Honda-SOHC

SOHC.co.uk Forums => CB750 => Topic started by: Shetland Biker on April 05, 2024, 05:10:36 PM

Title: Opening that can of worms
Post by: Shetland Biker on April 05, 2024, 05:10:36 PM

Hi there,  posted a while ago when i joined the forum,  unfortunately life got in the way for a little bit,  but i have finally got my 1978 cb750 project bike.  one thing im thinking is to send the engine away to get properly looked at, change piston rings, seals, gaskets, and just have someone look at it.  i have no history on the bike. so im thinking i dont know who has had it open or done what to it.  so if im going to restore this bike i may as well do it properly from the start.  i do have some mechanical knowledge but not enough to strip and rebuild an engine even with todays youtube guide.  so after that long winded intro. my question is,  is there a go to place to send a cb750 SOHC engine to get looked at?  also if anyone has a rough price on what said work might cost providing they find nothing majorly wrong with the engine? thanks in advance.  and be sure this will be the first of very many questions lol.

Title: Re: Opening that can of worms
Post by: Bryanj on April 05, 2024, 05:18:45 PM

Your first problem is finding somebody to work on it, second is what model is it? Just saying 78 means nothing.
Parts alone can be anything from a couple of hundred to several thousand depending on what is found inside, there is no such thing as an "average" rebuild, every last one you lay spanners on needs different things.
You need a gasket set and oil seal set just to take it apart and put together, then depending on model, valve guides, cam chain+tensioners, primary chains+ tensioners, pistons etc etc.
Where are you?

Title: Re: Opening that can of worms
Post by: SteveD CB500K0 on April 05, 2024, 05:27:28 PM

A long way from you Bryan


Sent from my iPhone using Tapatalk

Title: Re: Opening that can of worms
Post by: Bryanj on April 05, 2024, 05:28:55 PM

A long way from anybody if it is Shetland Steve! So that would add a few hundred for 2 way carriage

Title: Re: Opening that can of worms
Post by: Shetland Biker on April 05, 2024, 05:47:13 PM

yea im up in Shetland, which is a huge pain in the ass sometimes.  how would i tell what model? would that be from the start of the frame number?

Title: Re: Opening that can of worms
Post by: Nurse Julie on April 05, 2024, 05:50:24 PM

Show us a picture

Title: Re: Opening that can of worms
Post by: Shetland Biker on April 05, 2024, 05:58:12 PM

hopefully this works

Title: Re: Opening that can of worms
Post by: Orcade-Ian on April 05, 2024, 06:02:00 PM

It is a can of worms but you have many skilled folk who are into bikes in Shetland.  Have you contacted anyone involved with the Shetland Club?  People like Colin Nicholson, Geordie Jacobsen, and Joe Gray might point you in the right direction and although they might not be pure Honda folk, I'm sure they will know people who are.
Speaking personally I wouldn't send a completely unknown unit to an equally unknown 'expert'.  Surely there are people who could guide you through the dismantling process and individual components can then be assessed for wear and possible replacement.  Following that then this Forum will be able to make sensible suggestions.  We also have quite a few 750 SOHC folk down here in Orkney who I know would offer advice and encouragement.  You would also learn a lot more about your bike and be in a better place to keep it running in the future.

Ian

Title: Re: Opening that can of worms
Post by: Nurse Julie on April 05, 2024, 06:07:13 PM

CB750/4 F1 with F2 wheels, or a F2 with the barrels painted silver instead of black 🤔🤔🤔

Title: Re: Opening that can of worms
Post by: K2-K6 on April 05, 2024, 06:12:48 PM

Looks full F2 rolling chassis etc, but motor appears previous to the F2  original.

Seems to have something like a Suzuki GS 750 type instrument binnacle though.

Title: Re: Opening that can of worms
Post by: Shetland Biker on April 05, 2024, 06:22:38 PM

yea the clocks arent honda.. thanks Orcade Ian for the pointers,  not sure i know the people you names,  but would be happy if you could put me in contact with them

Title: Re: Opening that can of worms
Post by: Bryanj on April 05, 2024, 06:28:34 PM

I would guess, and i stress it is a guess, that is an F2 that has been fitted with either an earlier top end OR been apart and media blasted to remove black paint.
There is no way of knowing till its in bits.
If you want to post the frame and engine numbers it would help with identification. Also extra pics of clocks and rear end might help as well

Title: Re: Opening that can of worms
Post by: Shetland Biker on April 05, 2024, 06:36:22 PM

i can say the clocks arent honda at all,  they have been put at somepoint,  i will get more pics when im next over at the garage.  i was told it was a f2, but thats not to say is the same engine.

Title: Re: Opening that can of worms
Post by: Orcade-Ian on April 05, 2024, 06:44:16 PM

Hello again,
I think Colin Nicholson is still Chairman, so I'll PM you with his email address, I'm sure he can point you in the right direction for help.  I'm not a 750 buff but as you can see, there are lots who are!  Apologise to Colin for 'dropping him in it.  I'm away in Germany and Austria so will miss the big show at the Clickimin in June.

Ian

Title: Re: Opening that can of worms
Post by: Bryanj on April 05, 2024, 06:45:23 PM

Untill its apart you cant be certain what has been done, i would happily rebuild it but i will not get invlved with any sort of media blasting or repainting as i have neither facilities nor inclination to do that

Title: Re: Opening that can of worms
Post by: Shetland Biker on April 05, 2024, 07:01:36 PM

dropped you a message BrianJ.  cheers for that Ian i will get in contact with him

Title: Re: Opening that can of worms
Post by: DomP on April 05, 2024, 08:18:44 PM

Get stuck in!  Rebuilding your own engine is very rewarding if you've got a good range of tools, I've not long finished mine with some helpful advice on here and a rebore from Bryan.  Oh and as Trigger suggested to me in the beginning £1K +

Title: Re: Opening that can of worms
Post by: McCabe-Thiele (Ted) on April 05, 2024, 09:04:40 PM

I don't know your age or mechanical demographic but I'm with DomP on this one.
My only reservation is the 750 engine is pretty heavy so you will probably need a hand to lift it out.

I was 72 when I fully dismantled my 400 having done nothing on a motor cycle engine since I was a teenager. With the help of members here I restored my 400 starting during the COVID lock down.

I've had sleepless night during my first rebuild but it has not put me off doing a second despite a few heath issues getting in the way. If your mechanical knowledge is basic now is the time to learn - even more so if like me you are retired.

If it all goes belly up you can send the engine to Bryanj. Take plenty of photos as you strip the bike down, get hold of a Haynes Manual and go for it. Plus download the Honda Manual in Aladdins Cave or Asks dropbox. A parts manual is almost as good as a workshop manual or better for showing how the bike is assembled.

If you get stuck this is the site to help you out. If a bloke built it in Japan I'm pretty sure a Shetlander can fix it.👍👍👍

Title: Re: Opening that can of worms
Post by: Shetland Biker on April 06, 2024, 10:15:18 AM

Quote from: McCabe-Thiele (Ted) on April 05, 2024, 09:04:40 PM

I don't know your age or mechanical demographic but I'm with DomP on this one.
My only reservation is the 750 engine is pretty heavy so you will probably need a hand to lift it out.

I was 72 when I fully dismantled my 400 having done nothing on a motor cycle engine since I was a teenager. With the help of members here I restored my 400 starting during the COVID lock down.

I've had sleepless night during my first rebuild but it has not put me off doing a second despite a few heath issues getting in the way. If your mechanical knowledge is basic now is the time to learn - even more so if like me you are retired.

If it all goes belly up you can send the engine to Bryanj. Take plenty of photos as you strip the bike down, get hold of a Haynes Manual and go for it. Plus download the Honda Manual in Aladdins Cave or Asks dropbox. A parts manual is almost as good as a workshop manual or better for showing how the bike is assembled.

If you get stuck this is the site to help you out. If a bloke built it in Japan I'm pretty sure a Shetlander can fix it.👍👍👍

i would love to do it myself but i know its way above what i am capable of and it way way way out of my comfort zone,  even just stripping and rebuilding the bike is gonna push me to new limts

Title: Re: Opening that can of worms
Post by: Spitfire on April 06, 2024, 10:35:41 AM

As an F1 and F2 owner I would say that is definately an F2 and looks like it has been well kept, like the others on this site I would go for it myself and do a top end strip down just to see what is going on in there.
As for taking the motor out do the laying the bike on it's side trick.

Cheers

Dennis

Title: Re: Opening that can of worms
Post by: Moorey on April 06, 2024, 11:04:54 AM

  If it is a 78 US model it will be a F3  This may help you Identify it.

 http://www.sohc4.com/cb750/cb750f/

Title: Re: Opening that can of worms
Post by: Bryanj on April 06, 2024, 11:17:45 AM

More likely an "old stock" bike, they did not sell that well an Honda was discounting the last of the F2 to dealers when the dohc came out in 78

Title: Re: Opening that can of worms
Post by: Shetland Biker on April 06, 2024, 11:36:26 AM

it is a UK model, i know that for sure.  just been out to the garage this morning to try and work out a game plan and to see what is missing/broken.  this is a long term project. so i just plan to buy things when there is spare money,  the fuel tank is missing a small bit of paint and has started to rust, so i want to get the tank off and properly resprayed.  the frame is in pretty good condition so once i get it all stripped i might just need a bit of tidying up,  all the chrome will need to be removed and boxed up to go to the mainland to get re-chromed.  wheels off and sorted,  who ever put in the clocks has hacked at the wiring so i think im just gonna put in a whole new loom then i shouldnt have any problems.  and like i said if im going to do it, i may as well do it properly.  overall im not worried how much money i put into it but it will be slow and steady.  im hoping by around september/october i would have enough money saved that i can get someone to hopefully strip and check the engine.

Title: Re: Opening that can of worms
Post by: Bryanj on April 06, 2024, 11:54:42 AM

Just so you know that seat has been modified as well.
It would be worth taking the engine out and removing the head so you can determine which model top end it is, it is no problem running an earlier top end as long as oil returns are sorted, slightly down on power but are you really going to be able to tell unless you rag it everywhere?
If you want i can give you a mobile number to call me when i am sat at work on an evening so i can give you things to look for.
Good luck with the project

Title: Re: Opening that can of worms
Post by: Shetland Biker on April 06, 2024, 11:56:21 AM

Quote from: Bryanj on April 06, 2024, 11:54:42 AM

Just so you know that seat has been modified as well.
It would be worth taking the engine out and removing the head so you can determine which model top end it is, it is no problem running an earlier top end as long as oil returns are sorted, slightly down on power but are you really going to be able to tell unless you rag it everywhere?
If you want i can give you a mobile number to call me when i am sat at work on an evening so i can give you things to look for.
Good luck with the project

yea if you want to shoot me a message with your number that would be helpful,  thank you

Title: Re: Opening that can of worms
Post by: K2-K6 on April 06, 2024, 02:33:35 PM

Tentatively, looks like it may have the unique to F2 oil cooler plate behind filter housing (can't quite see in picture) which could mean F2 bottom end, or fitted to replacement engine as it's just a longer bolt used. Engine number will show case type anyway.

Top  "shelf" of head fins look more like K series as the F2 extended out more toward front wheelmin giving more cooling to exhaust port area.

As Bryan notes, could be K top onto F2 bottom end .... or K painted black to look like F2 original.

Title: Re: Opening that can of worms
Post by: Shetland Biker on April 09, 2024, 06:32:42 PM

so i have been in the garage for half an hour or so tonight,  started stripping down the rear end, only because that looked the easiest,  starting to get a bit more of an idea what parts i am definentely going to need, and what parts can be reused.  ideally i need to get all the bits off that need sent away to be rechromed,  all the frame black parts i am just going to clean up and rattle can,  the frame will only need touching up in places.  not 100% sure what i am going to do with the wheels yet.  the engine is still an issue too,  a lot of the engine/clutch/gearbox covered have been removed before i got the bike and i dont have the bolts that holds them all on,  so if anyone can recommend a bolt set with alan key heads that will come in handy that would be great.  i will order a box of M6 and M8 bolts in different sizes so i can change ones out as i put it all back together.  the more i look at it and as bits come off im getting less and less scared lol 

Title: Re: Opening that can of worms
Post by: McCabe-Thiele (Ted) on April 09, 2024, 07:47:03 PM

Personally I prefer SS bolts to the Allen Key Headed ones. If you use AKH bolts on the top of the engine they hold water and fill up with dirt over time. Lots of sellers that do kits so you get a similar length replacements.

My 500 was already fitted with SS AKH bolts so to save on costs I just replaced the top casing ones. Not bothered about the side covers being AKH ones.

If you look in the parts book the part number contains data indicating the length and thread size in mm, not the thread pitch though. If you search here you will find previous  information. There is also a code for if the bolt was Chromed, BZP etc.

By looking in the parts manuals you can see the order of the parts for the clutch assembly order in conjunction with workshop manuals.

Hope you took plenty of photos as you dismantled stuff, easy to think you will remember how it went then months down the line doubt creeps in.

Title: Re: Opening that can of worms
Post by: Shetland Biker on April 09, 2024, 08:23:40 PM

Quote from: McCabe-Thiele (Ted) on April 09, 2024, 07:47:03 PM

Personally I prefer SS bolts to the Allen Key Headed ones. If you use AKH bolts on the top of the engine they hold water and fill up with dirt over time. Lots of sellers that do kits so you get a similar length replacements.

My 500 was already fitted with SS AKH bolts so to save on costs I just replaced the top casing ones. Not bothered about the side covers being AKH ones.

If you look in the parts book the part number contains data indicating the length and thread size in mm, not the thread pitch though. If you search here you will find previous  information. There is also a code for if the bolt was Chromed, BZP etc.

By looking in the parts manuals you can see the order of the parts for the clutch assembly order in conjunction with workshop manuals.

Hope you took plenty of photos as you dismantled stuff, easy to think you will remember how it went then months down the line doubt creeps in.

its all bigger stuff i have removed so far, so there will only be one way it can go back on,  is there a download-able parts manual, if so could you send me the link,  unfortunately some stuff was already stripped before i got the bike, so they will be a bit more tricky to put pack together, but i will get there slowly

Title: Re: Opening that can of worms
Post by: McCabe-Thiele (Ted) on April 09, 2024, 08:25:59 PM

Just go to Aladdins Cave or Ash's Drop box at the top of this site Menu - all downloadable.

If you use the search box you will also find lots of answers to questions.

Title: Re: Opening that can of worms
Post by: Bryanj on April 09, 2024, 09:42:07 PM

Not sure if the F2 is there but good parts diagrams at cmsnl just make sure you get the correct model