Topic: Engine case halfs - how to check if they are a pair ?

[mizer]

Hi All,
I'm currently in  the process of rebuilding a CB750 K8.
Engine block was all black and was running ok prior stripping it down.
When is tarted to clean the case i noticed that lower case paint was coming off very easily to the point when i was able to clean it all off, the upper half needed some paint stripper to get it removed.
I also noticed that when cases were matching on the sides, after removing the clutch the upper half was black on the side where the lower wasn't.

This all leads me to be live that this engine might be put together from two different halfs sometime in the past - which is a big NO NO.

Question is - are there any stamp on the halfs, or numbers that could allow me to easily identify that this is a pair or not ?
Most of the bikes have some mold numbers that are matching stamped sometime on the case but i looks and looked on the cases and can't find any clear identification.

Is there any way to tell 100% if the cases are a pair or not ?

[PeWe]

I have had same thought about CB750 cases.

I saw japanese marks and sealer residues inside that made both halves to be connected. Marker pen over both sides.

I also test mounted a crank with plastigage that went well. All bearings equal with expected clearance.
It also rotated smoothly at the 2nd assembly.

[denward17]

Do you think it was factory paint (black) ?  Or a PO job.

You can verify what engine it is by the serial number. Is it a K8 engine?

[Rookster]

There should be matching numbers on both halves at the back of the motor where the breather spigot is.  Usually it is a 3 or 4 digit number stamped into both halves.

Scott

[mizer]

When you refer to numbers - do you mean those ( this is the bottom of the lower half) ?


Here is the case from all angles:

Left side


Right side:


Back:


And insides:


Number:


So you can se that upper half have a completely different colour then lower one - but i tend to blame it on actual paint remover as it covers with area where the previous paint was ( bottom half was not treated with the same ).
Bottom is way more smooth in terms of surface, and when you look at the picture of left side where alternator is - you can see that top half is also smoot in some areas.

Engine was running fine when i bought it and main bearings are also in very good conditions.
The only reason i took it apart is to get that paint of, vapor blast it and refresh teh chrome on the valve cover but now i'm stuck with this and don't really know what to do...

[bryanj]

IF it was running fine with ALL the locating dowels between the halves rebuild it and run it,

[mizer]

Correct - all the dowels were in place when i opened it.
Compression is event at 160 PSI on all cylinders.
I still need to plastigauge the crank with main bearings and rods, if they will be within the service specs i think i'll just blast them, and put together.
Maybe replace 2 gearbox bearings since they are on the way out and that's it ( both chains are within the tolerance and have still some stretch to go ).
Ride it next year or two and see what happens.

[ekpent]

So if I am not mistaken the top case is a 1977 - K7. Was just checking to see what numbers the 77-78 F models with the black engines had since you were describing stubborn black paint. http://www.hondachopper.com/engine/engine_timeline/timeline.html

[Don R]

 If it had good bearings when you took it apart, I'd go with it. Bearing match would have been the concern if it were mixed.

[PeWe]

Is one case glass beaded?
If it is look for repairs on that case. The other has harder sitting paint?

[Rookster]

Maybe the numbers were only on the earlier cases.  Here is a picture of a set of K1 cases with a matching number (Z956) stamped into each half at the rear of the cases by the breather spigot.



Scott

[denward17]

^I don't remember seeing stamped #s like that on my K8 when it was out of the frame.

[PeWe]

My CB750 K 1975 cases have no numbers at rear.

They have for me matching graphitti inside.

[CycleRanger]

This was inside my K3 engine.

[dave500]

id replace the chains seeing its apart?if you decide to sell it later on its a selling point?