Topic: CB 750 Project 1 - Rides Well but a few tweaks needed

[timbo750]

Hi All
Thought I might share the project I am starting, it will actually be the first of 2 (maybe more later) as I set out to find a project bike and ended up with what I call almost 2 bikes. The odd thing is I could not make 1 complete bike between all the parts I had but i still thought i was on a winner.
This project will be the first (obviously) and will accommodate two up as the wife and 2 boys want to come for a ride at some point. The other will be Mine all MINE!!!!!!
I hope to share the highs and lows of the journey I take and hopefully someone will learn from my mistakes or at least be able to laugh at them.
This project was the almost complete bike I got which I was told the engine was seized, but not being bothered by a challenge i wasn't fussed. Well seized was an under statement, it had been drowned and the photo's speak a thousand words (some of them we wont mention).
the motor is almost completely apart and i have started cleaning.
Wish me luck, or at least to maintain sanity.

[70CB750]

Scary pictures!  Good Luck!

[tool14]

good luck with your project.

[fire113]

...clutch basket is looking like water cooled

Good Luck

[timbo750]

Well I have had some success with cleaning the rust of the engine parts. I soaked everything in vinegar for about a week, anything that was left on the parts would come of with a soft brush. Unfortunately some of the gears are pitted - not deeply, but enough that they will wear quickly if I use them, but some of the parts came up quite well considering how they bad they looked.
Also I have a broken cooling fin on the cylinder block, can anyone tell me if this will effect the engine whilst running, I know it wont look right but I just want this bike to work?

[Vinhead1957]

Really won't effect cooling much but it would be ugly. A shop could weld a new fin on pretty easily.

[Vincent P]

All I can say is DAM!!! and Good Luck. Will follow this thread for progress.

[timbo750]

I have been going through the process of removing all the bearings from the gear box and as you can imagine from the water that was in the engine they all need replacing. The bearings giving me the most grief are the two small needle roller bearings inside the primary drive sprocket.
In an attempt to remove them they have disintegrated on me and not moved at all, does anyone have any hints or ideas to ease my frustration. Also in my attempts to search for an answer I found out about the replacements of the rubbers but I am not sure how to check if they need replacing, the gears are good and there is no rattle.

[754]

Just get a used one, would be cheap over here.
 Bet that fin broke, because the small bolts were still in the head. If you fix the fin by welding completely, you will probably have to resurface the head.
 Some things easier just to buy parts motor
  The pitting on the gears ..think of it as oil retention..really old bike like 30s  or older get lots of that
 Be a lot of satisfaction getting that running..

[HondaMan]

I have been going through the process of removing all the bearings from the gear box and as you can imagine from the water that was in the engine they all need replacing. The bearings giving me the most grief are the two small needle roller bearings inside the primary drive sprocket.
In an attempt to remove them they have disintegrated on me and not moved at all, does anyone have any hints or ideas to ease my frustration. Also in my attempts to search for an answer I found out about the replacements of the rubbers but I am not sure how to check if they need replacing, the gears are good and there is no rattle.

At this point, I would strongly suggest getting a used gearset with clutch. The bearings inside the gears are cast iron on the bikes made after 1973, so will also be in bad shape from that much water. The needle bearings in the primary drive are hard to come by (no sizes available from Honda).

So, to find a good tranny: what model/year is it? The year and month should be on the steering neck, and the engine's serial number will get us all close enough to help find a tranny. There are 4 distinct trannies in these bikes. The early 2 swap with each other, the later 2 with each other, but the early and late are a Rubik's Cube if you try to piece them together.

Look CLOSELY at the shift drum, especially in it's grooves for the shift fork's pins, and the shaft the forks slide on. These must be pristine, or you will not be able to shift when the engine is hot.

[Lazerviking]

Wowzers, looks like you have your work cut out for you. I'm excited to see how this project comes along. Good luck!

[timbo750]

Guys, thanks for the advice. I have ordered a whole gear set complete with shift drum and forks from eBay but I did not know about the 4 types that HM mentioned hope I got the right one as it has already been sent. I had heard about the different gear ratios before that's all.
Anyway about the only thing its missing that I will need is the primary drive gear, the clutch basket is ok, I will just need new clutch plates no big deal there.
I have been told the fin is not a big deal to get welded but I also have one of the lower front mounts that is broken and will need welding as well and will get both done before any machine work gets done.
HM is there any way to tell the difference between the 4 gears sets? I am certain the engine is not the original for the frame.

[acollin]

When you take on a project such as this, do you create a budget?
 Would you state what to expect when all is done?
Money in and value out beyond the fun of doing the project?
Thanks and good luck

[edwardmorris]

Subscribed.

[timbo750]

For anyone that may be able to enlighten me on manufacturing dates of my bike,
Engine Number : CB750-2342574 - K4?
Frame Number : CB750-2085442 - K2?
Also under the black paint of the frame there is a Bronze/Gold colour paint which I am assuming is from a previous owner doing some changes, most likely when the engine was swapped.

[edwardmorris]

For anyone that may be able to enlighten me on manufacturing dates of my bike,
Engine Number : CB750-2342574 - K4?
Frame Number : CB750-2085442 - K2?
Also under the black paint of the frame there is a Bronze/Gold colour paint which I am assuming is from a previous owner doing some changes, most likely when the engine was swapped.

Try http://www.sohc4.net/cb750k-serial-numbers/

[lucky]

Those parts that were rusted need to be bead blasted.
Especially that clutch basket and that steel gear.

Also vinegar with water makes steel rust even faster.
Spray all of those parts with WD40. OR put engine oil on them.

[timbo750]

Those parts that were rusted need to be bead blasted.
Especially that clutch basket and that steel gear.

Also vinegar with water makes steel rust even faster.
Spray all of those parts with WD40. OR put engine oil on them.

Lucky, can you tell me what the Bead blasting will actually achieve? I am asking this because the parts that actually am going to reuse, I have managed to successfully remove all the rust (probably 99% in reality), I am asking this because I am still learning some of these things.
I found out about the flash rusting too, and had to do some items again. the process of stopping that ends up being several steps and I actually think that the vinegar ate into my shift drum because it only had some minor rust and now its a paperweight.
Next time I will look at the electrolysis method especially for critical parts.
I will post photos of the cleaned parts before and after.

[cakey]

Good work Timbo.

I sent off my barrels to get welded at a place here in Darwin this week and should have them back by tomorrow. They seemed to think it wouldn't be a problem but I will get it checked when the barrels get bored out next week.

I have been sourcing a lot of my parts for my ground up rebuild from David Silvers, CSMNL and a guy in WA who deals in new and second hand parts for the CB750 and is great to deal with as well. I just put his transmission bearing kit through my K1 engine.

Good Luck mate.

[timbo750]

Good work Timbo.

I sent off my barrels to get welded at a place here in Darwin this week and should have them back by tomorrow. They seemed to think it wouldn't be a problem but I will get it checked when the barrels get bored out next week.

I have been sourcing a lot of my parts for my ground up rebuild from David Silvers, CSMNL and a guy in WA who deals in new and second hand parts for the CB750 and is great to deal with as well. I just put his transmission bearing kit through my K1 engine.

Good Luck mate.

Thanks, I had not heard of David Silvers they have a lo of stuff put the pricing in pounds always gets me. I have had a look at CSMNL before but they seem to be priced on the high side. Is the guy in WA the same guy I see advertised on gumtree? I will need to replace all the bearings as well but I am having trouble with the needle roller bearings in the primary drive sprocket, looks like I might have to spend nearly $200 on tool I may only use once. Did you replace these bearings and if so how?

[cakey]

Sent you a PM mate.

[timbo750]

thought I would post a photo of some cleaned parts, I am pretty happy with how they have finished when you compare to photos above. I am hoping to get parts over for machining this week too, turns out he can weld the fins and crank case for me as well. Gotta love a one stop shop.

[timbo750]

Went and dropped into my mates workshop this afternoon, to get him to look at the engine. Was worth the 3 hours talking shop and getting hands the hands dirty.
The crank is all good, its 1 thou out from straight and the journals are all good. The head far better than expected once the valves were removed and you could see it all, I will be getting valves -slightly bigger and slightly different. I knew this guy was good but he is a wiz and loves his work and loves a challenge.
The valves will be from a car along with the springs, retainers and collets. The springs where left over from and engine that had been modified, we checked on the gauge and they have the same pressure through compression range, the retainers need slight machining but an easy fix, and he can make new valve guides to suit.

While I was there got the engine mount welded, all it needs now is some machining and it will be like new. He will also show me how to port the head so I can take it away and do that myself before it gets reassembled.
All I have to do is get the pistons and rings, and also finish the rest of the bike.

Also I am wanting to get the book written by Hondaman, I am gathering by his wealth of knowledge that I have on this forum that it is worth every cent and then some for all the little tricks that no other manual has.

[timbo750]

Just an update, not much seems to have progressed but there are always stages when you spend more time finding solutions and researching than actually fitting or replacing parts.

Got the tank filled up with vinegar this afternoon, so next week should be able to drain and neutralize. By the way, I read somewhere that the fuel tank was 19 litres - Crap, its 17 litres full to the brim.

Had some issues with the carbs and ended up resorting to the spare set I was keeping for the next bike, seal kit is ordered but still have lots of cleaning to do in those hard to reach spots.

started on the head on Saturday, all the engine is at my mates workshop at the moment so it will only move when I can get there but will be doing the porting next time I am there and I am hoping to convince him to put it on the flow bench to see what we get.

Tried to source the gearbox bearings today and got fed what I thought was Bull$hit. The guy said that Honda usually used different versions of bearing's and that if he sold me the common variety (as per the number) then he might be liable if they fail, so he is on my list of never deal with again and I will try some elsewhere tomorrow.

[timbo750]

Haven't had much to report on as a few things are half done. The engine is at the machinist (who is a mate) but he isn't doing anything unless I am there - he doesn't normally do bikes but he is saving me a lot of money. I have ordered most of the parts I needed for the rebuild from Dynoman, excellent service an quick turn around.

got all new gear box bearings I got off the shelf bearings with no trouble they all cost me $125 including 2x primary gear bearings. I went with the units with the smaller groove than the standard Honda and decided to very delicately grind the original snap rings to fit the narrow grove and they fit the groove in housing. it only took 5 mins to grind each one with a Dremel.

getting some stuff ready to get re-chromed and need to my seat the local upholstery guy and see what he can do, I have a seat from a 77 cop bike which I am pretty sure is original quite a different shape padding than the standard bike and good option for two up seating.

I have been trying to find someone local here in OZ for an exhaust but not having much luck, it has 4-2 but has no mufflers and needs re-chroming. might to buy mufflers from the states and fix it myself.