GSX400 to GS450 conversion

[John Park]

Well, it's done and in and running.

But… I suppose I should have paid more attention to potential foibles and pitfalls. The old rule of assume nothing applies, and any time you are grafting on anything other than the original parts you can run into the unexpected.

In this case it turned out to be the cam chain guides. They're a different part number, and I should have checked that. The good news is that the cam chain is the same 120 links, but you'd think it was different because it's tight to fit. The tensioner protrudes almost too far even when fully retracted so the knob doesn't really spin into adjustment. There's plenty of travel left in the guide though, so I decided to make a spacer out of extra thick gasket material and that gave me some movement.

It runs just fine. There may be some downside to not running the original guides, but the front looks almost identical although it's a different part number and easily changed. The slack side is more problematic as it's a split the cases proposition. The GSX 400 part is no longer available.

I'm going to machine a proper spacer about 3mm thick which should put the CCT in a more normal part of its stroke. As it is, the chain seems a bit whirry - but I'm not too whirried about it. I have another motor that I'll redo as well, and just split the cases and do bearings and a new guide. This one was just intended as a learning experience and to be a spare.

Despite the [slightly] used rings, the motor is tight and crisp and the rings seem to have seated right away. It has more low end grunt than the 4 valve, especially below 4K and pulls 6th up the local 'dyno hill' whereas the 400 petered out without a downshift. I haven't tested above 7500 yet, but I have a feeling that the frantic top end rush of the Twin Swirl will be more sedate like the old two valve 400s.

I don't think that I'll miss the GSX version. If I wanted a high revver I'd find a 400 Bandit.

If I don't reply, I'm out there breaking it in. Or blowing it up….

[tkent02]

OK, sounds good!! If a 450's cylinders and pistons fit, the 500's do too. Just for future reference.

[John Park]

OK, sounds good!! If a 450's cylinders and pistons fit, the 500's do too. Just for future reference.

Funny, but I had the same thought…..the bike reminds me somewhat of an old Triumph 500 C I used to rat about on in my misspent youth. The displacement would then match; minus the Lucasitis and vibration.

[tkent02]

Probably be a whole bunch faster and it wouldn't leak.

[John Park]

Probably be a whole bunch faster and it wouldn't leak.

Actually, mine didn't leak. Well, eventually it did decide to leak out the side of the cylinder after I bored it .060 oversize on the sleeved aluminum barrel - against the advice of the older and wiser experts. It lost power and my left leg got warm…..

The 'new' motor now has about 150 miles on it and runs fine. The whir appears to be gear whine from the primary drive. It's not excessive, but my other motor was almost silent by comparison. Probably just manufacturing tolerances, or too many miles on dirty automotive oil. It wasn't clean and pretty inside.

[tkent02]

Straight cut primary gears or are they helical?

[John Park]

Twins are all helical cut, which is a good thing if you hate the Honda whine. With a roller crank the side force is not a problem, but with a plain bearing crank you need to have a thrust bearing. and what they put in is rather dubious looking. The saving grace of it is that the center main is spewing endless amounts of oil at it so it works. I've heard of GS500s that are raced having endplay problems, but the typical 450 twin just works.

Usually, helicals are pretty much silent by design. That's why I'm suspicious. Maybe the tolerances are just a bit off on the shaft centers or whatever. But the gears look fine and the end play is within spec so I'll just get used to it. And it may go away; the motor sat for some time and maybe the cases dried out and shrank…….

[tkent02]

Well if a GS isn't making some funny noise somewhere it isn't running.

[GregT]

Twins are all helical cut, which is a good thing if you hate the Honda whine. With a roller crank the side force is not a problem, but with a plain bearing crank you need to have a thrust bearing. and what they put in is rather dubious looking. The saving grace of it is that the center main is spewing endless amounts of oil at it so it works. I've heard of GS500s that are raced having endplay problems, but the typical 450 twin just works.

Usually, helicals are pretty much silent by design. That's why I'm suspicious. Maybe the tolerances are just a bit off on the shaft centers or whatever. But the gears look fine and the end play is within spec so I'll just get used to it. And it may go away; the motor sat for some time and maybe the cases dried out and shrank…….

Never seen a problem with the half moon thrust bearings - either on fours or twins. Even the Hayabusa and the current GSXR1000 use the same setup.
I'd have a look at the gearbox mainshaft bearing behind the clutch. They're an angular contact bearing - or should be - and any pitting on the races will show as noise.

[John Park]

Never seen a problem with the half moon thrust bearings - either on fours or twins. Even the Hayabusa and the current GSXR1000 use the same setup.
I'd have a look at the gearbox mainshaft bearing behind the clutch. They're an angular contact bearing - or should be - and any pitting on the races will show as noise.

I've never seen a problem either, but somebody was having problems with them on a GS500 twin they were racing - also the counterbalance shaft bearings wearing quickly - but I lost the thread. They just look insufficient and have considerable load on them. On the other hand, the load is the result of constant torque and not going to rise exponentially like on a rod bearing.

I would have liked to see a full circle bearing which would better support a hydrodynamic wedge, but maybe it wouldn't oil as well. I'm just skittish about non full circle bearings after Honda's early XL 100 motors that had those cutouts for the cam lobes to pass through and had to be redesigned with a two piece head.

I'm not sure what the primary looks like on a GSXR, but I wouldn't expect they are helicals. Dunno; never looked. But even so, displacement isn't the determinant of load; at any given time the load is coming from one cylinder so a 250 single has the same instantaneous torque as a 1 liter four. But a four is constant so the heat generated is greater.

This isn't like bearing noise, but just a faint musical whine that sounds healthy. There's just more of it than on my other motor, but I did notice that there's less visible wear on these than on my other motor so maybe it will decrease over time. I'm just going through the different noises phase…..

[tkent02]

Whining gears, we had an old Toyota with a whining fifth gear, which started whining when it was run with no transmission oil for a little bit. The whine never went away, nor did it get worse. Nothing ever failed. Also had an Opel GT with a whining differential, which started when it was run dry, it actually seized up going up a hill. Let it cool, added oil, it was fine after that but always whined. Not sure exactly why this would make a gear whine but it sure did on that Toyota and that Opel.

Wonder if perhaps someone ran your engine without enough oil and it will whine forevermore?

[John Park]

Whining gears, we had an old Toyota with a whining fifth gear, which started whining when it was run with no transmission oil for a little bit. The whine never went away, nor did it get worse. Nothing ever failed. Also had an Opel GT with a whining differential, which started when it was run dry, it actually seized up going up a hill. Let it cool, added oil, it was fine after that but always whined. Not sure exactly why this would make a gear whine but it sure did on that Toyota and that Opel.

Wonder if perhaps someone ran your engine without enough oil and it will whine forevermore?

Evermore will probably be limited by factors other than the primary gears. I think you'd have major mechanical mishap in the crank and topend long before the lube to the primary got critical.

This motor only has to run until next spring.

[John Park]

It's stopped whining. I have no idea how long this block sat without running and the oil was old, sour, and filthy. Maybe it just needed some miles with fresh oil in it to smooth out.

Much as I found the 4 valve motor amusing, this version is much more practical. The GSX version has a frantic top end rush, but is rather marginal under 6K rpm. To it's credit, it gets better fuel economy and runs more sedately with less cammyness down low, but the 450 has more attitude and grunt. I'm more of a hemi head guy so it feels right to me.

Next winter I'll take my 'good' GSX 400 apart, check all the bearings and such, and put in a 450 guide, new chain and GS500 cylinder block. I'm not sold on the look of the 500 cylinders with the notch styling on the fins, but maybe painted black like oldBritish iron barrels it will look 'serious'.

From the look of it, the GS500 head no longer has the internal air passageway to feed the fins over the combustion chamber. Probably easier to cast and just as effective. Does the 500 cylinder block still have an air passage between the barrel and the cam chain tunnel or is it closed off? Paging T Kent...

[tkent02]

Can't remember, and I sold my 450.

[John Park]

It's done about 500 miles now, and all is well. The motor seems much happier now that I put a .125" [ 3.2 mm] aluminum spacer under the cam chain tensioner, or CCT in acronymics. That put the spring in its normal degree of squeeze and the whirriness went away. This is a mandatory mod if you do the swap IMO.

If you do this mod you will also need to raise the needles a notch, which is also the last notch. The 400s ran on the lean side - one of the benefits of the twin swirl is its ability to operate on leaner mixtures - but it's just too lean for the two valve. It will run, but both you and it will be happier and probably get just as good or better fuel economy with the needles up. Without it the part throttle 4000 rpm running tended to surge and hunt. The 117.5 stock main jets are one richer than a 450's 115s, but probably just as well considering what they cut the gas with these days.

The pilot screws end up at 1 1/4 out, probably because it should have the 450's 45 pilot jets instead of the stock 400's 42.5s. Easy enough to change if it matters to you, but not necessary. And it runs fine on Canadian pump 91 and probably even lesser grades.

By the way, the motor seems to vibrate less with the mixture corrected. A good sign always. Not that these things vibrate much anyway.