Topic: Garbage Rebuild

[torchmonkey]

I'm new to riding, just got my license this summer, haven't ridden since the course. Picked up this 1975 CB750f last week. Yeah, I know, it's a total piece of garbage, but, what better way to learn than a total rebuild. Looking to get this thing on the road by spring or early summer 2010, lots of work ahead. Planning on some custom stuff. I'm loving Deus Ex Machina, Wrenchmonkees and Bratstyle stuff. Below you will find images of my beater in various states of disrepair since becoming it's proud new owner.








I want to thank all of you who have been so patient and helpful with a complete and total newbie to motorcycles, without your help I cuouldn't have gotten as far as I have already.

[torchmonkey]

Oh, I'm have great difficulty getting the pistons free of the cylinders. Pistons 1 and 4 are frozen,any advice would be greatly appreciated. They are currently soaking in a bath of PB Blaster and will be until I have a better solution.

[torchmonkey]

Have you scoped my dope exhaust??? I'm thinking about keeping it.

[camelman]

Total dopeness on the exhaust.  I was scopin'... and jealous.

Good luck with it, and keep up the good fight.  You'll get plenty of good advice on this forum.  By the way, are the exhaust ports clogged?

Camelman

[MCRider]

Oh, I'm have great difficulty getting the pistons free of the cylinders. Pistons 1 and 4 are frozen,any advice would be greatly appreciated. They are currently soaking in a bath of PB Blaster and will be until I have a better solution.

A better "solution"    is 50/50 Acetone (available from hardware, Lowes, etc in paint dept) and ATF (from auto supply. There is a study of penetrants on this forum somewhere that has this mixture as a better penetrant than PB Blaster (which I like BTW) and any other by a factor of 2 or more. So if the PB doesn't work you've got one more step.

Judging by the condition of the bike, its not hard to believe that your piston rings are rusted to the cylinder walls, A good soak and some wailing is called for. Use a 2x2 or whatever fits (closet rod) to whack the tops of the pistons. Don't hit them directly with a hammer unless last resort.

Something may break, like the pistons, but you have little choice. It would be nice if they come lose tapping on top of wood, as you don't want to transfer a lot of shock to connecting rods and their bearings. But this has happened to others here, maybe they'll chime in.

There is a big nut holding the alternator rotor on. (behind big cover, lower left front of engine) YOu can get a big wrench on it with a cheater bar and maybe break everything free trying to turn that.

[torchmonkey]

A couple had some caked-up white powdery mess in them, 3 stuck valves etc.. I think its been sitting since 83, last Registration sticker on the bike says so. Head is off taking it to work in the morning for a full refurb, got a couple bros who know whats up. I'm loving the adventure already, my wife is just stoked I didn't spend 10K on a Harley/ Ducati/ Triumph!

[MCRider]

A couple had some caked-up white powdery mess in them, 3 stuck valves etc.. I think its been sitting since 83, last Registration sticker on the bike says so. Head is off taking it to work in the morning for a full refurb, got a couple bros who know whats up. I'm loving the adventure already, my wife is just stoked I didn't spend 10K on a Harley/ Ducati/ Triumph!

From the looks of it, you'll have a couple grand in this by the time its done. Of course there's no topside limit. But you'll need a tank I think, wheel bearings, tires, suspension work, all besides the engine.

I've seen 25 yr olds in much better shape, where was yours left sitting. Looks like a boat anchor. And I mean that in the nicest way.   

[torchmonkey]

No offense taken whatsoever. I could have spent the cash on a new or slightly used bike, but what I do with the rest of the winter?

[Alan F.]

It's not that bad.

[mystic_1]

Yup, I've seen worse.  That exhaust has to win some sort of award though 

You're gonna learn a lot, that's for sure.

mystic_1

[CycleRanger]

It's not that bad.

That's what I was thinking when I saw the first picture.
Then I saw the gas tank and it was just down hill from there....

Still, it is a fairly intact 750F!

[MacM2010]

The PO didn't tell you it was running last year, did he? 

I had a stuck piston in my 76F, and after a hell of a soaking in penetrating oil, it finally came loose.  PM porscheguy912 on here to find out exactly what he did. 

That said, the F0 and F1 are fine, fine bikes, and once it's done, you'll be a happy owner.  Plus, you'll know a whole lot of sh!t you didn't know before, which is always good.

Congrats!
Mac

[Henning]

That looks like a K1 or K2 motor in there. Round this part of the world, you never see an F  with the original motor, all have been replaced with K motors. Probably because all the F motors went bad.

Actually, you never see SOHC's period. I'm commenting based on the adds in the local Craiglist equivalent.

[MacM2010]

Nah, that's an early F.  There's hardly a difference between the F0/1 and the Ks, but the tops of the pistons in the pics match the defunct F piston I have sitting on my desk right here.  They're slightly different on top to increase the compression ratio.

F motors all went bad?  Why I oughta....

[Thor's Hammer!]

Nice project man.  Keep us updated with progress and pics along the way.

[BeSeeingYou]

Probably because all the F motors went bad.

That would be news to all of us 75/6 F owners.  But then again what would we know.

Anyways, it looks like you will have your hands full for awhile.  Was it stored in a swamp?   It will be interesting watching this one brought back from the dead.

[Henning]

Looks like I stand corrected.  Now please don't hunt me down and shoot me!

[torchmonkey]

Yeah, it's a piece of crap, I know, I think that's already been established, come to think of it I'm pretty sure I announced that in my first post.
Currently have the head off and at a shop that is going to look into grinding the valve seats. Three of them were pretty rusty, if those are pitted from rust and unsalvageable the project is over. I've found another identical bike for a great price. Probably going to pull the trigger on that one as it's condition is far better than this piece of sh!t.

[mystic_1]

If the head turns out to be unsalvageable, you'll at least have plenty of potential spare parts for the new bike

mystic_1

[torchmonkey]

My thoughts exactly.

[MCRider]

Yeah, it's a piece of crap, I know, I think that's already been established, come to think of it I'm pretty sure I announced that in my first post.
Currently have the head off and at a shop that is going to look into grinding the valve seats. Three of them were pretty rusty, if those are pitted from rust and unsalvageable the project is over. I've found another identical bike for a great price. Probably going to pull the trigger on that one as it's condition is far better than this piece of sh!t.

If they are intakes, there are oversize valves for them but likely $$$. Oversize exhausts are usually not done as no improvement in power. They can be made but again $$$.

Rust is a b--ch

[BeSeeingYou]

I did not want to bring you down but I think you made a good choice in picking up the other one.  For $1500 you could find a nice running F or a decent project bike for much less.  That blue one is just too far gone to justify the expense unless you really like a challenge.    Try and salvage the rear master cylinder and caliper as they are hard to come by and would be worth making the effort.

[steamnjn23]

proceed slowly and deliberately. 
our project bike was wrecked, bent handlebars, broke spark advancer and points cover, apparently a pretty hard hit, looks like he may have rolled it. 
PO parked the bike in the weather.  tank full of water, carbs full of water, later evaporating causing white corrosion, the oil looked like chocolate milk, and the pistons were seized.

now its running, and will soon be road ready. 
just takes time, patience, dollars, and this site!

[BeSeeingYou]

Looks like I stand corrected.  Now please don't hunt me down and shoot me!

You're safe.   The F engines being bad gets thrown out there from time to time and we just have to keep shooting it down.  The 77/8 did have valve guide issues with premature wear but the 75/6 had no problems.

[Jerry Rxman Griffin aka MuthaF'er]

I did not want to bring you down but I think you made a good choice in picking up the other one.  For $1500 you could find a nice running F or a decent project bike for much less.  That blue one is just too far gone to justify the expense unless you really like a challenge.    Try and salvage the rear master cylinder and caliper as they are hard to come by and would be worth making the effort.

I'm with Steve on this. AND I'd like to know who you bought this from so I can kick his ass  

If that rear master cylinder is decent be SURE to save it. They only put them on the first 10686 F's. Even if it's unrepairable the nylon cup can be reused. I'd be interested in the blue seat trim if it's in good shape. Maybe some other pieces as well. Oh yeah, a decent wiring harness would be good to salvage and someone just asked me about the front electrical junction box.

I think you'd better really want to spend some serious cash, more than you think, on that bike plus I don't think you'd be ready to ride by spring. Sourcing parts will be your biggest constraint. Let us know what you're going to do and we can guide you about selling parts. I've been collecting parts for 3+ years for a full restore with total engine package and I can give you some really good advice on parts availability.

Hsserits aluded to the F engine. I do not believe they sold 4 years of F's in Europe like they did here, perhaps only 2 years. It's the 77 F2/78 F3 as they are know in the States that used the black engine with the valve angle problem. The 75 F & 76 F1 had the upgraded '76 and earlier K engine.