GS 1000 engine in GSXR 1100 first gen frame?

[John Kat]

I stripped my GSXR frame today and...I got second thoughts about modifying it.
It's really beautifull engineering that went into it!
In fact it was clearly based on the XR 41 but on top of an aluminum frame it also got a lighter and more powerfull engine.
So why reverse engineer all that by putting an old GS 1000 engine in it???
Here's what it looks like:

 

[John Kat]

After cleaning up the frame a little, I positioned the GS 1000 cylinder head as close as possible to where it should go if the complete engine was in place.
In particular, I wanted to check the exhaust spacing and the overall height of the engine in the frame.
The conclusions are that there should be no issue on the exhaust side nor on the height side.
The only problem(?) seems related to the lower frame downtubes that will interfere with the lower engine case.
If this is really the case, it would considerably simplify fitting the engine as we would no longer have to extend the frame's top rails!
It would even be tempting to run an open craddle type of frame with the engine acting as a stressed member...
As there seems to be no 3D model of the GSXR first gen frame, I would greatly appreciate if someone had a GS 1000 lower engine case lying around that I could purchase?
I already have an upper case.
Here are the pictures and a link to a thread where a frenchman did the complete 3D model of the 2nd gen GSXR!

http://www.zimagez.com/zimage/1100gsxrkeyshot196.php

http://forum.airhuile.com/topic19462-1320.html

 

[John Kat]

Good news, today I positionned the upper engine case in the GSXR frame and it seems to fit like a glove.
One might have to grind away the small extension that's on the front right side of the upper case but else it's OK.
On the pictures you will see that the frame is tilted slightly forward with respect to the engine upper case to clear that extension.
If it had to remain in that position, the exhaut pipes would have to be (un)bent accordingly.
A small issue for the moment.
I checked the clearance for the cylinder head and it's OK.
For the lower engine case it's OK for the rear part but I need to check further for any interference with the front downtubes.
The other unknow is whether the lower case will fit into the existing frame mounting tabs???
Here are some pictures of the future XR 41...

 

[John Kat]

I finally got to the conclusion about getting the GS 1000 engine in the GSXR 1st gen frame: the frame is too short!
In fact you can get the engine in the frame by tilting it upwards in the front as you will see in the pictures but then the carbs will no longer fit...
Lowering the front of the engine in the frame requires an extension of 5 or 6 cm.
It's too bad because I believe the lower engine case would fit right into the frame's lower rear mounting lugs.
I will put the project on hold for the moment.

 

[Fjbj40]

Bummer! I had dreams of doing the same thing. I remember seeing a xr69 done using a bandit 1200.

 

[dorkburger]

........throttle bodies are smaller then carbs....far beyond my scope of knowledge, and not necessarily in the theme, but.......

 

[John Kat]

I finally gathered the courage to cut a GSXR 1100 G/H frame into two.
In fact, I found another frame without title to run this experiment.
Here are the two halves attached with a few strings just to get a feeling of what it would look like.
In one of the pictures, you will see the engine top case in place: it seems almost right?
The next question is to determine if I extend the top rails in a straight line ( that would help for carb spacing) or if I bend it slightly downwards to decrease the rake angle a little?
Any opinions?
PS: I'm still chasing for a lower engine case to complete the mock-up...

 

[steve murdoch]

This project is entirely out of my mechanical ability but i enjoy following along.
Keep at it, John.

 

[John Kat]

This project is entirely out of my mechanical ability but i enjoy following along.
Keep at it, John.

Thanks Steve!
This is what it looks like with the cylinder and head in place.
Tight but plenty of space for the carbs.
No issue with the exhaust port spacing.
Still missing the lower engine case...

 

[JTGS850GL]

Should be interesting once the lower case arrives. I'm betting that there's going to be some changes as a result. Looks to me like the engine is going to be raised slightly to clear the lower case on each side. Hard to tell but just going by the pictures. Interesting build.

 

[John Kat]

Should be interesting once the lower case arrives. I'm betting that there's going to be some changes as a result. Looks to me like the engine is going to be raised slightly to clear the lower case on each side. Hard to tell but just going by the pictures. Interesting build.

I agree, the engine might rise a little, in any case I know now why CAD/CAM is so usefull...

 

[kochic]

Nice project,
But why did you cut the upper portion?
You only have to modify the lower front portion of the frame to fit a gs1000 in a first gen gsxr frame.
Marc
http://www.thegsresources.com/_foru...ngine-in-a-first-ge-gsxr1100-frame&highlight=

 

[John Kat]

Nice project,
But why did you cut the upper portion?
You only have to modify the lower front portion of the frame to fit a gs1000 in a first gen gsxr frame.
Marc
http://www.thegsresources.com/_foru...ngine-in-a-first-ge-gsxr1100-frame&highlight=

I looked everywhere but never got to see one???

 

[John Kat]

I went through some basic maths to determine the best approach in lengthening the frame.
As the top rail has an angle of approximately 20? to the horizontal, if you separate the two frame halves top and bottom by 30 mm, one is faced by a step of 10.9 mm that has to be absorbed eitheir by the top or the bottom rail or by both.
Visually, one would see a Z in the frame rails.
Splitting the difference 50/50, I guess that with the tank in place the top Z of 5 mm would not be too noticeable while the bottom one would be hidden by the engine?

Another approach would be to extend the top rail by less than the bottom rail.
In this case it's possible to avoid the step on the top rail but this time the rail would be "bent" at the junction.
In a practical case the bend would reach 10? meaning that the rear end of the bike would be lower ( unless you use a longer shock).
This approach allows the bottom rails to meet each other with no offset but also at an angle.

The first modification is the easiest to implement as you don't need to compute the angles at which the rails will meet and the machining would be simpler.
Except for the wheelbase the geometry remains identical if the step is absorbed totally by the top rail.
If not the rake will increase unless the shock is made longer.
The second approach could be more aesthetic but more complex to compute and to machine.
In this case the rake will also increase.

I took another picture of the lower front rail positionned against a GS 1000 frame.
In fact the GSXR frame rails have a steeper angle going up to the tank but there is apparently no issue to take the bottom engine case.

 

[tatu]

I went through some basic maths to determine the best approach in lengthening the frame.
As the top rail has an angle of approximately 20? to the horizontal, if you separate the two frame halves top and bottom by 30 mm, one is faced by a step of 10.9 mm that has to be absorbed eitheir by the top or the bottom rail or by both.
Visually, one would see a Z in the frame rails.
Splitting the difference 50/50, I guess that with the tank in place the top Z of 5 mm would not be too noticeable while the bottom one would be hidden by the engine?

Another approach would be to extend the top rail by less than the bottom rail.
In this case it's possible to avoid the step on the top rail but this time the rail would be "bent" at the junction.
In a practical case the bend would reach 10? meaning that the rear end of the bike would be lower ( unless you use a longer shock).
This approach allows the bottom rails to meet each other with no offset but also at an angle.

The first modification is the easiest to implement as you don't need to compute the angles at which the rails will meet and the machining would be simpler.
Except for the wheelbase the geometry remains identical if the step is absorbed totally by the top rail.
If not the rake will increase unless the shock is made longer.
The second approach could be more aesthetic but more complex to compute and to machine.
In this case the rake will also increase.

I did wonder why you sawed straight through the middle, further back at the bend downwards would be the place, easier to join and brace and stronger, possibly using plate doublers that would blend in without notice, I dont know how the tank would fit, if you would have to remake mounting lugs to accommodate the 11mm?
I think the bottom rail cut further forward to stagger the joints too.
Just a thought.

 

[John Kat]

I did wonder why you sawed straight through the middle, further back at the bend downwards would be the place, easier to join and brace and stronger, possibly using plate doublers that would blend in without notice, I dont know how the tank would fit, if you would have to remake mounting lugs to accommodate the 11mm?
I think the bottom rail cut further forward to stagger the joints too.
Just a thought.

Hi Chris,
Yes, many options were open but reworking the junction between the longer top rails and the shorter rear verticals would be a nightmare as nothing is parallel.
Reworking the bottom rails is also a challenge as they only run parallel under the engine.
So far, with my approach, I don't need to touch the bottom rails except to extend them through a simple Z shaped bar.
I will go tomorrow to see my local machinist with my drawings for the extensions and see what he says.

 

[kochic]

This is a lot of work and I think its still a bad place to cut a old gsxr frame.Mesure twice but cut once.
The top section is the strongest part of the frame and these old frame where not remembered for their good road manner.
They drive like a powered hinge, my last one was a 1216 in a 86 gsxr 750 frame, flex is good.
I still have a 86 gsxr1100 frame and a gs1000 engine that are waiting to be mated together and again i will not touch the top section.
The swingarm pivot, steering stem and both axle will not be in the same place with the top portion modified.
Google old suzuki racing pictures and check what they have done to old gsxr frame.

Marc

 

[tatu]

Hi Chris,
Yes, many options were open but reworking the junction between the longer top rails and the shorter rear verticals would be a nightmare as nothing is parallel.
Reworking the bottom rails is also a challenge as they only run parallel under the engine.
So far, with my approach, I don't need to touch the bottom rails except to extend them through a simple Z shaped bar.
I will go tomorrow to see my local machinist with my drawings for the extensions and see what he says.

Is it too late to knock up a jig to steady the stem and swing arm points?

 

[John Kat]

This is a lot of work and I think its still a bad place to cut a old gsxr frame.Mesure twice but cut once.
The top section is the strongest part of the frame and these old frame where not remembered for their good road manner.
They drive like a powered hinge, my last one was a 1216 in a 86 gsxr 750 frame, flex is good.
I still have a 86 gsxr1100 frame and a gs1000 engine that are waiting to be mated together and again i will not touch the top section.
The swingarm pivot, steering stem and both axle will not be in the same place with the top portion modified.
Google old suzuki racing pictures and check what they have done to old gsxr frame.

Marc

There is a BIG difference in the section of the GSXR 750 and GSXR 1100 frame beams.
It's obviously a risk to cut the top beams but on the other hand, I'm going to weld the two hollow parts together with a solid part.
I don't have the skills to do a Finite Element Modeling of the structure but I'm sure the stress is far less on the top rail compared to the head stock.
My goal was to keep it simple so that it could be reproduced easily.
Also, the cost of machining special parts can quickly go beyond the price of most GS 1000's on the market.
I want to get myself an XR 41 for way less than an XR 69 from Harris...

 

[John Kat]

Is it too late to knock up a jig to steady the stem and swing arm points?

The way I've engineered the project will allow the frame to be assembled with a couple of bolts and then tack weld it on a jig.
I've also marked reference points on the frame before cutting it to make sure these references line up when reassembling it.