Topic: Cb750f2 engine rebuild

[Stev-o]

I’m fortunate enough to be in a spot where I can build my CB out to be a fun unique machine and glad to get a head built as the foundation of making this motor performing!

It has been my experience that a rebuilt head is key to having a great running motor.

[grcamna2]

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[CB750R]

It has been my experience that a rebuilt head is key to having a great running motor.

Yes I’ve been a long time lurker on this site, have read a lot of positive testimonials about how much head work helps these old bikes. I’m pretty stoked.

Any fellow F2, 836cc owners have a cam recommendation? Jetting baseline with the PD carbs? (Using Tintops, "antipod" filter setup? (Yeah pretty unique I know)


Below are some photos of the flashing I am going to clean up. Seems there was a bit of a blob of aluminum in one of the central channels that can’t easily be filed out as seen in the last photo.

[Don R]

 That head looks pretty good compared to a few I have. I think they got better at making them quickly. I've assembled a decent F2 from a junkyard bike and a parts engine I bought for $30. It's just bolted up without gaskets to keep it all in one place. The bike it came out of had under 9 thousand miles on it. The PO couldn't get it running right so rather than figure it out, he swapped it for a known good motor.
 Hopefully I am making enough room in the shop for a blast cabinet.

[grcamna2]

That head looks pretty good compared to a few I have. I think they got better at making them quickly. I've assembled a decent F2 from a junkyard bike and a parts engine I bought for $30. It's just bolted up without gaskets to keep it all in one place. The bike it came out of had under 9 thousand miles on it. The PO couldn't get it running right so rather than figure it out, he swapped it for a known good motor.
 Hopefully I am making enough room in the shop for a blast cabinet.

A good choice Don;blast cabinets 'rock'.

[SOHC4 Cafe Racer Fan]

Are you doing all the head work yourself?  Porting?

I did clean up the casting lines and such in my old head but this time I’m getting things done correctly!

No I am getting this F2 head built by Mike Rieck. Pistons are going to be the 836cc F2 pistons from Dynoman.

Now, we're talking! A MR ported head and high-compression pistons (along with a cam) is a great recipe to level up on performance!

[CB750R]

Was able to pick up some fresh Cam and Primary chain tensioner parts from Honda. Have stripped most the paint off the top half of the lower cases, need to start removing the cylinder studs.

Taking some inspiration from this Japanese build of a custom CB750 for frame reinforcement. I know that this bike will never handle like my track bike or my wife’s VFR400R but with the more modern tires and brakes I have on the bike I might as well attempt to make the frame more rigid.

[70CB750]

Following. 

[CB750R]

Had a bit of a go with the cylinder studs, most came out with heat and double nut, but some put up a lot of resistance. I got a stud removal tool that worked quite well. But still ended up breaking 1 stud several times trying to free it. I tried several times to weld on a nut to the remaining nub but my 110v mig couldn’t get the weld to penetrate into the stud. I took it to a local shop and with a ‘real’ mig they welded a washer then a nut and the stud came out.

I cracked the jaws on the stud removal tool as well, I’d like to pick one of these up with jaws made out of chromoly as they are supposed to be good to use with a 3/8 impact gun.

Good news is they’re all out now and ready for HD studs.

[denward17]

Was able to pick up some fresh Cam and Primary chain tensioner parts from Honda. Have stripped most the paint off the top half of the lower cases, need to start removing the cylinder studs.

Taking some inspiration from this Japanese build of a custom CB750 for frame reinforcement. I know that this bike will never handle like my track bike or my wife’s VFR400R but with the more modern tires and brakes I have on the bike I might as well attempt to make the frame more rigid.

Where did you pick up that cam chain guide? (14611-300-000)
Thanks

[CB750R]

Where did you pick up that cam chain guide? (14611-300-000)
Thanks

I just got it at the dealer.

[denward17]

Where did you pick up that cam chain guide? (14611-300-000)
Thanks

I just got it at the dealer.

Which dealer? I called about 3 this afternoon looking for one...

[CB750R]

Which dealer? I called about 3 this afternoon looking for one...

From Kelowna Honda, Honda Canada had it in stock, it showed up at my local dealer in 2 days.

Cycle-exchange stocks them I believe.

[CB750R]

Little clean up in progress of my stator cover. Still a little more cleaning up to do but I’m pretty happy with the results.

[CB750R]

Little detour as I’m in holding pattern for parts. My wife and I tackled the seat on the Bike a few years back but I never shared it here. I took the old cover off and then shaped the seat foam to have a bit more of a "modern" looking shape profile vs the big black loaf they sort of look like. My wife drafted the pattern for the seat and sewed it up on an industrial machine we found locally for sale. She finished the rear panels with red top stitching to give it a nice little finishing touch. I’ve ridden many hours on the seat with no discomfort and I’m really happy with the looks.

[Jerry Rxman Griffin aka MuthaF'er]

Considering what you found holding the cam caps down, what are the chances the cam is stock?

[CB750R]

Considering what you found holding the cam caps down, what are the chances the cam is stock?

Looks like a stock F2 Cam as I measured lift as .320 and .304 with a dial indicator, my other cam which I believe is a stock k5 measures .300 and .285 in comparison.

At minumum its nice to verify that I have an F2 cam in my stock pile! Would've been nice to find an aftermarket cam sitting here fore me.

[HondaMan]

Question about the cylinders? I see a lot of casting flash closing up holes intended for airflow, does filing these do anything besides make me feel like I’m doing something?

Yep, opening up those holes will let the cylinder(s) cool better, particularly at low speeds.

On the other topic, the 1-2 shift trouble you originally mentioned: that sounds like a bent "L" shift fork.

[CB750R]

Little progress update from the Porting wizard! This is still work in progress and a comparison to my stock F2 head! Man I’m getting excited!

[HondaMan]

Any fellow F2, 836cc owners have a cam recommendation? Jetting baseline with the PD carbs?

Megacycle's 125-00 (or 125-04 in hardweld) is my go-to hi-perf cam for these engines. It is a copy of the Dick Mann cam from the 1970 Daytona win. This one is good on the street, in commuting and touring service as well. It is also made like a Honda OEM cam, extremely durable. I can't say the same for other aftermarket cams I have seen, and many of those had to be removed because they had too much lift (even more than advertised, sometimes) and caused troubles like cracked valve guides, pulled-thru valve keepers, and even burned rocker shafts.

A most-important thing for these F2-3 engines is: get Ken's stellar valve spring retainers. The OEM ones will pull thru and crater the engine for you, as they were merely stamped-steel parts. Ken at CycleX has neatly and succinctly solved the problem with his Valve Spring Retainers for the F2/3 engines, and I use them in every F2/3 engine I rebuild.

[CB750R]

Been trying to keep forward progress. I have finished media blasting the cases and we also just finished some renovations. So used the old dishwasher as a step in cleaning to help ensure that no media gets left in the nooks and crannies.

Also I have a small lathe and mill so I’m taking a crack at making some frame adapters. My mill is having a hard go on steel so it’s a very slow process.

Also spent a weekend doing a valve clearance and tune up on my dads "new" track bike. We picked this thing up for scrap value after owner suspected he blew a head gasket. I gambled that it was the common failure of the oil cooler and seem to be right. Ive flushed the heck out of oil and cooling system and checked compression inspected the cam towers for damage etc. this is going to be a great bike for my 66 yr old dad to continue doing track days with me.

[CB750R]

Welded in the cycleX frame clamps over the weekend. Weather is wet and cold all the running bikes are put away so it’s time to get back into project season!

[Stev-o]

It's been a year, what is the status?

[CB750R]

It's been a year, what is the status?

It runs great, I have ridden it several times however I kept seeing aluminum in the oil I've changed the oil after almost every ride probably done 8 oil changes on it so far, and unfortunately was pretty disheartened and let it sit in the shop. the material in the oil is non ferrous.

However I took the valve cover off again looking for my "smoking gun" found nothing, took my clutch apart and I think I found it...

I bought a Cycle-X reconditioned oil pump to rule out any possibility that my oil pump was eating itself, however upon inspection it looks fine.

I used an APE "extra clutch disc" setup, but got lost between the early small baskets and the thicker 77/78's and I think I over filled the clutch with too many plates. I think when the clutch lever was pulled in, I was pushing the inner hub into the basket? there's evidence of scoring on the back of the inner hub..

I've replaced the clutch with OE parts, aside from clutch springs, I primed the oil system tonight and its about 15C in my shop but got 78psi cold which is good, I'm getting 180psi cylinder pressure cold. so I'm hoping I have solved my "teething" issues and haven't caused damage to the engine otherwise.

It runs so so well I'm beyond happy with how well it all came together, just makes me a bit sick trying to figure out where this metal was coming from in the oil.

[HondaMan]

Yep, that backside of the pressure plate does look a little close!