust. 32 000 miles on the bike.

Questions:

(1) What could be the problem? Simple job of changing the rings on the pitons?

(2) If I go for a partial rebuild job e.g., new set of rings on the 4 pistons, will it be enough? Must I also go for a crank bearings job, cam bearings, the whole works?

(3) What is your estimate for such a job? (rings) Time + price estimate would be greatly appreciated.

I don't have the space to do this, so I will have to bring the bike to a mechanic and I don't want to get screwed for part$$$ and labor. (I live in Montreal, prov. of Quebec, Canada)


Thanks in advance for your responses,

Paul

CB750K 1976

[ProTeal55]

Check out---->
http://www.cyclexchange.net/
They do more than their share of motor rebuilds/upgrades...

[bryanj]

Bottom end would be expected to be OK but at 32,000 and the age i would say you need:-

(1) valve stem seals with valve clean up

(2) Cam chain C/W ALL the rubber tensioners

(3) Complete gasket and seal kit

with the possibility of

(1) Piston rings plus hone

(2) primary chains

If given the engine only i would expect to complete the job in 5-6 hours assuming all the parts are immediately to hand

[Bob Wessner]

i would expect to complete the job in 5-6 hours

Hmm, I could spend twice that amount of time just thinking about what to do. 

[scunny]

also to be considered when rebuilding the motor yourself is the cost of beer. 4to6 hours gazing at said motor, then more beer. mmmmmm expensive.

[bryanj]

Dont forget Bob that time is AFTER the engine is out and on a BIG clean bench with all the tools and parts to hand, Plus the fact i used to do, shall we say, a few!

[crazypj]

Take it out and give it a good revving. 5,000 rpm is LOW for this motor. the bores are probably glazed through being under used. If your rebuilding it anyway you have nothing to lose (except maybe a speeding ticket) you'll also get some idea of how they were designed to be ridden.
PJ

[Clyde]

I would go with what Brian suggests. The 750 engines have to be pulled out of the frame to do anything serious on and you do not want to do that too often.
I would measure the play in the primary chains as Honda recommends. 65mm is about right for a new set of chains and the limit is 70mm. I change if above 68mm. This can be checked whilst the engine is in the bike. I would replace the primary chain tensionser regardless.
Honda cylinders are very hard and normally do not wear much. It is common practice to give a light hone and fit a new set of rings.
Given the age and I presume that it has not been pulled down before, I would also replace all the seals as suggested. Especially the 6(six) 'button seals' between the cam towers and the head, as that is probably where your leak is coming from. The oil runs down onto the joint between the head and the cylinder. It could be the head gasket, but they normally just weep a bit.
Regds Clyde

[MRieck]

FYI...There are no cam bearings in a CB750.