GS400/500 Gr650 Hybrid engine

[Guest]

Hello all,

My name is Rens, I'm new to this forum, I'm from the Netherlands but currently I'm living in Texas.
I have a 1981 GS450 which I am rebuilding to a café(ish) racer.


The idea is to have a GS400X bottom end, with the strong roller bearings and longer stroke.
This bottom end also has a kickstarter which will eliminate the electric starter, and battery, to save weight.
I will use a GS500 cylinder which does not fit just like that, I have to modify the upper crankcase.
On top of that, I will use a GR650 cylinder head which features bigger valves, better flowing and outward facing exhaust ports.
I found a GR650 cylinder head out of Germany, on Ebay.de, those things are rare, I will use the GS500 valve cover.

The engine I'm using was dirty and beat up by a "mechanic"; broken studs, sand on the inside etc. but it is in an incredibly good state, as in; low mileage.



So the bottom end is cleaned and all seals and bearings will be replaced, I gave it a nice shiny finish.



Now the first thing to do is modifying the crankcase so it will accept the bigger cylinder barrels



I will update my project soon as I already did the above, just forgot to take pictures.

My biggest issue with all this is the oil flow, the original GS400X oil pump is teeny tiny and I am going to run bigger high compression pistons, megacycle cams, extra oil cooler and I want it lubed properly.
Does anyone know if there is any pump interchangeable with the GS400X pump or whether I can fit different sprockets to change the gear ratio and make it spin faster.

And also, I'd like to remove the balancer shaft and drive gear all together, some people say do, some people say don't, the crankshaft is going to be lightened and rebalanced, so why wouldn't I?
I don't mind some vibration, it makes the bike feel more alive, as long as it doesn't hurt anything.

Rens

[Jedz123]

The GR650 Cams are the hottest for low to midrange power. I would love to utalize a 450 or 500 bottom end on my GR but the difference is huge south of the barrels. If I could turn my GR into a revy 650 that would be cool... Anyway running the GR650 Heads on GS500 Barrels and pistons will drop your compression... FYI but sounds like you have an idea what your doing here... I plan on following this one.

[Rensdw]

The GR650 Cams are the hottest for low to midrange power. I would love to utalize a 450 or 500 bottom end on my GR but the difference is huge south of the barrels. If I could turn my GR into a revy 650 that would be cool... Anyway running the GR650 Heads on GS500 Barrels and pistons will drop your compression... FYI but sounds like you have an idea what your doing here... I plan on following this one.

I'm planing on raising the compression to 10.5:1 either by using custom pistons or decking.
also i will use custom megacycle cams, i wont use the original 650 cams.

image.jpg

Now i have to figure out how to align those oil
passages and studs

[Rensdw]

image.jpg

So the crankcase accepts the bigger sleeves, these can be bored to gr650 size

[rapidray]

The cylinder stud spacing is the same on both?
Ray.

[Rensdw]

The cylinder stud spacing is the same on both?
Ray.

No, the stud spacing is different.

does anyone have a spare set of gr650 pistons?

[Jedz123]

I'm using mine... The tock GR 650 Pistons are dished I belive and stock GR650's have a pretty low compression ratio... FYI.

[Rensdw]

I'm using mine... The tock GR 650 Pistons are dished I belive and stock GR650's have a pretty low compression ratio... FYI.

You are using you spares?

Yes, they are 8,7:1 but if you deck the cylinder or change rod length you can up the compression, just have to take the valve-piston into account.
I might just make a mold and have custom pistons build

BTW: the end product will be 558CC

[hillsy]

So, how do you plan to line up the cylinder studs?

[Rensdw]

So, how do you plan to line up the cylinder studs?

I don't know yet, I think the way to go is weld it shut and re-drill the holes.
The two studs that feature the oil passages line up perfectly, they will not be changed.
The two studs opposite of the above have to move 1mm, I will machine some studs with an offset.
That leaves the four inner studs, they have to move a considerable amount, I would guess 4-5mm.
I might send the crankcase off to a guy I know that can determine the exact alloy and he can weld it accordingly.

It is much easier to modify the cylinder block to align the studs, but I like to be able to quickly change cylinders without too much machining.

Does anyone here have any experience with custom ceramic coatings on the pistons and cylinder head?
I'm worried about cooling, if I get my piston and head and maybe cylinder walls coated then cooling is no problem anymore.
Another benefit is that you then can ditch the oil cooler which will increase oil flow to the bearings.

And btw, did anyone notice that the RH crankshaft bearing is not lubricated by an oil passage? I'm thinking about drilling the hole and mount the same P/N bearing as the other three main bearings.

I will post a picture tomorrow that's shows how the studs have to be moved.

[robbiem1961]

hello my mate; we had a 1983 gsx 400 T seize and spin the shell bearing on the counter balance shaft; this left the crankcase damaged beyond economic repair; we had nothing to lose and working on the assumption that yamaha xs twins don't have a balance shaft we tapped and plugged the balance shaft oil feed galleries and rebuilt her minus the balance shaft; she did indeed fire into life; but it was very, very short lived; she did probably 5 or 6 miles gradually developing a MASSIVE knocking from the crankshaft area before stopping permanently; after this experiment we didn't bother to strip her down again and scrapped her; we had spoken to our local suzuki garage mechanics about our plan prior to our doing it and they had correctly foretold of our dismay; and then laughed heartily at our tale of confirmation;
I hope that this little nugget of information proves to be useful; be happier than a happy thing; cheers mate Robbie

[Rensdw]

Im planning to rebalance my crank to compensate for losing the balancer shaft.

here is a rough indication of how the studs need to move

image.jpg

[hillsy]

That's interesting that the outer studs are closer spaced on the 500 cylinder than the 425.

Looks like you have a bit of welding and machining to do.

[Rensdw]

That's interesting that the outer studs are closer spaced on the 500 cylinder than the 425.

Looks like you have a bit of welding and machining to do.

Indeed, when I bought all this stuff I assumed the 400X bottom end would be the same as the 450 and so the gs500 cylinders would just bolt on, I was wrong.
The crankcase is actually pretty different, the oil filter is in a completely different place for instance.

I'm thinking about experimenting with aluminum studs, I screw them down the four inner holes and mill the ends off, now I redrill the holes again in a different place.
Of course the aluminum studs will have very fine thread to make them strong and they will have Loctite on them.
The studs holding the cylinder down will be the original studs.
This way I can skip the whole welding thing, no heat damage, no warping and no extensive machining has to be done, And in my mind, it will still be strong enough.

If this works, it will be an easy. cheap and safe method to move studs around

[Joe Guilbeau]

So Rendsdw...where in Texas are you currently located?