Topic: My First Motorcycle: 1976 CB750F

[Jerry Rxman Griffin aka MuthaF'er]

Looks like another 392 head to me, an oily one at that. Looks like it's been decked previously too. 

[ZingZing]

Fantastic. So does that mean it’s possible that this is the original head? Or would the original 76 head be stamped with a 392? The stamping differences has me confused.

It’s real oily cause I sprayed wd-40 anti-corrosion on everything as I took it apart just to be safe. Better than being sorry I guess  .

[Jerry Rxman Griffin aka MuthaF'er]

Could be original? Possible. The 392 is cast into the heads, not stamped should you see one. No real answer as to why some have, some don't. Probably just different foundries. 

[willbird]

Yes, he has a 76 F which is a F1. The first 392 head appeared in the 75 F. The 'shrouds" by the plug hole from the earlier K's were eliminated and it appears as more of a smooth dished hemi shape but obviously not half round hemi style. It continued to the 76 F and was adopted for the 77 and 78 K engines. Can't say about the A's though? It is not as drastically different as the 77/78 F head with somewhat oval shaped combustion chamber for the big intake valves and the valve angle difference that is blamed for the valve guide wear issue. The 77/78 head came from Honda painted black but any head can be painted black after the fact. Both of my 392 heads are NOW black. The 77/78 F head also has less oil return holes.

Yes the drain back difference is very distinctive, and I have seen K heads billed on Ebay as being the distinctive F type you describe and plainly they are not that.

[ZingZing]

Borrowed a dial indicator and did my best with measuring but my guides and valves are a-ok but I would like to change out the guide seals cause they’re 50 year old rubber.

Can I change my guide seals without removing the guides?

It looks like it’s just held in by circlips but I’ve seen mixed answers some saying you need to remove the guides, and I’m not messing with those.

[willbird]

Borrowed a dial indicator and did my best with measuring but my guides and valves are a-ok but I would like to change out the guide seals cause they’re 50 year old rubber.

Can I change my guide seals without removing the guides?

It looks like it’s just held in by circlips but I’ve seen mixed answers some saying you need to remove the guides, and I’m not messing with those.

The valve seals come off without removing the guides.

[ZingZing]

The valve seals come off without removing the guides.

Shweet, thanks.

[Jerry Rxman Griffin aka MuthaF'er]

Some guys stuff rope into the cylinders to keep the valves from falling into the cylinders. I've heard of others using air pressure?

Good time to replace those weakened 40K mile valve springs too as insurance against one breaking or floating a valve as mine did and destroying the engine.

[ZingZing]

Took a while to for my grease gun to ship but for $6 I can't really complain and it got the brake pistons out.

Looks like a crime scene. Yummy .

Couldn't get any grease through the bleeder valves even after cracking them open a little so I screwed the nozzle into the oil line like others have done, just applying teflon tape to make up for not screwing in the nozzle completely. The rear caliper was a PITA cause only one piston was really stuck so the other came out from the grease real easy but then the grease couldn't build pressure anymore. I tried putting some wood in between the pistons but that didn't work (I used plywood, it crushed it), so I just split the caliper. To build the pressure I needed to seal the brake fluid passage that travels between the halves of the caliper, and holding your finger over it isn't enough (who woulda thought). Instead I threw a wad of teflon tape over the passage and clamped down on it with vise grips effectively sealing the caliper half and allowing the pressure to build behind the piston. I'd think the same would work on the other side of the caliper except you'd need the grease to go through the bleeder valve.

Now I gotta clean these up. What are some methods to clean the calipers up especially the insides where's the seals and piston go? Carpy sells a refurbishing kit (https://carpyscaferacers.com/shop/shop-our-store/motorcycle-parts-accessories/honda-cb500-cb550-cb750-parts-upgrades/brake-caliper-refurbishing-kit/) but that's $22 + shipping for some rubber Dremel wheels. There are other rubber wheels for cheaper that are impregnated with emery that sound good. Also thinking Barkeeper's friend and a cloth wheel on my Dremel (which I already have), Scotchbrite pads, or wire wheel it. Just worried about scratching up the insides too bad.

[ZingZing]

I was planning on re-using my valve springs, they measured in spec and stood up straight (on a very not level ping-pong table). There was some discoloration not sure what it is, maybe corrosion? Grenading my engine doesn't sound like a whole lotta fun.

[ZingZing]

Can anybody identify this exhaust?

https://www.ebay.com/itm/375292291956

Not gonna drop $350 on it but its the same as what came on my bike except the one being sold is shiny and also definetley less holes than mine.

[Jerry Rxman Griffin aka MuthaF'er]

Moving right along.

No wire wheel inside the piston bores

Hope your pistons are not pitted badly. Depends on which side of the seal they are.

Save that square o-ring from the caliper half! Good chance the kits may not have it.

No idea on the exhaust

[RAFster122s]

If you use a wire wheel it needs to be made from brass, not steel coated brass and you gotta keep the rpm down to below 15000 rpm or it starts flinging wires and they are not going to feel good when they puncture your skin or even worse sensitive areas... definitely wear eye protection. The brass will not gouge the soft aluminum

[ZingZing]

No wire wheel inside the piston bores

The brass will not gouge the soft aluminum

I'm sure a brass wire wheel would be fine, I just don't trust myself with power tools so a whole lotta elbow grease it is.

But with that done, the hardest part left is watching my wallet getting lighter. I think I'll have the bike back on the road by the end of July. Can't wait!