1998 gsx750f to b12 conversion

[Maverik]

Further to my previous post about the b12 engine in a mk2 gsxf. Someone has suggested I just fit the b12 cylinder block and pistons to keep the 6 speed gearbox and better cams, which seems like an interesting idea. I have actually found a b12 block and pistons taken from a low mileage bike for a decent price. 

So, will it work? Do I need different rods? I understand the b12 is Bore x Stroke, 79 x 59 mm while the gsx750f is Bore/Stroke: 70.0mm x 48.7mm, nearly 10mm longer stroke which is what I expected but what I don't know is whether the pistons are physically taller or the rods need to be longer. I'm still very new to the idea of swapping in different bike parts coming from a gs500 that had very little scope for these kind of upgrades.

Obviously I'd still need the bandit exhaust downpipe, a new cam chain, head gasket, longer studs etc. But could I really just swap in a bandit block and pistons? If I can keep my existing head and cams it would be even better from a financial perspective but the idea of splitting the crank is a little daunting (I have done such work before but not on as big an engine, I had a two stroke for many years and the only time I split the crank on the 500 I got half way and decided I could no longer be bothered and bought a bigger bike )

[Upshotknothole]

Short answer, no. Long answer, with enough time and money and resources you can make anything work. Read through the archives for a better idea of what's easily modded with these engines and what takes some serious work. Check out the members projects as well.

If all you're looking for is more displacement and power out of your 750F, look for used 1100F power screen engines as well as used bandit engines. By the time you buy all the new gaskets, head studs, figure out your compression ratio and base gasket needed, and assuming the rods will work with the crank and the wrist pins, which I doubt without some modifications, you're probably going to be spending more money than just buying a stock engine and swapping it in will cost you. Also all the tappet head cams are interchangeable, so you can already use your 750F cams in a B12, just gotta swap the gears over.

And your little GS500 can be modded too, old mod for racing them was to use an oil cooled GSXR head and chop off cylinders 1 and 4 to make them a 4 valve head.

[Captain Chaos]

and the GR650 barrels + pistons fit on the 500 bottom.

[Maverik]

7 hours ago, Upshotknothole said:

Short answer, no. Long answer, with enough time and money and resources you can make anything work. Read through the archives for a better idea of what's easily modded with these engines and what takes some serious work. Check out the members projects as well.

If all you're looking for is more displacement and power out of your 750F, look for used 1100F power screen engines as well as used bandit engines. By the time you buy all the new gaskets, head studs, figure out your compression ratio and base gasket needed, and assuming the rods will work with the crank and the wrist pins, which I doubt without some modifications, you're probably going to be spending more money than just buying a stock engine and swapping it in will cost you. Also all the tappet head cams are interchangeable, so you can already use your 750F cams in a B12, just gotta swap the gears over.

And your little GS500 can be modded too, old mod for racing them was to use an oil cooled GSXR head and chop off cylinders 1 and 4 to make them a 4 valve head.

And this is why I come to these forums and ask daft questions. I might have thought about it in a few weeks time but you prompted me to check. The b12 big end bearings fit the sv650 and 650 gladius but not the 750.  So unless there's a 750 with a much longer stroke (unlikely given the mk2 750 already has a longer stroke/narrower bore compared to the earlier engine), as you say, the short answer is nope. No gonna work. 

Too bad. Would have like to keep the cable clutch 

[Captain Chaos]

B12 or 1100 engine can easily be converted to cable clutch. Use the sprocket cover from the 750 (pushrod length might need changing as well).

Edited August 16 by Captain Chaos
early morning spelling

[Maverik]

7 hours ago, Upshotknothole said:

Short answer, no. Long answer, with enough time and money and resources you can make anything work. Read through the archives for a better idea of what's easily modded with these engines and what takes some serious work. Check out the members projects as well.

If all you're looking for is more displacement and power out of your 750F, look for used 1100F power screen engines as well as used bandit engines. By the time you buy all the new gaskets, head studs, figure out your compression ratio and base gasket needed, and assuming the rods will work with the crank and the wrist pins, which I doubt without some modifications, you're probably going to be spending more money than just buying a stock engine and swapping it in will cost you. Also all the tappet head cams are interchangeable, so you can already use your 750F cams in a B12, just gotta swap the gears over.

And your little GS500 can be modded too, old mod for racing them was to use an oil cooled GSXR head and chop off cylinders 1 and 4 to make them a 4 valve head.

Do you have any idea what benefit there would be in using 750 cams in the 12? I'm not looking to steal a load of bottom and shove it to the top end. Horsepower is just a number, I'm a torque fan (I chose a tdi for a daily workhorse even though I don't really do the mileage to justify it). 

[Maverik]

4 minutes ago, Captain Chaos said:

B12 or 1100 engine can easily be converted to cable clutch. Use the sprocket cover from the 750 (pushrod length might need changing as well).

I wondered if that was an option. One of the b12 engines I've been looking at is missing the clutch slave.

I'm using parts from the gs to make a naked bike out if the 750, including the brake and clutch assemblies with built in mirror mounts 

[Upshotknothole]

4 minutes ago, Maverik said:

Do you have any idea what benefit there would be in using 750 cams in the 12? I'm not looking to steal a load of bottom and shove it to the top end. Horsepower is just a number, I'm a torque fan (I chose a tdi for a daily workhorse even though I don't really do the mileage to justify it). 

Blandits tend to be mainly bottom end power, GSXRs are all top end power, and the F cams were usually the best of both worlds for sport touring.

[Upshotknothole]

1 minute ago, Maverik said:

I wondered if that was an option. One of the b12 engines I've been looking at is missing the clutch slave.

I'm using parts from the gs to make a naked bike out if the 750, including the brake and clutch assemblies with built in mirror mounts 

The GS clutch perch should work. Not sure what year GS500 you have or which M/C it has, if the mirror mount is on the clamp, that should work with the 750F M/C, but do not use the GS500 M/C with the 750F brakes, especially if you're going to put a B12 engine in it. GS500s only had a single 2 piston front caliper, that M/C is way too small to work with any real brake setup.

[Maverik]

39 minutes ago, Upshotknothole said:

The GS clutch perch should work. Not sure what year GS500 you have or which M/C it has, if the mirror mount is on the clamp, that should work with the 750F M/C, but do not use the GS500 M/C with the 750F brakes, especially if you're going to put a B12 engine in it. GS500s only had a single 2 piston front caliper, that M/C is way too small to work with any real brake setup.

Oh christ no, the gs brakes are not ideal at all. I'm mostly using the headlight, mirrors, indicators, stubby brake and clutch levers, heated grips, and whatever else I can think of that could be transferable. If I come across a bandit donor I'll just swap the front end flog the 500 bits. Nothing of the engine, suspension or brakes will be used though. 

Balance of power and torque sounds good. I did choose the mk2 750 over the more powerful mk1 for it's improved midrange power. 

[clivegto]

The 750j/k can be converted it's all in frankinsteen pages on hear. 

[Maverik]

2 hours ago, Upshotknothole said:

The GS clutch perch should work. Not sure what year GS500 you have or which M/C it has, if the mirror mount is on the clamp, that should work with the 750F M/C, but do not use the GS500 M/C with the 750F brakes, especially if you're going to put a B12 engine in it. GS500s only had a single 2 piston front caliper, that M/C is way too small to work with any real brake setup.

I misread earlier. The master cylinders look almost identical but realistically I'll probably just look for brake and clutch masters from a mk1 as they have mirror mounts. 

[Maverik]

On 8/16/2024 at 7:50 AM, Upshotknothole said:

The GS clutch perch should work. Not sure what year GS500 you have or which M/C it has, if the mirror mount is on the clamp, that should work with the 750F M/C, but do not use the GS500 M/C with the 750F brakes, especially if you're going to put a B12 engine in it. GS500s only had a single 2 piston front caliper, that M/C is way too small to work with any real brake setup.

You were right, the mirror mount was on the clamp and was a straight swap onto the 750 m/c

[Maverik]

So I've been thinking to start sourcing the "cheaper" accompanying parts that I'll need. As I know that the 750 exhaust headers won't fit the 1200, I've been wondering if the b12 headers would fit on the 750 until I have the time and money to do the b12 swap in it's entirety. Bearing in mind that the bike will be naked so fairing isn't an issue. I'd be hoping to sell the 750 headers, if I can ever get them off. 5 broken exhaust bolts and 2 seized headers so far....

[Upshotknothole]

B12 header will fit a 750, just hang low. Mind speed bumps and curbs, easy to dent them.

[Maverik]

1 minute ago, Upshotknothole said:

B12 header will fit a 750, just hang low. Mind speed bumps and curbs, easy to dent them.

Perfect. So it's not going to screw too much with the angle of the muffler or impair the centre stand (which I fully intend to keep, never liked the idea of not having one)?

 

[Upshotknothole]

I have no idea on the center stand, never had one and plan on keeping it that way. The angle of the muffler depends on the mid pipe and muffler you're using. When doing these engine swaps, the engine will fit and the carbs will fit, but there is still some test fitting of exhausts, possibly spacing the oil cooler out to clear the now higher header, muffler placement and mount, fuel tap clearance over the higher valve cover, rear lower engine mount size, etc.

Check the build threads, there are some teapots in there, should give you a better idea of what's in store. The oil cooled stuff are pretty easy bikes to swap engines on compared to other models, but there's usually a couple things that you'll have to sort out to make it all work.

When you do get a b12 engine, you can put studs in the head instead of using exhaust bolts, it'll save you some headaches in the future.

[DAZ]

11 minutes ago, Upshotknothole said:

When you do get a b12 engine, you can put studs in the head instead of using exhaust bolts, it'll save you some headaches in the future.

And if when you fit the studs you use brass nuts ,they won't rust onto the studs and are soft enough not to strip the threads off the studs if  you over tighten them unlike stainless nuts.....

[Maverik]

1 minute ago, DAZ said:

And if when you fit the studs you use brass nuts ,they won't rust onto the studs and are soft enough not to strip the threads off the studs if  you over tighten them unlike stainless nuts.....

Yeah good shout, I was just going to use stainless bolts as I have in my previous bike. 10 years and they came out easily with a bit of heat. 

[DAZ]

2 minutes ago, Maverik said:

Yeah good shout, I was just going to use stainless bolts as I have in my previous bike. 10 years and they came out easily with a bit of heat. 

Whatever works for you , I like studs where possible for stuff like exhaust headers or intakes on cars Etc that may be on and off relatively frequently as it reduces the risk of damaging the threads in a head casting , it's not suitable for every scenario but it's fine on headers just put them in after the motors in the frame to give yourself a little more wiggle room and less chance of scratching the paint or powder coat

[Upshotknothole]

2 minutes ago, DAZ said:

Whatever works for you , I like studs where possible for stuff like exhaust headers or intakes on cars Etc that may be on and off relatively frequently as it reduces the risk of damaging the threads in a head casting , it's not suitable for every scenario but it's fine on headers just put them in after the motors in the frame to give yourself a little more wiggle room and less chance of scratching the paint or powder coat

Same, and I hate trying to get the bolts in on 2 and 3.

[Maverik]

1 minute ago, DAZ said:

Whatever works for you , I like studs where possible for stuff like exhaust headers or intakes on cars Etc that may be on and off relatively frequently as it reduces the risk of damaging the threads in a head casting , it's not suitable for every scenario but it's fine on headers just put them in after the motors in the frame to give yourself a little more wiggle room and less chance of scratching the paint or powder coat

I remember many moons ago on a gp125, my grandad who was a retired mechanic replaced one of my knackered bolts with a stud and it kept coming loose. I've just never really trusted studs since then. But after the ordeal I've had today breaking 5 out of 8 bolts, studs may be the way forward. 

[DAZ]

Could have been a worn out thread but one word springs to mind ..... Locktite 

[TonyGee]

I just stick to the standard allen bolts but make sure i pull them out once a year for a clean,  if i rode through winter then every 6 months would do. 

[Maverik]

1 minute ago, TonyGee said:

I just stick to the standard allen bolts but make sure i pull them out once a year for a clean,  if i rode through winter then every 6 months would do. 

I have replacements already anyway, stainless obviously. My days of all weather commuting are long gone, I'm in construction so the bike is just a toy.