Topic: Calling all CB750 DOHC gurus!

[750mors]

Ladies and Gentlemen,

I am in desperate need of knowledge deeper than mine, I am nearing the rolling point of my cafe build on a 1982 CB750 DOHC and have hit a road block.

I was diligently following the instructions for the engine rebuild and noticed one part which I can't account for "oil control orifice" part number 11620-425-003 (part obsolete). There is almost zero info on this part worldwide and I want to continue the tradition of building the bike right so any info that anyone can share would be much appreciated.

Below is a picture of my lower crankcase, I don't know exactly where the orifice would fit. There's also the possibility that I may have jumped the gun though which is my I'm hoping to find an expert eye - is the part already in the gallery toward the top of the picture??? I have also included the microfiche too, it's part number 21.


Thanks in advance for taking the time to read, anything that can be added to the topic will be greatly appreciated.

Matt

[750mors]

[Retro Rocket]

Is that it in the hole next to your primary chain in the top picture, the white plug..?  Did you remove and replace that ? It looks like it just blocks off an oil gallery internally, if you haven't pulled it out then i wouldn't touch it......

[750mors]

Hey retro,
How I ended up in this spot is that I didn't ever remove it and don't recall seeing it. But the guy that did the Vapour blasting for me did remove some bits and pieces which I didn't have time to remove. He claims to have not removed it either... So now I'm just completely unsure about it all.

If it is the white plug that you mentioned I can't see how it would do it's job as an oil control orifice as there appears to be no passage through to the upper crankcase. I haven't had it out and won't be removing it. But I'm quite worried about missing a key piece of the build here...

[calj737]

Looking at the parts fiche, it appears that part 21 has a perforated stem, to control oil flow rate, not prevent it. Is it possible the plug Retro and you are discussing actually has small opening that does allow oil to pass, and you can't see it from that vantage point?

[750mors]

That could be possible calj, if it was controlling the flow into a side port that would make sense. It will most likely lead me to removing the plug in question to a least see what I'm dealing with.

[Retro Rocket]

Sounds like you need to talk to a mechanic that knows these engines, I had a 750 and 900 boldor but never went inside the engines...
If that hole with the white plug in it isn't an oil gallery, then i have no idea why it would be plugged, look under the engine where that gallery {or what ever it is} would go and see if it looks like a gallery, the other alternative is to carefully pull it out and see for yourself. It does look similar to the part 21 in the diagram. Sorry i can't be of more help..

[750mors]

Thanks retro, it all helps. I'm hoping someone with the mentioned know-how can chime in. Otherwise I'll just have to hit the streets and start asking the local bike shops.
Matt

[Retro Rocket]

Try this place...

http://www.cb750c.com/

[750mors]

Cheers Retro, have just posted over there so hopefully someone will know something.

Matt

[MRieck]

I haven't been inside a DOHC in quite a while but I am sure it goes in the stepped hole at the top of the pic. The oil control piece looks exactly like the the pieces used in later model SOHC heads (under the cam towers). I have spares of those if it is the part.

[750mors]

Thanks for the lead MRieck, will keep digging into it. I'll check out the SOHCs too to see what they have. Would it be possible for you to share a pic of the pieces you have when you find the time?
Matt


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[MRieck]

Thanks for the lead MRieck, will keep digging into it. I'll check out the SOHCs too to see what they have. Would it be possible for you to share a pic of the pieces you have when you find the time?
Matt


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I'll get a pic up today

[MRieck]

Here you go

[750mors]

Thank you a thousand times!! That should surely help me through! LEGEND!


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[Bill/BentON Racing]

My thoughts also, got a part number, looks like std 750 one, Bill