Topic: Early 750 cylinder head oilways

[Tim2005]

I'm considering building an 836 motor & been having a search through my parts stocks. I found an early type head which appears to have been rather nicely gas flowed (I was pretty surprised to discover I have this!), although it does need a good clean, some fin repairs, several helicoils and a gentle skimming too. Then I just need to find some valves, cut them in and it should be good to go. 

However, comparing it to other heads the oilway restricter jet, circled in red in the photo, is different to all the later heads I have, It does not seem to be a removeable jet like they have. Is this a standard feature, or someone's modification, and is it actually removeable for cleaning the oilways?

Also there are no oil seals on the exhaust valve guides; is that correct?   

Thanks

[nokrome]

what year is that head from?
  i have a 71 and a 72 and they both have the removable oil restricter
   

[754]

 Looks like a K0 head, no center bolt on the front.

 I may be wrong on this but on the removable jet ones, it may be easier to insure its clean passage after a mishap..?

[Tim2005]

Ah, so it's not removeable then, that's a shame as the head is pretty filthy. I'll try to syringe some petrol through there at least.

Here's a better pic of the whole head, with a later (removeable oil jet) head above it so you can perhaps see what model it's off. I can't spot any different center bolt, where should I be looking?

Also, I notice that the exhaust valve guides are not shaped to ever have a seal on them.

[MRieck]

Ah, so it's not removeable then, that's a shame as the head is pretty filthy. I'll try to syringe some petrol through there at least.

Here's a better pic of the whole head, with a later (removeable oil jet) head above it so you can perhaps see what model it's off. I can't spot any different center bolt, where should I be looking?

Also, I notice that the exhaust valve guides are not shaped to ever have a seal on them.

Those oil restrictors sometimes fall out after heating the head and banging the guides out. They look like a bowl shaped strainer underneath. Blast brake cleaner through the top hole and hit with air. You should see the real early oil feeds. Replace the exhaust guides with some that use the oil seal.

[Tim2005]

Thanks Mike. With the current temperature in my workshop they aren't likely to move at all then, it's about 10 degrees f here tonight. I'll give them a good rinse & blast as you suggest when it warms up.   

What's the reasoning behind changing the guides (though I have not yet checked them for wear so may have to anyway)? The 400/4 does not have any seals on the exhaust guides & I haven't found that it causes any problems, indeed my current commuter 400/4 engine has ridiculously low oil consumption.

Thanks

[MCRider]

Thanks Mike. With the current temperature in my workshop they aren't likely to move at all then, it's about 10 degrees f here tonight. I'll give them a good rinse & blast as you suggest when it warms up.   

What's the reasoning behind changing the guides (though I have not yet checked them for wear so may have to anyway)? The 400/4 does not have any seals on the exhaust guides & I haven't found that it causes any problems, indeed my current commuter 400/4 engine has ridiculously low oil consumption.

Thanks

As many have stated, you just have an early head. Clean the orifices with wire and the rest and it will be fine in my opinion. The exhaust guides went without seals on the early ones for reasons you have mentioned, other bikes don't have them. And they rob horsepower. So Honda thought they could get away with just intake seals as that's where the most obvious sucking situation occurs.

However it was found that without them the mighty CB750 would smoke a little and as EPA regs were tightening up so voila, exhaust seals appeared. (same as the intake seal).

I'm going to run sans seals on my project. I may be sorry, we'll see.

[MRieck]

 The early exhaust guides are a problem with high lift cams. The guides are very tall (to keep them above the oil). Many Honda have run no seals....CB350, 400 etc etc. The seal really controls oil well and allows the use of any cam.

[MCRider]

The early exhaust guides are a problem with high lift cams. The guides are very tall (to keep them above the oil). Many Honda have run no seals....CB350, 400 etc etc. The seal really controls oil well and allows the use of any cam.

I didn't know that. I'll have to check my lift. Pretty puny cam, but still...  Thanks.