Topic: Oil Control to the top end

[H2Eric]

Hi folks

Beneath the cam carriers on the CB750 there lurks what Mr Honda calls the 'Oil Control Orifice' (part No. 12238-300-010) that sits in the cylinder head. Unfortunately they've gone missing. I took them out before sending the head to be gas flowed and obviously put them in a safe place, so safe in fact they can't be found. As these parts are no longer available from Mr. H is it acceptable to run without these or am I courting disaster if I do?

Cheers
Eric

[ekpent]

Better keep looking as I am sure they serve a very important function. Smarter people than me will chime in but they probably deal with pressure and flow to the important top end.

[wrenchmuch]

Without them you'll starve your main and rod bearings for oil especially when the oil gets hot .

[Bodi]

Absolutely needed. You could have some made by a machinist - you just need a sample or someone to measure one. Outside diameter, length, and the profile of the orifice itself (actual orifice diameter and the depth of the bores to it on either side or the thickness of the smaller section with the orifice hole).
Or someone here with a collection of parts motors may send you a pair.

[mycb750k6]

What bike, year. I think they changed some over the years. You could buy a head from salvage. That might be an inexpensive option. They are pretty hard to get out aren't they? They have an oil ring on top of them don't they? Do you have those?

[H2Eric]

What bike, year. I think they changed some over the years. You could buy a head from salvage. That might be an inexpensive option. They are pretty hard to get out aren't they? They have an oil ring on top of them don't they? Do you have those?

I thought that they might be important, I guess that without them the oil pressure to main bearings is going to drop somewhat with non too pleasent consequences. I have the 'O' rings that go on the top. As for the year of the engine, the crankcases are from a K4, but I haven't a clue what the rest came from as its been put together from a heap of spare parts left over from a race bike I had years ago. I checked the oil control orifice on anther engine, they wouldn't come out of course, but at least I could measure the tiny hole in the centre, so I've tried to make one today. Took three attempts and two broken drills. The tiny hole in the centre is only 0.8mm diameter hence the broken drills and a few choice words! The finished article is a slightly sloppy fit in the cylinder head, so unless anyone can come up with a pair of these things I'll attempt a Mk IV when I have the patience and some more tiny drills.

Thanks
Eric