750 Engine Replacement - What would you use?

[markfoggy]

Not saying it can't be done, just not exactly a bolt on job.

I've had it with W/C, too much of it.

Here's an old shot from about 2006 or so, I used to consider this to be the sort of thing that you should do to them. So many puncture wounds in fingers, but I never had one fail due to poor prep. This one is actually quite shit, I got a lot better than this.

Never again though, oil boiler for me, but I might do this sort of thing to an Oil Cooler

 

Probably 'cause I just can't help myself.

[markfoggy]

I'm Sorry, thread drift.

 

My Bad.

[Tony Nitrous]

On 7 January 2016 at 11:47 AM, Loud said:

 Here in Australia the majority of people chug around on late model 1000s 

I'd suggest you change the company you keep.

Folk certainly don't "chug around" on late model 1000's in Australia around here!

Heaps of 1100 / 1200 options. Enjoy the extra grunt and less stressed motor, turn up the pace and rev it like a 750 and get some real performance. If you want to rev the nuts off with less performance get a Jap home market 400.  

Edited January 8, 2016 by Tony Nitrous

[Loud]

22 hours ago, zookrick said:

If you want a real revvy top endy engine go for the 750 short stroke. I have a Teapot 750 with a header, GSXR cams, ported head and it screams, reminds me of my RM125 dirtbikes when I was a kid.

Did you use the original airbox for the motor?  One of the things that I love about the bike is being able to see the carbies, I've read that the short stroke motor can develop flat spots that aren't easily tuned out if the airbox is removed.

[zookrick]

2 hours ago, Loud said:

Did you use the original airbox for the motor?  One of the things that I love about the bike is being able to see the carbies, I've read that the short stroke motor can develop flat spots that aren't easily tuned out if the airbox is removed.

Yes, I am using the original airbox right now, if I upgrade the carbs I might go to pods.

[vizman]

cable ties and chicken wire.....I might ditch my job as an international egg sucking lecturer and join a race team

[HDTboy]

My 85 750 engine has a bit more compression, cams dialled in to kit timing, ports tidied up, carbs bored out to 32mm, and pod filters. It goes ok, suspension and frame bracing are the big things on a slabby.

[tabby59]

Well, I'll tell you what I did to my 86 750. I currently have  907 kit, Carillo rods, lightened balanced and polished crank, lighter starter clutch, RS38s, a fully ported 90 head with 28.5mm intake valves, Mega-Cycle/Yoshimura cams/springs, Hindle 4-2-1 exhaust, and a Dyna 2000 ignition. 142rwhp @ 12K rpm. Revvy? Yes. It scoots right along. I am the original owner and over the years when I get the itch, it gets more mods. It is really a simple question of how much you want to spend. If you look me up on Facebook{Tab Burgess}, look in my photo section. I have posted my dyno sheets and 1/4 mile time slips. It certainly isn't the be all, end all of old GSXRs, just my baby that I'll never sell.

Edited January 9, 2016 by tabby59
additions

[Loud]

Worthwhile posts, thank you gentlemen.

Tab, looks like the sort of engine I'd love, but like you it'd be one that would have to evolve over time.  I'll start having a look around to see what's available but it sounds like a '90ish head is a good starting point.  And I love the knee-dragging photos!  Did you make that rear engine brace?

HDT I think I've got the makings of a good suspension setup and I've got some pretty good pictures to provide to a reputable TIG welder.  As I'm not racing I'm not going to go too overboard, no double skinning for me!  What sort of compression are you running?

 

[HDTboy]

I haven't double skinned mine either. From the outside you need to look hard to see the bracing, mainly just closing up the cast sections, but also some triangulation through where the airbox would normally go.
I can't remember the exact compression numbers. I think roughly 1.1mm of squish. 2005 R1 shock fits with a bit of grinding, don't know how it works with the 1100 linkage ratio though, I have stock linkage, and a heavier spring on it's way here

[tabby59]

When I dropped my motor off at the shop that did the latest version of the motor, the owner{Rick Stetson} and I were talking about bracing. My frame is stock, but I doubled up on all of the mounting plates and eliminated the front rubber bushings. He reaches up on a shelf and hands me that brace. Apparently that was a somewhat popular brace years ago in the drag racing world. I honestly can't say if it made any serious difference,,,, certainly didn't hurt. I've considered more bracing, the usual stuff you see, but at my riding level, even on the track, she doesn't misbehave at all. I got my head off e-bay surprisingly enough. Everything was in good shape. The pistons in the 907 kit were made for 13.5cr. We both thought that was too high for practical street use and I wanted it to run fuss free on 93 oct. pump gas. So he took about .060" off the tops of the pistons. Compression is in the 11s. The head really looks like it was made for bigger valves and they put seats in for smaller intakes{27mm}. I could see and feel a small undercut in the head casting behind the seats. Rick also unshrouded the valves {massaged the chambers}. I have an 1100 linkage also, but with an Ohlins shock. The 1100 linkage has a different leverage ratio than the 750 and amazingly enough the spring rate that came with Ohlins is too stiff with that linkage. I looked up the spring rates of the Ohlins shocks that were made for the 750 and the 1100, and the 1100 does indeed use a softer spring. 

Edited January 9, 2016 by tabby59

[Loud]

Great info again thanks guys. 

I'll be hunting around for a rear shock made for my weight and to suit the bike.  I used a Nitron for my last build, I've never used an Ohlins and frankly couldn't justify the cost for my riding level.  I'll ask them to spring it for the 1100 by the sounds of things - was the dampening suitable Tab or would you suggest I look at softening that up too?

HDT I've seen plenty of pictures of bracing around the rear of the motor but  I can't rightly picture what you mean by "closing up the cast sections"?  I haven't yet stripped the bike to have a close look at the frame, any suggestions on what to look for?

I'm still tossing up whether to find a low km block or rebuild this one.  I've got a sneaky suspicion that it'll need a re-bore and that means Wiseco pistons and then it makes sense to get new rods, which all starts adding up.  Then there's the benefit of newer ancillaries like the starter motor, alternator, etc.

[tabby59]

I haven't dialed in my Ohlins yet to the 1100 spring. Going by the Ohlins spring chart, the 1100 spring is only one of their increments down from the spring used with their 750 shock. So I ordered the 1100 spring and the next increment down from that. That will be my next challenge, to get the 1100 linkage dialed in. I thought I'd just give you a heads up in case the bike doesn't behave like you would expect. Tomorrow I'll dig up the Ohlins numbers so you can have an idea of the rates that I am dealing with. I wouldn't worry about the starter motor or alternator. If they aren't totally toast, they should be fine. I have the original alternator and starter. New brushes and regulator on the alt at about 20K miles. The starter, I cleaned and regreased the bearings and polished the commutator{?}. They both have over 97K miles on them.

[HDTboy]

I've uploaded most of my build photos here There's one which shows most of the bracing, but even with it stripped bare you need to know what to look for

[tabby59]

OK, I'm back with some spring numbers. Yeah, this is supposed to be an engine thread, oh well. The only number I don't have is the OEM spring rate for the 750. If any of you fellows have that handy, please chime in. The 86-88 1100 OEM spring rate is 6.1 Kg/mm {340 lb/in}. The 86-88 1100 Ohlins shock/spring set {SU 635} uses their 1095-21 spring {180mm long} which is a 7.65 Kg/mm {428 lb/in} rate. So, here you can see how much firmer a spring over OEM Ohlins chose. The 750 Ohlins shock/spring set {SU 5274} uses their 1092-24 spring{170mm long} which is a 8.15 Kg/mm {457 lb/in}. Now you can see why my "seat of the pants" was screaming that the rear end was too stiff when I went to the 1100 linkage. The higher spring rate for the 750 pretty much confirmed to me that the bikes used different leverage ratios in the linkages. Not being a mechanical engineer, and being a bit lazy, I haven't tried to figure out those ratios. I just needed to confirm that there was a difference. I mean,,,,, why would you put a softer spring on a heavier bike if all else was the same?  So like I said earlier, I ordered the 1092-21 and 1092-19 {7.14Kg/mm or 400 lb/in}. 1095 is the length {180mm}, 1092 {170mm}. I ordered the one increment softer spring {-19} just in case the actual lighter weight of the bike using the 1100 linkage made the -21 spring a bit too much even. 

[Loud]

Tab that's brilliant, that's going to help save me some money from a mistake I would have made upon ordering the new shock.  Thank you.  I guess I do need to be a bit rude and ask how much you weigh though!  I'm ~90kg so it would help determine if your spring experience is relevant to someone of my weight too

HDT boy the pictures from your build have been very helpful - I've saved them with some others in order to show the welder what I need to have done to the frame.

I was pretty close to abandoning this forum given the initial droll response, it's great to know that there is help and worthwhile information from newer members such as yourselves who haven't built huge post counts from being... well, you know

I'm scouring Gumtree (our version of Craigslist) and Eblag for engine parts, to see what comes up that might be useful for the rebuild.  I'm kinda hoping that a modded 750 engine comes up, for a strip/inspection/reassembly.  I'll let you know how I get on!

[vizman]

glad you stuck around, but feel free to fuck off

[vizman]

3 hours ago, vizman said:

glad you stuck around, but feel free to fuck off

sorry, that should read 'I'm glad you stuck around, but feel free to leave' in response to your 'i was pretty close to abandoning this forum given the initial droll'

same sentiment but possibly more polite....? I'm not sure, just trying to bump up my post count to make myself feel special.....

[KATANAMANGLER]

8 hours ago, Loud said:

I was pretty close to abandoning this forum given the initial droll response, it's great to know that there is help and worthwhile information from newer members such as yourselves who haven't built huge post counts from being... well, you know

You get that one for free. Any more and you're gone. Capeesh ?

[Loud]

2 hours ago, KATANAMANGLER said:

You get that one for free. Any more and you're gone. Capeesh ?

Sounds like you've made me an offer I can't refuse.  

Edited January 11, 2016 by Loud

[vizman]

you wouldn't want to wake up with a dot head in the bottom of your bed.....

....glad to see you've stuck around Loud.

[Bandit31]

I do like happy endings.... 

Edited January 11, 2016 by Bandit31
spelling

[Captain Chaos]

this aint over yet.... we've just started taking the piss giving advise

[tabby59]

18 hours ago, Loud said:

Tab that's brilliant, that's going to help save me some money from a mistake I would have made upon ordering the new shock.  Thank you.  I guess I do need to be a bit rude and ask how much you weigh though!  I'm ~90kg so it would help determine if your spring experience is relevant to someone of my weight too

HDT boy the pictures from your build have been very helpful - I've saved them with some others in order to show the welder what I need to have done to the frame.

I was pretty close to abandoning this forum given the initial droll response, it's great to know that there is help and worthwhile information from newer members such as yourselves who haven't built huge post counts from being... well, you know

I'm scouring Gumtree (our version of Craigslist) and Eblag for engine parts, to see what comes up that might be useful for the rebuild.  I'm kinda hoping that a modded 750 engine comes up, for a strip/inspection/reassembly.  I'll let you know how I get on!

Hey Loud, in full racing leathers, helmet, gloves, boots and back protector, I weigh 195lbs. You may want a more specific rate than I do{so far}, I at least wanted to give you an idea of what ball park the rates are in.

[Loud]

On 11/1/2016 at 6:18 AM, tabby59 said:

Hey Loud, in full racing leathers, helmet, gloves, boots and back protector, I weigh 195lbs. You may want a more specific rate than I do{so far}, I at least wanted to give you an idea of what ball park the rates are in.

Hi Tab,

Just wanted to check and see how you went with your new springs?  I've just placed an order with Nitron (couldn't spring for an Ohlins!) and I'd like to try and get somewhere near the right spring to begin with - although they will swap undamaged springs for free (postage to and from the UK would add up though).

A bit of additional information that I found interesting, Nitron stated that the valving for the 1100 and 750 was "not too dissimilar" and with the new link "will be fine regardless of the spring rate".  Excellent

Back on topic - I ended up buying a '91 750 engine from Germany.  Despite being a long stroke version of the 750 it appears it actually revs as high as the short stroke 750 due to the later pattern con-rods and lighter pistons.  Instead of press-in bolts with nuts that earlier bikes featured the newer rods are basically the same as current bikes, meaning rod bolts screw in to threads in the con rod itself.  As a bonus I get a head with a more efficient combustion chamber than previous models as well as a shiim style head with independent cam followers.  The down side is that I can't run too aggressive a cam for fear of the shims "tiddly-wink-ing" out, although cams aren't readily available for this comparatively rare head anyway.

P.S. Thanks for the ribbing, one and all