Topic: 1972 CB750 O-ring rebuild questions.

[ntm1974]

I did a top to bottom rebuild on my 72 cb750 engine and everything has gone smooth up until this point.  I purchased the o-ring kit from cycle x.

Does this cam journal o-ring size look to be right in the picture 1?

And do I need an o-ring where I am pointing my x-acto knife in picture 2?  It shows it in the schematic but it doesn't seem to go anywhere.   Also, the bike bandit schematic has multiple O-rings listed and I'm not sure which one I need.

Thanks in advance for any guidance.

[lamillertime]

Someone please correct me if I'm wrong, but that o-ring appears to be too large. I had the same problem with a top end kit from cycle-x, not sure if that size is for a later year head or what the deal is. Maybe they will work, but I believe the original size to be smaller. The correct o-ring is #17 in the fische below, part # 91317-300-003



When I went into my local Honda dealer to find them they said that they couldn't get that part # anymore, but they were nice and one of the mechanics gave me four o-rings that would work. I think as long as it fits close to the outside diameter of the oil jet (is this the correct term for this part?) and sits inside the machined recess it will be okay.

Yes, the same size o-ring needs to be placed at that point in your photo under each cam tower, or oil will not be forced properly through the cam towers. The tower oil passages are drilled to be used on the right or left side, so you need to "plug" the side that does not have oil coming into it. If you don't you run the risk of starving the cam bearing surfaces of oil.

[flybox1]

OIL JET O-RING
3.7X1.7MM...and yes, you'll need them in the two 'blank' holes under the cam towers.

they are still available.  I recently bought some.
http://www.cycle-parts.com/Products/1097656-91317-300-003.aspx
http://www.toolpartsdirect.com/cgi-bin/parttools.cgi/91317-300-003
http://www.sell.com/28TC8W

[lamillertime]

Thanks for the additional info flybox, makes you wonder why my local Honda shop couldn't get them.

[iron_worker]

The outside 2 oil passages don't go anywhere but they are the end of the oil path. If oil leaks out from under the cam tower here then the upstream pressure will be too low to lubricate properly (IE the cam bearing surfaces).

IW

[bjbuchanan]

Do put o-ring in the outers, I forgot mine and had to go back and pop them in for peace of mind afterwards

You should be able to use those larger o-rings just fine. The smaller ones would be nicer but the bigger ones work just fine. I personally think that is why they don't do the two different sizes anymore.

I picked up the nitrile rubber -ring pack from harbor freight to supplement/swap for o-rings I prefer the fit of better. Had some viton ones laying around too that I used in hot areas. The generic packs are usually pretty cheap and you can score the exact sizes you need for a relative bargain

[flybox1]

Nitrile and Viton both seal well for our fluids.
Nitrile/Buna-N can withstand up to 250F deg applications.
I use Viton for anything over 200 deg F, and its rated for up to 400 deg F 

[bjbuchanan]

I buy the mobil 1 oil filters off of amazon for cheap in packs of three and they come with nice viton o-rings. Good source for a biton oil pump o-ring rebuild