Jumped into the deep end

[MikeFlorendo]

New here, new to CB 750's and new to building bikes. I decided to have a project bike. Decided on a CB750 a few months back and just got one yesterday. Looks like a previous build. Found it in an impound lot. I dont know anything. I will learn as I go. If it takes me 3 years than so be it. I have 2 other modern bikes to ride.

Anyway, got the tank off. It's full of rust and crap but I think salvageable. Bought some Evaporust. Got the tank off and carbs are seized. Throttle body won't even move. Took the seat off. It was fabricated by Peter Chase of Cafe Cycles. I hit him up thinking might be his build but it's not. There is no oil in it and was covered in oil all underneath. That's as far as i got since yesterday.

Question, how do i know what seals to buy? Case has no numbers its obviously not stock because its not painted black. What year do yiu think the engine is? Does the tank really only stay on with the 2 rubber grommets in the front and a rubber piece at the back of the tank? I'll have 10,0000 more questions but thats good for now. Finally am i crazy or a stupid for taking this on with no knowledge? Here are picks

 

[dirtdigger]

Some quick looking I think it is a late 74 or K4 motor but could be up to a K8 model. Going to be hard to tell exactly without having the head off or at least the valve cover and maybe see some honda part numbers. Thats very odd that the case doesnt even have the cast space for the serial number...normally right behind the starter.

yes that is how the tank is held on.

Does the serial tag on the frame confirm that it was an actual super sport?

 

[MikeFlorendo]

Some quick looking I think it is a late 74 or K4 motor but could be up to a K8 model. Going to be hard to tell exactly without having the head off or at least the valve cover and maybe see some honda part numbers. Thats very odd that the case doesnt even have the cast space for the serial number...normally right behind the starter.

yes that is how the tank is held on.

Does the serial tag on the frame confirm that it was an actual super sport?

Yes, the f means super sport?

 

[Loki]

My guess is '77 CB750F2 because of the twin discs up front and the wheels, ah just seen your photo of the frame tag, if you look up the frame number that will confirm it, did you find the engine number, if so you can look that up as well and see if it matches the frame, it won't be the same so don't be misled.

Loki

 

[Loki]

For that frame number the engine number would be in the series starting CB750E-2600001 engine number is on the top of the gearcase beside the starter motor cover.

Loki

 

[MikeFlorendo]

For that frame number the engine number would be in the series starting CB750E-2600001 engine number is on the top of the gearcase beside the starter motor cover.

Loki

No numbers on the case. That's why I was wondering what year this motor might be. I'm super green and wasnt sure if there are tells from looking at it what year it might be. I guess I have to start pulling it apart. Thanks for the reply.

 

[dirtdigger]

Like said, engine is a K4 to K8 based on some external clues, gaskets are all the same unless it happens to have some hidden F2 parts which i doubt. Will be able to narrow down the year more once it is torn down but really doesnt make much difference just for gaskets. Pistons, rings, and some head parts are a different story but you will figure that out once you get down to that part.

 

[Loki]

I have a late F1 registered in 1977 but I think the 1977 F2 would have the engine painted black? so what you have is a K or an F1 but I thought the K exhaust clamped to stubs on the head rather than the bolt on finned rings on your engine? I'm a bit of a newbie on these but have learned a lot with this current project I'm doing and from other forum members. I have a bit of a build thread going on here if it helps you.

Loki

 

[MikeFlorendo]

Like said, engine is a K4 to K8 based on some external clues, gaskets are all the same unless it happens to have some hidden F2 parts which i doubt. Will be able to narrow down the year more once it is torn down but really doesnt make much difference just for gaskets. Pistons, rings, and some head parts are a different story but you will figure that out once you get down to that part.

Thanks! I'll order the gaskets and get the case off eventually and take some photos. Hit the carbs with WD40 to just get them moving. They move now but most likely need a rebuild. I will do a compression check now that the throttle opens. I'll post my findings. New battery on the way. Want to see if the electrical still works.

 

[MikeFlorendo]

I have a late F1 registered in 1977 but I think the 1977 F2 would have the engine painted black? so what you have is a K or an F1 but I thought the K exhaust clamped to stubs on the head rather than the bolt on finned rings on your engine? I'm a bit of a newbie on these but have learned a lot with this current project I'm doing and from other forum members. I have a bit of a build thread going on here if it helps you.

Loki

Thanks! I'll do a compression check this weekend. I pulled ones plug its brand new never been fired. Tells me that side at least was just put there to keep the elements out. Someone cared not to let dirt and water in. Ill pull the others and look at them.

 

[MikeFlorendo]

Like said, engine is a K4 to K8 based on some external clues, gaskets are all the same unless it happens to have some hidden F2 parts which i doubt. Will be able to narrow down the year more once it is torn down but really doesnt make much difference just for gaskets. Pistons, rings, and some head parts are a different story but you will figure that out once you get down to that part.

I'm cheap. Can I throw old oil in for the compression check? Im just going to kick it. Thanks

 

[dirtdigger]

What do you mean old oil? Kicking wont give accurate compression, you need a more steady constant speed of the starter to get accuracy and a good gauge.

I would hold off on ordering gaskets till its apart and you know what you need. Engine may be trash and you wont want to spend the money to build it correct.

 

[MikeFlorendo]

What do you mean old oil? Kicking wont give accurate compression, you need a more steady constant speed of the starter to get accuracy and a good gauge.

I would hold off on ordering gaskets till its apart and you know what you need. Engine may be trash and you wont want to spend the money to build it correct.

I meant used oil. I'll wait until my battery is delivered. Not sure if the starter even works. I guess I'll find out. The old battery won't even charge. Have it on a charger overnight and it's dead.

 

[dirtdigger]

I dont know how putting used oil in a possibly good engine would be a good thing. You risk damaging good parts with dirty oil.

 

[MikeFlorendo]

I dont know how putting used oil in a possibly good engine would be a good thing. You risk damaging good parts with dirty oil.

OK, thanks ill get new oil.

 

[MikeFlorendo]

Ignition looks good.

 

[MikeFlorendo]

Spark plug is new never been fired. Assuming it was placed in there to keep shit out.

 

[hinksy]

You might have a new bottom case motor due to a thrown chain . New replacements come without engine numbers , you can see the rectangle behind the starter on mine . Check the sump isnt full of oil , sometimes they will leak past the check valve and fill it when left for a long time . At least you should have less ignition problems with the dyna . I just did my tank in my 77F2 and I used evaporust when I first did it , but it came back . So I did vinegar the second time and all good so far . Check your valves mine had 29000 miles , it seems they have a bit of a fault from factory and can be floogged out . So mine looked like this

 

[dirtdigger]

The f engines had valve guides that wore early but the big problem was the valve spring retainers failed causing valves to drop into the cylinder. F engines need upgraded valve spring retainers.

 

[Loki]

The f engines had valve guides that wore early but the big problem was the valve spring retainers failed causing valves to drop into the cylinder. F engines need upgraded valve spring retainers.

Is there an upgrade for the valve guides? What would the upgrade be for the valve spring retainers? The engine is out of my F1 just now so would be a good time to do any engine work.

Thanks

Loki