FRANKENHONDA II the 1982 DOHC CB 750F2 Build

CrabsAndCylinders said:

Damn, those brackets look fantastic!

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Cheers I'm looking at what needs to be done to convert the mill to a CNC , hopefully we can design and replicate some of his work

When I get home I'll see how it looks maybe I'll just anodise it clear


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Cookie said:

I'd see about centering the wing on that logo: it'd look more balanced. Otherwise it just kind of looks like a decal saying "Franken" was tacked on to original. My $0.02.

They're pretty slick otherwise though; I love that your brother was able to match the font so closely to original

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Yea when it's in the middle it just doesn't sit right with me so it will have to look tacked on

Next challenge is getting the paint to match and also getting him to replicate the blue stripes , and work out how to / whether or not to strip the front and rear fairing


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cb250nproject said:

Yea when it's in the middle it just doesn't sit right with me so it will have to look tacked on

Next challenge is getting the paint to match and also getting him to replicate the blue stripes , and work out how to / whether or not to strip the front and rear fairing


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I wouldn't move it to the middle but rather about 1/3 of the way from the front.

CrabsAndCylinders said:

I wouldn't move it to the middle but rather about 1/3 of the way from the front.

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Spoke to my brother he will make up a sample I'll compare the two


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Can anyone tell me what the original front and rear sprocket ratios were on the dohc 750s I want to get new ones but I'm not at home to count the teeth also how many links in the chain ?? Cheers in advance


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cb250nproject said:

Can anyone tell me what the original front and rear sprocket ratios were on the dohc 750s I want to get new ones but I'm not at home to count the teeth also how many links in the chain ?? Cheers in advance

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Yup!
Taken directly from the Honda Factory Service Manual, 1981 Addendum (there were no driveline changes in 1982):

CB750F and K ran 18 Front/46 Rear (2.555:1 ratio) with a 108 link, #530 chain.

CB750C was 18/43 (2.388:1) with 106 link, #530 chain (loses some acceleration, but better for cruising/touring).

I went to a 17/40 combination with a 106-link chain on my 750C. Almost the same ratio (within 1.5%), but the smaller sprockets were on sale and saved me about/40. Also, it was cheaper to buy a 110 link chain and shorten it, than to buy a 106-link.

Cookie said:

Yup!
Taken directly from the Honda Factory Service Manual, 1981 Addendum (there were no driveline changes in 1982):

CB750F and K ran 18 Front/46 Rear (2.555:1 ratio) with a 108 link, #530 chain.

CB750C was 18/43 (2.388:1) with 106 link, #530 chain (loses some acceleration, but better for cruising/touring).

I went to a 17/40 combination with a 106-link chain on my 750C. Almost the same ratio (within 1.5%), but the smaller sprockets were on sale and saved me about/40. Also, it was cheaper to buy a 110 link chain and shorten it, than to buy a 106-link.

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Awesome I think my rear hub is a k anyway as it's a spoked rim with a disc brake, the original rim was a cornstar and it actually runs a different sprocket I was a bit devo as I was going to reuse it

If you change to a lighter chain say a 520 does that effect the sprockets you can use ?


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Yea it does. 520/530 are both 5/8" long between the links, I believe 520 is narrower (thinner). Might have concerns fitting on stock-sized sprockets (but I've never tried).

If you run a 520 chain you have to run 520 sprockets

So got back from work and decided after a red eye I would try to work in the bike... apparently this was not such a good idea, thought I would tackle the caliper rebuild



So these were the original pistons pitted, scratched and rusted



Here are the new ones that arrived

First I installed the rubber seals in, There is a thicker one that is inserted into the lower groove



Through great skill and mastery I somehow managed to twist the seal as I installed it, after a little cursing and persistence I untwisted it.

I then installed the smaller seal

Then repeated for the other side

I then put a little grease on them



Next I replaced the bleed nipple

Then I installed the rubbers and hollow pin

Then this is the moment where I totally fucked up



Yep put the pistons in the wrong way didn't I .... face palm moment... so being a kid raised on magyver I thought to my self what would he do... so I tried connecting the old rear brake master cylinder and for some reason I can't get the pistons to move out ... currently at an in pass.

So rather than give you turned my attention to getting the motor back in the frame, as I moved the stand the motor fell off and this happened



I'm hoping it still seals otherwise I'll be in need of someone to weld then machine it ... not really what I was hoping for

In addition I scratched the engine paint a little luckily it's on a side cover that can be removed and painted

I tried laying the engine over

But by myself I'm one arm short of being able to put it back in I think I'll have to wait for some assistance ... unfortunately wifey is about 1 week from due so my number one apprentice is off

Another thing I noticed I need to replace these bolts that hold the engine cover on

Does anyone have a part number or know the proper name for these ?


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You dont need to replace the entire bolt - you just want new rubber grommets for them. You should always replace these grommets if you are replacing the gasket as they tension the cover down to make it seal.

Thanks Hillsy, Do you have a part number for the gromit or know exaclty what its called so i know what to order online ?

Number 9 in this schematic - they are called mounting rubbers - Honda part number is 90541-425-000

you are a god dam legend

order placed cheers Hillsy

Ok so I couldn't let it beat me so I concocted a plan on how to get these pistons out

So first I connected the reservoir for gsxr front calipers



Then I proceeded to purge the line of air first I disconnected the line from the caliper it took a little but the fluid started coming through.

Once I had fluid there I kept the lever down and reconnected the line to the caliper



Next I connected a clear line to the bleed valve and waited for the air to purge

Then I kept at it till there was movement on the pistons

I just kept resistance on both the pistons so they came put evenly



Success and now to undo my bad work and reinsert the pistons the correct way



Ok so next I had to put the pads back in each held in place with two pins


Once the pins are in there is a retaining plate that bolts into place


I then connected to the arm that secures it to the rear axle



Job done


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Ok so last night I managed to get down to the old mans with the frame so we could make up the final spacers required to fit the rearsets and also to make sure the brackets didn’t interfere with any of the bolts ( which they did a little)


So first we made sure the holes were in the right place.. the pressure was on as I was the one who made the template so if she was out it was on me, luckily she fit just like a bought one.

Once the brackets were finished n place we measured to see how big the spacers would need to be


The right side required a larger spacer for the bracket as the left side sits just about flush



We turned up the spacers for in between the rear set and the brackets first as they would be the same the two tops and then the two bottom spacers



Top spacer done



Top and bottom complete



This was the spacer for in between the frame and the bracket





Right side complete next issue was that the swing arm bolt was too long so it needed to be shortened and rethreaded... this is always a tense moment as we’ve found it’s really hard to undo or put back what you mess up :/



Fist the old man established the thread size, this then dictates the gearing of the lathe.



Then he did the scratch pass and we double checked to make sure we were on point... came up all good



Clearances were tight





So I’ve decided to leave it silver I think it would be a shame to anodise it black and not have the old mans craftsmanship stand out

...now I’ve got to work out how to get this engine in :/


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Well done; those rearsets are looking boss!

Looks slick man. Out of curiousity, why not continue the chamfer around the entire bracket? Noting seems to be mating that far out, and it may look a little cleaner. Just thinking out loud lol.

jag767 said:

Looks slick man. Out of curiousity, why not continue the chamfer around the entire bracket? Noting seems to be mating that far out, and it may look a little cleaner. Just thinking out loud lol.

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Because that’s the way the rear sets are chamfered, they are not chamfered around where the bolts are


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