Author Topic: 1975 CB750F Project - Total Rebuild (Read 21822 times)

Kickstart · « **on:** May 30, 2012, 09:26:02 pm »

I finally got around to starting the rebuild on my 75 cb750f project bike. I had meant to start it over the winter, but better late than never.

Sorry about not having a before picture, it wasn't until after I stripped down the frame and took the engine out that I remembered I wanted to document and post my progress here. The bike actually ran before, but it was just in rough shape.

My goal is to rebuild this bike as a strong highway cruiser... max out the performance (as best as I can afford) while not sacrificing the reliability or user-friendliness of the original stock design. I'm planning on keeping the stock look as much as possible, with just a few custom cosmetic tweaks to give it a little individuality.

Current plans for the engine:

Bore out cylinders +1 (pistons from Z1Enterprises) - just to get them back to round bores (as suggested in HondaMan's book)
Install new APE valve guides
Install an adjustable APE cam sprokect so I can advance the timing 8 degrees (as suggested by HondaMan)
Probably a bunch more little stuff - depending on what I find during the tear down

Oh... and I've already sent my swing arm to Hondaman for new bushings, and plan to install a HM transistorized ignition.

Attached are some pictures of where I'm at now:

Stripped down frame - everything removed - planning on having it powder coated and possibly getting the seat re-foamed by Pirate upholstery . Currently the frame and seat are doubling as a book stand for HondaMan's book as I tackle the engine tear-down.

Big box of parts from the bike. Tank, side covers, and tail piece are with a friend for painting. I'm sure this box of parts sitting in the middle of my small garage won't get in the way.

engine with valve cover removed

Close-up of the 3 and 4 intake rockers and rocker shaft - I'll have to measure the wear on the shaft. (engine has 20K on it)

Rocker towers off - I'm having a lot of trouble getting the head off. Last time I did this the engine had a head gasket leak and the head came right off... this time it's a different story... I'm taking my time as I don't want to damage any fins.

harisuluv · « **Reply #1 on:** June 02, 2012, 09:50:29 pm »

Good luck with your project. Are you going to go for a more stock look?

Kickstart · « **Reply #2 on:** June 06, 2012, 09:03:50 pm »

Thanks Harisuluv

Yes, I'm going for more stock than not (at least that's what I think I'm doing).

I really like the look of the the F0 model, especially the stock 4-1 exhaust and muffler. However, I'm not doing a restoration.

I'm thinking about the following changes cosmetic-wise:

- Paint the tank and rear cowl black (they're currently this color but need to be re-done)

- Put on the '75 cb400f bars

- Install bar-end mirrors

- Install adjure diamond cut headlight

- Maybe make custom face-plates for the speedo and tac

- Maybe install some accessory gauges - oil pressure, voltage, clock? - but only if I can do it with older style gauges (I want to keep a vintage look, if that makes sense)

- I not sure what I'm going to do with the seat. I would like to add some subtle character here, but with a vintage look. I saw Dagersh's thread where he had Pirate Upholstery make a brown leather seat http://forums.sohc4.net/index.php?topic=35057.msg1120581#msg1120581. I wanted to do something similar, but it turns out leather isn't really practical for a touring bike (unless I'm very diligent about putting a seat cover on every time it rains), and I wanted a mix of mostly black and some brown (which I'm not sure is even possible), oh... and it's extremely expensive.

Otherwise, I just want to build a clean, great performing, highly reliable, long lasting bike I can ride hard and take on long trips.

harisuluv · « **Reply #3 on:** June 07, 2012, 02:18:21 pm »

I'm with you, I'd love for it to look pretty but first and foremost I want it to be reliable and be able to perform.

Kickstart · « **Reply #4 on:** June 07, 2012, 05:02:21 pm »

I just clicked on you build thread... nice work on restoring carbs!

I was also thinking about soda blasting my carb bodies, but I was wondering what's on the bowls. It seems like the bowls have a clear coat on them... is this true? If so, will soda blasting take off the clear coat or will I have to sand that off? And, as a follow-up, can they be re-painted or is it better to just leave them bare?

Thanks,
Chris

Kickstart · « **Reply #5 on:** June 22, 2012, 04:58:17 pm »

I made some more progress today.

Got the head off (I had a lot of trouble until I noticed I forgot to remove the four nuts that are right next to each spark plug)

Getting everything ready to take to the machine shop. Unfortunately, I noticed I managed to ding up my head. I think I did this when fishing the cam chain through the head. I must have inadvertently rested the head on the cylinder studs (or somehow bumped them without noticing).

Yikes!

hmm... will this leak now...

Not sure if this is repairable or not.

Kickstart · « **Reply #6 on:** June 22, 2012, 05:09:24 pm »

Here are some more pictures:

Scored piston... not worried about this since I'm boring it out with new pistons. #4 (this one) had the most scoring).

Some rust on the #4 side as well. I'm not sure if I should be worried about this. Odd that this stud had a bunch of rust (all the others were fine.) There's also some surface rust on the rod. Makes me wonder if I have more rust lurking in the engine.

Dissembled head. I'm sure this cluttered workbench won't be a problem

Kickstart · « **Reply #7 on:** June 30, 2012, 07:47:30 pm »

Slowly making progress...

I got the shift cove and alternator off:

I'm worried about all the surface rust I'm seeing. There's some on the flywheel above, and all of my rods have surface rust on them (picture below). Is this an issue? Do I need to clean this up or is this harmless?

Kickstart · « **Reply #8 on:** June 30, 2012, 07:52:53 pm »

Also, speaking of rust.

The front outside stud on cylinder 4 has a bunch of rust in the recessed area of the case. I believe this is where one of the alignment dowels goes. Can I just clean it out with wrench oil and some toothpicks (or something), or should I be replacing this stud?

harisuluv · « **Reply #9 on:** July 03, 2012, 11:07:51 pm »

Thanks!

Yes those bowls and caps are coated with that Honda factory clear coat. Soda blasting will definitely take it off, although there are variables. If they have been exposed to some weathering or been outdoors it will kind of harden and deteriorate the clear coat and it will come off quickly and visibly. Sometimes the clear coat can be a little more stubborn. Sometimes if someone in the past has gotten into them and they have added some custom gasket sealer I will give them a dip in carb dip to eat that stuff up. It will also take off that clear coat if there is any remaining or soften it up for blasting.

It isn't really essential for me to get every bit of it off as I polish them anyways and if needed use some greaseless abrasives.

I have looked into "finishing" after polish but even everything on the market is meant to protect for around 3 months and then you have to redo it. In my opinion, a polish or just the blasting is good, it is aluminum so it is not going to rust like steel. It will oxidize slowly but won't rust.

Quote from: Kickstart on June 07, 2012, 05:02:21 pm

I just clicked on you build thread... nice work on restoring carbs!

I was also thinking about soda blasting my carb bodies, but I was wondering what's on the bowls. It seems like the bowls have a clear coat on them... is this true? If so, will soda blasting take off the clear coat or will I have to sand that off? And, as a follow-up, can they be re-painted or is it better to just leave them bare?

Thanks,
Chris

SOHC4 Cafe Racer Fan · « **Reply #10 on:** July 04, 2012, 06:21:04 pm »

Harisuluv's work is amazing. I just did a carb swap with him and you can eat off the rebuilt carbs he sent me. He's got a fast turn around time, fair pricing and top notch workmanship.

Mcwilliams570 · « **Reply #11 on:** July 05, 2012, 07:56:08 am »

Looking good so far man. Almost done with mine hope to hook up soon and go for a ride with you..

Matt

Kickstart · « **Reply #12 on:** July 06, 2012, 08:16:55 pm »

Thanks Matt!

I read through your build thread... very nice work on the 550.

Kickstart · « **Reply #13 on:** July 06, 2012, 08:34:02 pm »

Split the case last night.

Most everything looks OK - except for one bearing on the crank (I think it's the third one in). It looks like there was a void in the casting? Anyone know if this is something I should be worried about?

Pictures attached.

I haven't decide if I'm going to send the case off to be professionally painted, or try to do it myself. I want this build to last a long time, and I'm not sure if the VHT/Duplicolor spray paints have the longevity I'm looking for.

jstub9 · « **Reply #14 on:** July 14, 2012, 06:15:34 am »

Good work. I'm planning on stripping my 75 750f in similar fashion this winter.

Kickstart · « **Reply #15 on:** July 23, 2012, 10:11:11 pm »

wow... it's been over two weeks...

I used plastigage on all my journals...

Rod journals (on the crank) are all around 0.002"
Crank journals are all around 0.0015"

I had a scare about some pitting on the journals.... but it sounds like I can just polish the surfaces and I should be good:
http://forums.sohc4.net/index.php?topic=109588.0

I think I'll look into replacing the bearings to tighten everything up.

Some pictures attached.

Kickstart · « **Reply #16 on:** July 23, 2012, 10:13:27 pm »

Some more pictures... including the oil pump screen (not too bad... just saw a few small metal shavings).

Oh... does anyone know what those numbers on the crank mean? (I thought journal sizes were either 3,4,5 or letters)

J.Webster Designs · « **Reply #17 on:** July 24, 2012, 07:40:24 am »

I am not sure about some of your other questions, but I would like to tell you about my experience with the VHT engine paints....

I would personally have the cases sent off for paint or powder. The VHT does a good job for what it is. How ever, just like any other spray paint, it will scratch easily and is extremely prone to damage from everything else including chemicals.

if you are up for it, take the time to get it done with a nice paint, or powder.

Jerry Rxman Griffin aka MuthaF'er · « **Reply #18 on:** July 24, 2012, 08:40:29 am »

Those are NOT Honda numbers. Your crank was probably lightened and balanced?

Kickstart · « **Reply #19 on:** July 25, 2012, 08:38:07 pm »

Thanks for the advice Midnight08.

I was thinking about having the powder coating place I'm using for my frame do it, but they only have sand/glass bead blasting and I'm not sure I like the idea of getting sand in my engine case. I question how well I would be able to clean everything out.

Kickstart · « **Reply #20 on:** July 25, 2012, 08:42:13 pm »

Quote from: Jerry Rxman Griffin on July 24, 2012, 08:40:29 am

Those are NOT Honda numbers. Your crank was probably lightened and balanced?

I don't see any other evidence that the crank was touched (or that the engine was split before) - at least not that I can tell. Odd.

I was able to find the real markings of the journal sizes elsewhere on the crank.

Kickstart · « **Reply #21 on:** July 26, 2012, 11:09:33 pm »

Here's a picture of the journal numbers on my crank.

Hard to tell in the picture, but it's AAAAA for the crank journals and 4444 for the rod journals.
My case has BBBBB stamped in it, and all my rods are #2.
This should mean all my bearings are green ones (both the crank and rod bearings)... at least that's what it says in the shop manual.

I'm not sure yet if I'm going to replace the bearings. I don't think I have to, but since I've got everything apart I'm thinking I might get my crank journals polished and replace the bearings. Of course that's another $300 to the project costs.

aperry · « **Reply #22 on:** July 27, 2012, 01:35:52 pm »

Regarding paint, I would have it done professionally, especially with all the work you're putting into the engine.

I went with Duplicolor "High Heat Engine Enamel" and found that it chips very easily. I scratched it up pretty well installing the engine and then chipped it in various places with everything from dangling spark plugs to dropped screws. It's terrible with gas. I had to spend some time resolving carb and petcock leaks, which took off a considerably amount of the paint in certain areas. It's possible I didn't clean the engine well enough, and I also used a soda blaster which I've since learned to have negative effects on adhesion. So YMMV.

If you can find a high-heat rattle can 2K clear coat to seal everything in, that would be best. I used Spraymax on my tank and seat and it's good stuff, however I had trouble finding it's temperature limits in the data sheet. It isn't advertised for high heat applications, so I'm assuming it won't stand up to engine heat.

If you have a spray gun then I'd also take a look at POR high temp paint. I like their other paints. Pretty tough stuff.

Aaron

Jerry Rxman Griffin aka MuthaF'er · « **Reply #23 on:** July 27, 2012, 01:52:40 pm »

Even if you have the crank work done you may still be able to reuse good bearings once you Plastigage it

Kickstart · « **Reply #24 on:** July 27, 2012, 08:51:56 pm »

Quote from: aperry on July 27, 2012, 01:35:52 pm

Regarding paint, I would have it done professionally, especially with all the work you're putting into the engine...

and I also used a soda blaster which I've since learned to have negative effects on adhesion...

Yeah, I read through a bunch of painting threads here... sounds like the VHT/Duplicolor route is real hit-or-miss, and probably not worth taking the chance since I want to do this once and not have to touch it again for 10+ years.

I found a local guy who does motorcycle painting, and sounds like he knows what he's doing. Rough quote was $300-400 to do the engine... but that was just over the phone. He doesn't blast the parts (just cleans and sands them real well, so I'll have to do that myself if I want to get it that clean).

You bring up a good question on soda blasting... does it really create an adhesion issue? (I guess some of the soda gets embedded in the aluminum?)... I wonder if that can be cleaned/baked out? I really didn't want to sand/bead blast the cases and then have to worry out a rouge piece of grit hiding out in one of the oil passages.

Maybe I'll just spend a few long weekends with some scotch pads, sandpaper, and rotory tools... and just be OC about sanding every little nook and cranny.

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Author Topic: 1975 CB750F Project - Total Rebuild (Read 21822 times)