1983 Honda 750 Nighthawk

[doc_rot]

Putting fresh upholstery in the sun is a common tactic by shops to make the material shrink fit tight. Every seat will do this but it depends on how tight you stretch the cover to start with and also how the seat pan is attached to the frame. Most seat pans only have a couple mounting points which let it taco. However if you attach the pan in a way that causes it to be pulled to the underlying structure, like fasterners around the perimeter you casn negate the effect of the cover shrinking with a dead flat pan.

I have made a couple fiberglass seat pans and the problem with those is that unless the resin is heat cured before stretching a cover the seat pan can move when it gets hot the first time as well. You end up having a multiplying effect where the seat cover gets hot and shrinks, it pulls the fiberglass seat pan which is soft from the heat and the whole thing goes taco. Then it cools this way, and its tough to undo. It doesn't move a huge amount. This happened to me with the first custom seat on my KZ1000, I ended up with about a 1/2" gap between the seat and the tail. This is not a huge gap by factory standards, but, dammit this shits custom, it needs a better fit. The last fiberglass seat pan I made I basically took a mold off a factory seat pan, so all the features of a factory seat pan were present in the fiberglass version, and this seat pan did not taco.

 

[chickenStripCharlie]

Well, it looks like this pan is going to be quite a bit more complex than I thought given the tank choice. The tank is off a 750c and doesnt have that nice lip like the f or k tank does. So I'm going with this front piece to take up the gap .... should provide more rigidity, too.

I should have used a bit bigger diameter pipe for my home-brew sheet metal brake die, but oh well .... we'll see

Trying to avoid the gap like this guy here has .... while I love his seat that gap really takes a lot away from it.

I'm guessing the seat he bought was for a k or f model where the front of the seat tucks nicely under the lip of the tank, but just doesnt work well with a 750c model tank

 

[chickenStripCharlie]

@teazer .... So, i took a gamble on the '99 GSXR calipers and lost ... kind of. Found a set being sold from within Canada, so couldnt pass them up.
The inside of the calipers ended up being thicker than i anticipated, and they don't clear the spokes. Again, a note to anyone doing this .... this is why people stay away from the "reverse comstar" wheels and go for the earlier comstars! They stick in more than can be ground off.

Now, my options are:
1. Bracket for current calipers - bolt a bracket to the OUTSIDE of fork. Bolt the caliper to the INSIDE of the bracket using 5mm spacers to bring the caliper in just enough, but not as far as stock location. Similar to pic below where they are using a bracket to adapt GSXR calipers to an SV650.
2. Different calipers - which won't match the 91mm bolt spacing and will need an adapter anyways ... plus the cost of yet another set of calipers.
3. Just get a GSXR wheel - Don't want to admit defeat and go this route just yet.

 

[teazer]

Key dimensions/parameters are where is the disk rotor relative to the spokes. That's where you have to start because the caliper has to be centered on the disk, so play with that first. Then see what the caliper to fork adapter has to look like.

If the rotor has to move out so far that it touches the fork slider, then that combo of triple trees, wheel and caliper will not work. With GSXR forks and triples that is unlikely to be a constraint in this case. Use washers to simulate the rotor spacers.

 

[Rider52]

Caliper size is a major problem with Harley to sport bike brake conversions. Can you shave a bit off the back side of the calipers? That is the common practice on the HD conversions. The solution I used on my Evo chopper was asking the EBay sellers to measure the calipers width. EBay is full of Tokico and Nissan calipers and it didn't take long to find one that worked for my application.

 

[irk miller]

Is there a reason for that specific Tokico 4 pot caliper? They make a two pot caliper that looks nearly identical and it's on a shit ton of different model bikes, so the replacement pads are uber plentiful. SV650 and GS500 are two of many bikes that came with this caliper.

 

[chickenStripCharlie]

Caliper size is a major problem with Harley to sport bike brake conversions. Can you shave a bit off the back side of the calipers? That is the common practice on the HD conversions. The solution I used on my Evo chopper was asking the EBay sellers to measure the calipers width. EBay is full of Tokico and Nissan calipers and it didn't take long to find one that worked for my application.

How much can one shave off, though? Unlike a car caliper, it seems like even taking off 2mm would be too much on the bike ones.

 

[chickenStripCharlie]

Is there a reason for that specific Tokico 4 pot caliper? They make a two pot caliper that looks nearly identical and it's on a shit ton of different model bikes, so the replacement pads are uber plentiful. SV650 and GS500 are two of many bikes that came with this caliper.

The reason was that it would bolt right up to the GSXR forks with its 91mm bolt spacing. Nothing else, really.
The ones in the picture are flat on the inside, and definitely a better option for this wheel, but with those i'd also have to now make adapters to fit the forks.

 

[Rider52]

How much can one shave off, though? Unlike a car caliper, it seems like even taking off 2mm would be too much on the bike ones.

You would have to measure the wall thickness.

 

[chickenStripCharlie]

You would have to measure the wall thickness.

Got any tips how to measure? With the piston out I dont have any tool that could measure accurately.
(If I assume thickness is uniform, I guess I can see if I can measure somewhere else).

It's definitely an option as well that I'm still considering. Would be the easiest, by far.

 

[irk miller]

Got any tips how to measure? With the piston out I dont have any tool that could measure accurately.
(If I assume thickness is uniform, I guess I can see if I can measure somewhere else).

It's definitely an option as well that I'm still considering. Would be the easiest, by far.

How I measure, is to place the caliper on a table with mounting holes in the correct orientation that the forks are. Usually this is level, but not always. Then measure from the mounting hole to the table surface (A). Then, measure the gap (B) between the same mounting hole to the rim face (or spokes). You're usually just measuring the bottom hole, since that is the hole that aligns with the thickest part of the wheel. With single sided calipers like I posted before, you need only minimal clearance, since braking pulls the caliper away from the rim. With the type you are using, I typically give it a little bigger gap. A-B= material to remove.

 

[cxman]

you can buy push back spacers for those caliper that will with an additional simple non structural angle cut on the edge of that caliper

provide ample clearance that step was missed in the cx write up

like these simple and easy

4X 10mm Aluminum Spacer Radial Brake Caliper For BMW Yamaha R1 R6 Suzuki GSXR | eBay

Our spacers have dowel locator on one end (dowels are mostly found on calipers of R1, R6 or suspension fork bottoms) and collar on the other. Those are used for caliper or disc conversions and will fit all calipers with M10 bolts as found on all radial calipers on BMW, Ducati, Suzuki, Kawasaki...

www.ebay.com

 

[chickenStripCharlie]

you can buy push back spacers for those caliper that will with an additional simple non structural angle cut on the edge of that caliper

provide ample clearance that step was missed in the cx write up

like these simple and easy

http://[URL]https://www.ebay.com/it...070364?hash=item5b70d5989c:g:tt8AAOSwDXpdCI0M

[/URL]

Hmmm, but my calipers are not radial mount. They are conventional. So adding spacers would push the caliper even MORE toward the wheel ... as they are mounted on the inside of the fork.

I think these might be used with radial mount calipers to run larger diameter rotors

 

[cxman]

oops sorry that front end does not have the radial calipers i will butt out now

 

[chickenStripCharlie]

How I measure, is to place the caliper on a table with mounting holes in the correct orientation that the forks are. Usually this is level, but not always. Then measure from the mounting hole to the table surface (A). Then, measure the gap (B) between the same mounting hole to the rim face (or spokes). You're usually just measuring the bottom hole, since that is the hole that aligns with the thickest part of the wheel. With single sided calipers like I posted before, you need only minimal clearance, since braking pulls the caliper away from the rim. With the type you are using, I typically give it a little bigger gap. A-B= material to remove.

Yeah, that part is easy, I meant measuring the actual thickness of the caliper to be able to tell how much can be taken off without compromising the strength of the caliper.

 

[irk miller]

Yeah, that part is easy, I meant measuring the actual thickness of the caliper to be able to tell how much can be taken off without compromising the strength of the caliper.

If you mean just for the specific calipers you posted as using, you have to take them apart and measure the depth of the bore and subtract for the easy measurement you already figured out. It's going to be an angled measurement for what you have to take of. A piece of wire or a screw driver or similar will get you close if you don't have a depth micrometer.

If your pic is any indication, I can't see how those calipers will work at all. Looks like you'll be cutting into the bore. Strength is going to be the least of your concern.

 

[chickenStripCharlie]

If you mean just for the specific calipers you posted as using, you have to take them apart and measure the depth of the bore and subtract for the easy measurement you already figured out. It's going to be an angled measurement for what you have to take of. A piece of wire or a screw driver or similar will get you close if you don't have a depth micrometer.

If your pic is any indication, I can't see how those calipers will work at all. Looks like you'll be cutting into the bore. Strength is going to be the least of your concern.

Yes, good eye. It's worth mentioning (from my previous thread about offset bearings) that my wheel is currently not centered. It needs to go another 2.5mm in the other direction, so the amount of interference you see there sould be reduced by about 2.5mm. So, it won't be quite as bad as that picture! I just worked on the side that had the least clearance for now to be in the "worst case scenario".

I will have to get my R spacer shortened by 2.5mm and get a new L spacer made up that is 2.5mm longer, then reassess.

Honestly, i think having the caliper mounting surface milled 2mm would solve my problem, but i'll have to talk to my machinist guy and see how much it would cost. Sometimes the setup for irregular shaped parts like this is where they spend most of their time.

Thanks everyone for the great advice so far. Keep it coming!! I love this forum!!

 

[chickenStripCharlie]

Just went to the garage to look at the calipers again.... I think it's definitely easiest to just mill down the mounting surface and bring the calipers out a bit. There is more than enough meat on there to mill down a couple of mm.

It will be much easier and cleaner than doing my own adapter. I'd have to make one out of 1/8" aluminum or so. Confirm all dimensions then get it CNC'd out of 3/8 or 1/4 al aluminum.

 

[chickenStripCharlie]

Took some more measurements and it looks like 4mm would have to be taken off to be safe. Call it 3mm and 1mm shaved off on the caliper itself.

What do you guys think. The mounting points of the caliper are 15mm and 12.3mm thick.

So removing 3mm is about 25%. That sounds like a lot. But 9mm of thickness left is still 0.366" which sounds plenty.

Thoughts?

 

[Streetfighterkz]

So removing 3mm is about 25%. That sounds like a lot. But 9mm of thickness left is still 0.366" which sounds plenty.

Thoughts?

What size mounting bolts are the calipers using: 8mm or 10mm? If they’re 8mm that’d be cutting it close as you want at least a 1:1 thread engagement ratio. In other words, you would want 8mm thread engagement for a 8mm bolt, 10 for 10, etc. For critical parts, I prefer 1.5:1 so 12 for 8....

Later, Doug