Topic: 1978 CB750F3 rebuild start

[majorzozo]

Just started rebuilding a rusted out 1978 CB750F.  Thanks to all at this forum as i have used so much of the information provided.  Just finished the engine.  Standard 61MM pistons, new rings, honed.  All new seals O'rings and gaskets.  10 between the case and cylinder which was 4 around the steel sleeves, 4 on the un used cylinder studs, and 2 between the inboard cylinders.  6 used between the head and cylinder along with 4 metal spacers which were wrapped with large wide O'Rings and 2 between the inboard cylinders.  On top of the head used 6 hockey pucks, 4 brass washers under the cap nuts and 4 O'Rings.  Used Permatex Aviation sealer nder the cylinder.  Head gasket was dry. Paint used was Dupli-Color Semi Gloss Black DE1635.  First time rebuilding so hopefully no leaks.  Next is the reconditioning of the Comstars.  They are so bad will probably paint.  Again, thanks to all.

[denward17]

That looks really good major.

What is after the wheels?

[majorzozo]

Thanks Denward.  The forks.  Totally rusted out but they are oddballs.  35mm by 23 inches.  Cannot find anywhere.  I'll keep looking.

[denward17]

Understand, keep your eyes peeled in the For Sale sub-forum, never know, they might pop up..

[seanbarney41]

For sure...I just  bough some here.  Guy might have some more...
forums.sohc4.net/index.php/topic,191638.0.html

[majorzozo]

Awesome, thanks guys I will....

[scunny]

is that some sort of hyper link ?

[seanbarney41]

Scunny, I don't rightly know.  I used to be able to just drag and drop from my browser and it would show up as a clickable link.  For some reason, that does not work anymore.  If anyone knows what I am doing wrong, let me know.

[RAFster122s]

Forking by Frank can supply all kinds of fork tubes and custom lengths if required. They normally have stock Honda CB sizes on hand…

[PeWe]

is that some sort of hyper link ?

Link work fine if copy and paste into a browser.
I copied link in my browser and paste it here direct when writing.
http://forums.sohc4.net/index.php/topic,191638.0.html

[BenelliSEI]

Very nice work. Looks outstanding.

[70CB750]

What did you do about the head?   F3s are known for eating valve guides. 

[majorzozo]

Bike only had 13,000 miles on it or so they said.  The valve guides were tight so I just cleaned, lapped, and replaced the seals.  Ran good before disassembly.  Another weird thing was the pistons.  They had raised metal numbers on the sides where the recessed unpolished areas were.  I had two number 1's and a 4 and a 3.  No number 2.  It appeared the engine was never taken apart but find it weird it would come from the factory that way.  They also were not in the correct order when disassembled.   

[70CB750]

Bike only had 13,000 miles on it or so they said.  The valve guides were tight so I just cleaned, lapped, and replaced the seals.  Ran good before disassembly.  Another weird thing was the pistons.  They had raised metal numbers on the sides where the recessed unpolished areas were.  I had two number 1's and a 4 and a 3.  No number 2.  It appeared the engine was never taken apart but find it weird it would come from the factory that way.  They also were not in the correct order when disassembled.

Too much saké that day 

[denward17]

Bike only had 13,000 miles on it or so they said.  The valve guides were tight so I just cleaned, lapped, and replaced the seals.  Ran good before disassembly.  Another weird thing was the pistons.  They had raised metal numbers on the sides where the recessed unpolished areas were.  I had two number 1's and a 4 and a 3.  No number 2.  It appeared the engine was never taken apart but find it weird it would come from the factory that way.  They also were not in the correct order when disassembled.

I don't think those numbers represented sequence, but I am not sure.  My K8 had 3 7s and 1 6, I think....The important number for me is 392.

[majorzozo]

Thanks Denward.   Must not mean anything.  Makes me feel better with the only other suspicious thing being the fork tube length of 23 inches.  Most everything I look up shows 23 7/8.  Thanks again...     

[newday777]

Bike only had 13,000 miles on it or so they said.  The valve guides were tight so I just cleaned, lapped, and replaced the seals.  Ran good before disassembly.  Another weird thing was the pistons.  They had raised metal numbers on the sides where the recessed unpolished areas were.  I had two number 1's and a 4 and a 3.  No number 2.  It appeared the engine was never taken apart but find it weird it would come from the factory that way.  They also were not in the correct order when disassembled.

Welcome aboard the forum majorzozo

Here's a good read on the guides, (I just did a search),
 especially post #5 but read all through the thread.

http://forums.sohc4.net/index.php?topic=10540.0

[majorzozo]

Thanks the valves were tight in the guides.  No lateral play.  Very good read.  Would anyone have any idea why my fork tubes are 23 inches?  Everything i read says they should be 23 7/8.  I am concerned if i was to purchase new tubes that are 23 7/8 my springs would be too short.  Does anyone have any experience with this?  Thanks in advance all.

[RAFster122s]

Sections of schedule 40 pvc plumbing pipe that fit inside the tube can be used as spacers to preload the springs. Commonly done for tuning on the cheap...

[newday777]

Thanks the valves were tight in the guides.  No lateral play.  Very good read.  Would anyone have any idea why my fork tubes are 23 inches?  Everything i read says they should be 23 7/8.  I am concerned if i was to purchase new tubes that are 23 7/8 my springs would be too short.  Does anyone have any experience with this?  Thanks in advance all.

I don't have an F3 so I'm not sure what length the fork tubes are supposed to be. Did you look up the spring length service limit in the service manual to measure your spring length? You would be best off buying Race Tech springs for your weight and their Gold Valves to add damping adjustment for better handling. I've bought new Race Tech springs and Gold Valves for my Goldwing and the handling was vastly improved. They include a length of aluminum tube to make spacers you cut to length to give the proper preload on the springs (Raf mentioned you can use schedule 40 pvc pipe to make preload spacers too)
Maybe someone put in shorter fork tubes to lower your bike??
Call Frank's Forks to see what they have to say about it. (M-F) They've been doing fork tubes for a long time.
They make and sell new fork tubes to length.

[newday777]

https://franksforks.com/

[majorzozo]

Rafster and newday thank you both.  This site is great. 

[RAFster122s]

Note when using PVC pipe as preload spacers use a large fender wash above and below it to provide wear protection for the plastic pipe...
Cheap and easy tuning aid for the front suspension.
 
The Race Tech Gold Valves are fantastic solution for our early forks to save you a ton of money retrofitting a more modern adjustable/tuneable fork design onto the bike.
Lots of guys who race in AHRMA and the Canadian equivalent that escapes me at the moment will use the Race Tech Gold Emulator valves in their race bikes.

They may seem pricey, but they really aren't considering the expense of grafting a more modern fork onto the bike...
 
David

[majorzozo]

Thanks again.  Just finished painting the wheels.  Used Seymor Alumi-Blast.  Sand blasted then used 320 and 600 grit sand paper, primed and painted.  Obviously would have been better not to paint and clean but they were in bad shape.  Next time I think the route to go would have been to try Aqua blasting.  For how bad they were they came out OK for me.  Next will be positioning the engine sideways and dropping the frame over the engine.     

[BenelliSEI]

I just pulled all the engine covers off my project. They look about the same as your wheel (before). I’m going to try vapour blasting and see how that works, before my usual: clean, scrub, polish sequence. Wheels look great!