Cb250 Engine Rebuild

Ok, so I didn't have any kerosene or fuel at hand, but I did have a can of WD-40.

So I tried to test the valve seal with it, and i'm not sure of the results.

Sonreir, Ive read through the 'Doing It Right' thread and noted the top end health section.

I see how much fluid got through in the pictures shown and compared it to what I ended up with.

I sprayed quite a bit into the ports one at a time, left it for a few minutes, and came back to inspect. The tiniest amount of fluid got through. It wasn't noticeable until I shined a light on it and saw the glint. It really isn't a lot of fluid at all. (I'll try and get a few pics up in a minute). Is this acceptable, or is any, even the tiniest amount of fluid getting through bad?

[EDIT] - Just looked at the pictures and you literally can't see any fluid so there's no point uploading them.
 
Tiny damp spot will be fine (although a lot of people will say different)
Set intake valve clearance about 0.001" wider than spec, exhausts 0.002" wider and re-check after 100 miles
Valves will burnish seats and should sea; perfect.
The one exhaust valve (in earlier pics where you removed them) was too tight which is why it was completely different colour
 
<b> Long post warning</b>

Ok, achieved a bit today.

I managed to clean all the gunk and stuff off the cylinders, and checked the gasket surface. Seems to be ok with no major indents. Couldn't get all the dirt out from in between the fins but i'm not too bothered about it to be honest.

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Also managed to split the cases.

Pulled the clutch basket and oil pump off, kept the rotor and centrifugal oil filter on the crankshaft.

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Cleaned the oil pump up. Took the screen off and cleaned it out, rinsed in WD40.

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Split the cases open, then pulled the gears out. Some have a very small amount of surface rust on them.

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The gap in the lower case where the end bearing on the gear shaft is has 2 rings on it, but is very smooth with no indents. Is this normal or not?

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Took the crankshaft out the case aswell to check bearing etc.

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Im a bit concerned about surface marking and rust on the crankshaft. All the bearing rotate smoothly and have no play in them, so this is my only worry.

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Thats as far as I got today. Will clean the cases up tomorrow or Christmas day, getting too anxious to get it done and whack it back in the bike!

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I wouldn't worry about any external rust on crank, it's the bearings that will fail if there is even slight rust on the races.
Just put it together and keep an eye out for a crank.
You should bash some dents under back of tank so it fits a bit more level (or raise front?)
Bike looks bent with tank pointing down at front
 
crazypj said:
I wouldn't worry about any external rust on crank, it's the bearings that will fail if there is even slight rust on the races.
Just put it together and keep an eye out for a crank.
You should bash some dents under back of tank so it fits a bit more level (or raise front?)
Bike looks bent with tank pointing down at front

Ok, that eases my mind a bit! Thanks crazypj.

Is that the same for the conrods too? They seem a bit rusty and the top end seems a bit burnt/blackened.

I think I'll check and see what they crankshaft is like in the motor in the bike at the minute, and swap it over if it is better. (This is the spare motor I have)



Yeah, have been considering raising the front up about 1-2 inches (until its level), just want to get it back up and running first!
 
As long as the small end is good no need to worry about things.
Burnt isn't a bad thing, it's just the oil overheated and will prevent rust forming.
The rods are copper plated so the entire thing doesn't get hardened when they are heat trated on bearing surfaces
 
crazypj said:
As long as the small end is good no need to worry about things.
Burnt isn't a bad thing, it's just the oil overheated and will prevent rust forming.
The rods are copper plated so the entire thing doesn't get hardened when they are heat trated on bearing surfaces

Sweet! Small end's seem good, not really sure how to check properly...no signs of extreme wear and they feel smooth so im guessing they are alright.

Again, thanks very much crazypj.
 
Ohhh! Used some oven cleaner to try and tidy up and get all the grime off the cases. Left it off for too long and it ate into the engine finish.

I really wasn't planning on re-spraying the engine, so I can either completely disassemble the engine currently in the bike and use the cases from that as they are much cleaner, or I can use this one as it kind of fits with the 'rustic aged' look I was going for. It could look ok.

<img src="http://imageshack.us/a/img846/1594/23122012541.jpg" alt="Image Hosted by ImageShack.us"/>


Also just checked the shifter forks after a wipedown. They seem to be good with no signs of wear. This bottom end is turning out to be ok.

<img src="http://imageshack.us/a/img12/7715/23122012542.jpg" alt="Image Hosted by ImageShack.us"/>
 
I can't count how many brand new cb250 head gaskets went into the garbage(athena supplies two )I would be tempted to swap cylinder,pistons with cb 350,,,,,,but I don't know if the top case is bored large enough to accept the 350 item..... cb250 was very popular in the UK,,not many made it to NA.................Good Luck
 
Wee Todd said:
I can't count how many brand new cb250 head gaskets went into the garbage(athena supplies two )I would be tempted to swap cylinder,pistons with cb 350,,,,,,but I don't know if the top case is bored large enough to accept the 350 item..... cb250 was very popular in the UK,,not many made it to NA.................Good Luck

I thought the 250 was an almost identical motor to the 360, not the 350?

If the cylinders and pistons would fit, I may look into that swap at a later date, thanks for the encouragement.



Got my new oil seals in, so replaced the ones on the transmission, and will go swap the rest out as I go.
 

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Not done much since the last update.

Took the camshaft out of the other engine I have, and inspected it. Seems to be in a very good usable condition, with no major scoring or pitting on the lobes. Phew! Saved myself some money there so that will be going in the rebuilt engine.

Brought the motor back to university with me to work on in my spare time. A friend of mine who is currently rebuilding a CB500t mentioned someone who does blasting who owes him a few favours. So I may see if I can get my cases and everything blasted and then get them painted up nice and properly. Depends, not too bothered if I cant but If I can get it done reasonably cheap I may aswell.

Also got some Hepolite Chromium plated piston rings ready for the rebuild! :D

Crazypj, I saw your old thread about the oil system mod to the 360. The one where the spring loaded transfer piece inside the clutch cover is grinded and shaped.

How does this help the oiling? Is it to try and fix the poor head oiling issues the cb's have? Could this bike benefit from this?

If it aids in the oiling, I may aswell do it now seeing as everything is apart. Sorry for all the questions! hahah :)
 

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If you do get the cases blasted, try to use soda. Other types of media can get stuck in oil passages and that's never a good thing.
Also, give everything a good wash after it's blasted.
 
Green199 said:
I thought the 250 was an almost identical motor to the 360, not the 350?


There are two variants of 250, the CB350 based one and CB360, completely different motors.
Some countries had capacity limits, it's easier to use same crank with smaller pistons
It was done by Ronald Regan when HD couldn't compete in the 80's, that's why USA had 700cc motors for a few years when everyone else had 750's
 
crazypj said:
There are two variants of 250, the CB350 based one and CB360, completely different motors.
Some countries had capacity limits, it's easier to use same crank with smaller pistons
It was done by Ronald Regan when HD couldn't compete in the 80's, that's why USA had 700cc motors for a few years when everyone else had 750's

Thanks for the info pj. Think the 250k4 is the cb360 variant, as sonrier might have mentioned earlier in the thread. (or maybe somewhere else, been doing so much university work recently I honestly can't think of anything if it isnt related to my work!)

In other news, I got some goodies through! ;D

Picked up some new clutch plates and springs, and nice and cheap BSA T shirt, because, well...why the hell not! hahah
 

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K4 is 350 variant, G5 is 360 variant
Easy to tell which is which, 350 variants have separate cam bearings bolted to sides of head on both sides with chrome covers.
All 360 variants have no removable part on right side and 'finned' alloy points cover
You have 'small' 350, 360 also has an extra bearing on cam (K4 only has bearings on the ends)
 
Sonreir said:
If you do get the cases blasted, try to use soda. Other types of media can get stuck in oil passages and that's never a good thing.
Also, give everything a good wash after it's blasted.

ahh will do sonrier. Thanks for the heads up! :)




crazypj said:
K4 is 350 variant, G5 is 360 variant
Easy to tell which is which, 350 variants have separate cam bearings bolted to sides of head on both sides with chrome covers.
All 360 variants have no removable part on right side and 'finned' alloy points cover
You have 'small' 350, 360 also has an extra bearing on cam (K4 only has bearings on the ends)

ahh my mistake.

Would it be beneficial for me to do the clutch case spring loaded transfer piece mod to help oiling on this motor or not?
 
Yep, the oil transfer piece is slightly different but 350's suffer from cam bearing seizure if used at high rpm.
250 is going to be used at high rpm almost all the time so it's a good mod
 
crazypj said:
K4 is 350 variant, G5 is 360 variant
Easy to tell which is which, 350 variants have separate cam bearings bolted to sides of head on both sides with chrome covers.
All 360 variants have no removable part on right side and 'finned' alloy points cover
You have 'small' 350, 360 also has an extra bearing on cam (K4 only has bearings on the ends)
Also, the CB360/250 based has a gear driven trochoidal oil pump, not a plunger oil pump.
 
mydlyfkryzis said:
Also, the CB360/250 based has a gear driven trochoidal oil pump, not a plunger oil pump.

Thanks for the info man! :)



Not much to report at the minute. Still waiting to see if I can get my cases blasted and cleaned up. Currently studying for University exams that end next monday, so not much will happen til then.

My new endless timing chain came in though, so think I have everything for the rebuild.
 

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