77-81 interchangable parts?

[Jelloelstone]

I want a kickstart bottom end for my bobber. I currently have a complete 81 gs400. I have a bike yard near me that has a 77, 78 and 79 gs400 all with kickstart. Now i have no idea if they are siezed or not, if not, ill fix one of those motors, is so i was thinking of using the 81 top end. Is this possible?

[Mekanix]

What engine do you have ?

Is yours a 2 or 4 valve per cylinder engine ?

I wasn't aware there was a 2 valve 400 in 1981. I thought anything 400cc from 1980 on was a gsx400 with 4 valves per cylinder. adding kickstart is possible on the gsx400 and gs450 base. You need at least the starter gear and sidecover. And it would involve splitting the case.

[pete]

What engine do you have ?

Is yours a 2 or 4 valve per cylinder engine ?

I wasn't aware there was a 2 valve 400 in 1981. I thought anything 400cc from 1980 on was a gsx400 with 4 valves per cylinder. adding kickstart is possible on the gsx400 and gs450 base. You need at least the starter gear and sidecover. And it would involve splitting the case.

Come on, more details

I've seen that question asked so many times but never seen a "yes this is how" answer...

[Jelloelstone]

It's 2 valve per cylinder. Im gunna go to the bike yard tommorrow to see if the engine is worth it, i would really like a kickstart!!!

[Mekanix]

ok, From comparing two manuals, the case either has the provisions for the kick-start assembly or it doesn't. So its really dependent on the engine type.

If it was a 4 valve per cylinder then the answer is no.

But a two valve with roller bearings has the provisions to bolt the mechanism in place.

The clymer manual shows the whole kick-start assembly and how the case is made to receive it. It is focused on the two valve roller bearing engine.

The Haynes manual focuses mainly on the plain bearing 4valve engine and the case is not machined to allow the kick-start assembly to be installed.


By taking the side cover off you can see at the back of the case just above the gear selector, 3 threaded holes and one large hole in the middle. that means its possible.

If its just plain, as in no extra casting at all then its not Easy to make it work. You could do it but it would involve drilling a few holes and you have to be accurate so the side cover lines up .


hope that helps clear it up a bit

[pete]

ok, From comparing two manuals, the case either has the provisions for the kick-start assembly or it doesn't. So its really dependent on the engine type.

If it was a 4 valve per cylinder then the answer is no.

But a two valve with roller bearings has the provisions to bolt the mechanism in place.

The clymer manual shows the whole kick-start assembly and how the case is made to receive it. It is focused on the two valve roller bearing engine.

The Haynes manual focuses mainly on the plain bearing 4valve engine and the case is not machined to allow the kick-start assembly to be installed.


By taking the side cover off you can see at the back of the case just above the gear selector, 3 threaded holes and one large hole in the middle. that means its possible.

If its just plain, as in no extra casting at all then its not Easy to make it work. You could do it but it would involve drilling a few holes and you have to be accurate so the side cover lines up .


hope that helps clear it up a bit

Ok what you say there sort of makes sense to me (have never seen a 400 with a kick start in person), but I'm pretty sure it's the 2 valvers that have the plain bearing and the 4 valvers that have the roller bearings... isn't it? So the reverse of what you have there?

I'm pretty sure this is right based on my 450 being a 2 valver and it definitely has a plain bearing bottom end...

[Jelloelstone]

ill take a look to see if its possible right now! Too the bike cave

[7981GS]

Ok what you say there sort of makes sense to me (have never seen a 400 with a kick start in person),
but I'm pretty sure it's the 2 valvers that have the plain bearing and the 4 valvers that have the roller bearings... isn't it? So the reverse of what you have there?

I'm pretty sure this is right based on my 450 being a 2 valver and it definitely has a plain bearing bottom end...

It is my understanding that only the 400 and 425's came with roller mains.
All of the 450's came with plain bearing mains.

Daniel

[Mekanix]

+1 Daniel,

but I'm pretty sure it's the 2 valvers that have the plain bearing and the 4 valvers that have the roller bearings... isn't it? So the reverse of what you have there?

On the twins its all plain and all the same base after late 1980. Roller bearings were a previous generation of engine.

However the 4 cylinders were mixed between plain and roller, Some are plain with 2 or 4 valve and some are roller with 2 or 4 valve. It gets engine specific for those but the twins can be assumed to be plain unless they were made before 1980.


400's 77-mid 80s 2 valve were all roller bearing and had a unique case design. They do not swap parts well with the next generation of plain bearing engines and do not fit the frames without modifications.

400cc late 80's on were all plain bearings and the 400cc became known for being a gsx400.

However you could use the cylinder from a gsx400 and pistons from a gs750 and the head of a gs450 to make a 2 valve gs400. Just saying it is possible and easy to do.


425cc were not widely made after 80. This engine is a roller engine with a stroke of 60mm and bore of 67mm.


The 4 valve per cylinders are all plain bearing and the base is identical to the 450's and 500cc.

they all have the same transmission, clutch, crank, rods... all the base parts are shared.
They all have a 56.6mm stroke and the bore ranges from

67mm for a 400
up to 71/72 for a 450
and 75 for a 500.


This 1981 gs400 2 valve engine seems to be a mystery until I know if its plain bearing or not.

It could be roller and that would make sense. Suzuki could have just ran that model longer before shutting it down.

The plain bearing engines became the norm after that though.

[Mekanix]

found this http://www.youtube.com/watch?v=zWipZ...eature=related

show's the inside of a roller 400 2 valve engine quite well and shows the kick-starter.

[pete]

Ok... I *think* I am edumacated... maybe...

The models get very confusing and you do well to remember all that!

So looking at 0:38 in that video, you can clearly see the kickstart shaft and three bolts you're talking about, and as you can see by this they're gone by '82 on the 450's (this is mine) so no easy way for a kickstart:

[Jelloelstone]

It is a no on the kickstart to 81 engine. Now can i put the 81 topend onto the 79 bottom end?

[Mekanix]

Are they both rollers ? I don't think you said if yours was one or the other yet and that's what really makes the difference.

If so then yes.

If one is plain and the other is roller than not easily.


The difference is the stroke of both engines is different,

The plain engine has a stroke of 56.6mm
The roller has a stroke of 60mm

The connecting rod wrist-pin is 15mm diameter on the roller and 18mm on the plain engine.

The cylinder on a roller has elongated oil ports on the base
The plain engine uses the studs as oil channels.