Topic: Cb750 k2 burning oil from cylinder 4

[Phoenix]

In this long conversation, nothing has been mentioned about removing the engine for a top-end job.  There are frame-cut kits out there that make top-end jobs in situ do able.  But get the one that you can weld back to original if you want.
Also, cylander bore was mentioned.  I got into a big fight with a local engine guy with regard to clearance.  Hondaman and Mike R. are the gospel on this.

[Medyo Bastos]

back in the 1900’s i remember rotating an engine forward to pull top end off without pulling the engine out.


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[scottly]

It's only burning oil in one cylinder, so one would assume that the bore clearances would be the same for all 4 jugs?
Since the bike was purchased from the guy who rebuilt the motor, I would take it back to him and see if he will make it right. He obviously screwed something up.

[RacingSaints]

In this long conversation, nothing has been mentioned about removing the engine for a top-end job.  There are frame-cut kits out there that make top-end jobs in situ do able.  But get the one that you can weld back to original if you want.
Also, cylander bore was mentioned.  I got into a big fight with a local engine guy with regard to clearance.  Hondaman and Mike R. are the gospel on this.

Got it okok, I think id prefer pulling the engine rather then cutting the frame, also i was talking to the PO and he said if I couldn't figure it i could drop the bike over to his place again and he'd take a look. 

[RacingSaints]

back in the 1900’s i remember rotating an engine forward to pull top end off without pulling the engine out.


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Interesting...

[RacingSaints]

It's only burning oil in one cylinder, so one would assume that the bore clearances would be the same for all 4 jugs?
Since the bike was purchased from the guy who rebuilt the motor, I would take it back to him and see if he will make it right. He obviously screwed something up.

Yeah thats exactly what Im thinking

[HondaMan]

back in the 1900’s i remember rotating an engine forward to pull top end off without pulling the engine out.


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Did you work in my roadracing crew?

[HondaMan]

What is the serial number on that engine, and the build date on the label attached to the steering tree?
Reason I ask: builds made before 4/1972 had engines with Stellite valve guides, which last over 100,000 miles. The ones made after that have cast-iron valve quides which can wear quickly if the bike was parked (and not prepped for storage) for a long time. Those later guides get rust in them while parked, and if not carefully restarted (as in, valve removed, guides cleaned and stem polished again) they can end up with too much clearance, and then leak oil. The exhaust guides made before 4/1972 are distinctive: they have no valve seals, nor a groove to hold one.

Ask your friend expressly: what piston-to-bore clearance was used in the "rebuild".

Hmm okok, I'll try to get that info. I do have a picture of the little label.

That's just a month after the 'official' stoppage of the Stellite guides, but I have seen an occasional engine (like K3 and K4) that had a head with the Stellite guides. This would happen because Honda might find something deficient in their inspection of the engine post-build, and the engine (or parts of it) would be removed back to the stage where the defect could be corrected, then it would get re-inspected and go back to the production line. This was (and is, in these bikes) VERY common. As a single point-of-knowing in my own 750K2 (build date 11/71 on the headstock) is: my engine is/was a reworked early K1 (very early) with the 6-plate clutch and the 2 wires in the clutch hub that held the 2 inner plates still (the K0 Old Factory engines had these, too) and in 1980 when I took it down (my post-racing years) when I optimized it more for heavy 2-up touring I found the K0-style final-drive bearings with the retainer ring and groove in them - so, it was/is a much-reworked K0 or K1 style engine that ended up in a K2 frame after wandering around the factory for some time!

[RacingSaints]

That pic is the frame/vin number, the engine number is on a rectangulsr pad on the top crankcase and will be different, the engine number is what Mark needs

I cant seem to find that sticker, would I need to take the tank off to see it?

[scottly]

It's not a sticker, the numbers are stamped into the crankcase on the left side. Besides, it's a moot point, as you are going to take the bike back to the guy that rebuilt it. Keep us posted.

[RacingSaints]

It's not a sticker, the numbers are stamped into the crankcase on the left side. Besides, it's a moot point, as you are going to take the bike back to the guy that rebuilt it. Keep us posted.

Ahh okay got it.
And yeah I'll let u guys know what becomes of it. The guy that rebuild it is out of town until Sept so I'll have to wait a couple weeks but yeah. Anywyas you guys have been awesome thank you all so so much

[RacingSaints]

What is the serial number on that engine, and the build date on the label attached to the steering tree?
Reason I ask: builds made before 4/1972 had engines with Stellite valve guides, which last over 100,000 miles. The ones made after that have cast-iron valve quides which can wear quickly if the bike was parked (and not prepped for storage) for a long time. Those later guides get rust in them while parked, and if not carefully restarted (as in, valve removed, guides cleaned and stem polished again) they can end up with too much clearance, and then leak oil. The exhaust guides made before 4/1972 are distinctive: they have no valve seals, nor a groove to hold one.

Ask your friend expressly: what piston-to-bore clearance was used in the "rebuild".

Hmm okok, I'll try to get that info. I do have a picture of the little label.

That's just a month after the 'official' stoppage of the Stellite guides, but I have seen an occasional engine (like K3 and K4) that had a head with the Stellite guides. This would happen because Honda might find something deficient in their inspection of the engine post-build, and the engine (or parts of it) would be removed back to the stage where the defect could be corrected, then it would get re-inspected and go back to the production line. This was (and is, in these bikes) VERY common. As a single point-of-knowing in my own 750K2 (build date 11/71 on the headstock) is: my engine is/was a reworked early K1 (very early) with the 6-plate clutch and the 2 wires in the clutch hub that held the 2 inner plates still (the K0 Old Factory engines had these, too) and in 1980 when I took it down (my post-racing years) when I optimized it more for heavy 2-up touring I found the K0-style final-drive bearings with the retainer ring and groove in them - so, it was/is a much-reworked K0 or K1 style engine that ended up in a K2 frame after wandering around the factory for some time!

Thats pretty cool, think I might be lucky and have those satellite valve guides on mine too?

[RacingSaints]

Also totally not important by any means but just because I think they look cool, here are some pics of the bike

[MRieck]

Exhaust guides with seals always use less oil.....That's why Honda went with that design. Basically every motorcycle engine over the last 50 years uses exhaust guide seals.

[newday777]

Also totally not important by any means but just because I think they look cool, here are some pics of the bike

Yup, not only cool either,  lots of fun to ride a bike that has soul.

[RacingSaints]

Also totally not important by any means but just because I think they look cool, here are some pics of the bike

Yup, not only cool either,  lots of fun to ride a bike that has soul.

Yeah that's for sure! I love that bike, it makes me feel like I'm on a real machine. Absolutely amazing. My buddies will always laugh saying I'm the youngest one (18) and I got the oldest bike out of all of them. 

[newday777]

Also totally not important by any means but just because I think they look cool, here are some pics of the bike

Yup, not only cool either,  lots of fun to ride a bike that has soul.

Yeah that's for sure! I love that bike, it makes me feel like I'm on a real machine. Absolutely amazing. My buddies will always laugh saying I'm the youngest one (18) and I got the oldest bike out of all of them.

😎👍

[RacingSaints]

Just an update, got the bike back the other day. It turned out to be an oil scraper ring that broke... also wrecked the cylinder. The PO was super nice and had another engine in his shop that was fully rebuild and ready to go and he installed that for me as fixing the old one would take longer and I wanted to ride this season. But yeah anyways, my cb750 is up and running again! Thank you all for the help!

Attached are some pictures the PO sent me of my old engine

[scottly]

You can have good compression if the top piston rings are good, but high oil consumption and smoke if the oil ring is bad; one piece oil rings can break, and 3 piece rings can be miss-assembled rather easily.

The PO sounds like a stand-up kind of guy.

[bryanj]

Looks more to me like the circlip came out but he sounds a good guy so it dont matter

[MRieck]

Looks more to me like the circlip came out but he sounds a good guy so it dont matter

Exactly

[RacingSaints]

You can have good compression if the top piston rings are good, but high oil consumption and smoke if the oil ring is bad; one piece oil rings can break, and 3 piece rings can be miss-assembled rather easily.

The PO sounds like a stand-up kind of guy.

He's a super awesome dude for sure! He also told me I could bring it by in the spring next season and he'd give it a tune up. Wouldn't take any money, just said "now I can sleep at night knowing your bike is running good" 
Definitely got really lucky with where I bought my bike. He's also the one who told me about this forum  

[newday777]

Good to hear that it is fixed and you are back on the road

[bryanj]

This guy is one to keep in touch with, way more honest than most sellers and worth his weight in gold

[lash]

Late to  the party but some further info.
So it appears that a circlip broke and did the damage. First time that has happened after doing more than a few engines.