Project X

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astrax
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Re: Project X

Post by astrax »

Alan H wrote:I hope you didn't turn down my fork brace to make those Ian. :?
And those holes in the bra things will never get a fork leg through them........
Did Madonna's bustier maker do the cad drawings btw? :shock:
Hi Alan
Yes it does look like something she would have worn, probably a bit cold and heavy, but thanks for the idea, I could see how they do on eBay in the Madonna's merchandise section. :lol:

I'll see what I can do about the fork brace in the few days I have off

Ian
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astrax
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Re: Project X

Post by astrax »

madforitkev wrote:Ian

Looks the dogs mate. Be interested to see how the head machining goes. Might need to drop round for a brew sometime for a chat if you are up for it.

Have you got the case profile as a DXF?
Kev
Yes I have the casing image as a DXF :D
Used it for gaskets and also made blank plate for the casing for when blasting or painting.

Yes welcome to come round for a cuppa.
IMAG8199.jpg
IMAG8202.jpg
madforitkev
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Re: Project X

Post by madforitkev »

So I've started on the squish head.

I started with mapping a design for the standard kettle (70mm bore) first, which has a 0.5 clearance at TDC and a 30ml head volume.

So allowing for an average squish band % of 35 and a velocity of about 20ms and an additional head clearance of 0.5mm, it works out to be;
std750head2.jpg
My special has a 70.5 bore with a zero deck height so I have made the squish clearance 1.0mm to compensate (plus gasket but i might change that later). Also the compression ratio will now change because of the zero deck and bigger bore but for now I am going to ignore that as the plan is to make replaceable squish skull caps and adjust on the dyno as I go.

So the modified design head is;
plus05head2.jpg
Ian and I are chatting about developing the skull caps and modifying standard heads. All good fun :D
Honest baby....this is probably the cheapest bike I have ever bought!!
teazer
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Re: Project X

Post by teazer »

Check the thickness of a stock head. You will probably have to flatten that insert/dome a fair bit to get it to fit inside the head shell.
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astrax
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Re: Project X

Post by astrax »

teazer wrote:Check the thickness of a stock head. You will probably have to flatten that insert/dome a fair bit to get it to fit inside the head shell.
Hi Richard
Kev is doing a new version as the dome would have protruded out the top of the head.

We need to keep it below 25mm including 9 - 10mm wall thickness or the insert will become air cooled ;)
teazer
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Re: Project X

Post by teazer »

Another issue to keep in mind is that where the stock "dome" meets the top skin of the head, there is not a lot of metal to seal an O ring.

I bought a head with inserts and didn't like what I saw, so I had a head sectioned across all plugs and it's not as stiff as we might like but can be made to work.

In terms of shape, think wide and flat top to keep it low and leave the old hemi shapes behind. Bring the plug down further into the center of the burn, so to speak. And contrary to everything we have been told about gas flow and combustion, Sharp changes in section are not always your enemy. :o :)
madforitkev
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Re: Project X

Post by madforitkev »

Having read the threads on the forum about the GS gearbox conversion for the GT, I decided to try to summarise them all in order to do the upgrade for the project bike. Hope I’ve got this all right!!
As the thread highlights, the reason for doing this is to primarily take advantage of the better ratios of 1st and 2nd on the GS. You also get a modern output shaft sprocket fitting to allow for a larger range of sprockets.
Bit of ebaying turned up a GS750 (1980) gearbox. Although digging through specs, there is some confusion where the GS’s ended and the GSXr’s took over.
Anyway, the ratios for the GT’s, GS and GSXr ratios seem to be similar;

750 A \ GS \ GSX E
1 – 2.84 \ 2.57 \ 2.5
2 – 1.83 \ 1.83 \ 1.75
3 – 1.38 \ 1.38 \ 1.37
4 – 1.13 \ 1.3 \ 1.13
5 - .96 \ .96 \ .96

So there isn’t much between the GS and the GSX, so I’m happy I’ve got the right box without counting all the teeth!
The forumed basic changes are;
Input shaft (clutch) is the same width between bearings as the GT so it drops right in. The GS shaft is longer which means mods to the clutch basket (6mm counter-bore) to make it sit back in the same position on the splines as the GT and remove 6mm off the length of the shaft (clutch side) to stop it clashing the outer case and having done that (and ending up with a shorter thread for the nut), undercutting the thread to allow the nut to go all the way on again.
The GT lubricates the input shaft gears/dogs by passing oil down the shaft through a central hole that is fed by the primary gear (clutch) picking up oil and dropping it into catch trays that then feed it to the end of the shaft via an oil seal in the shaft. This seal is missing in the GS and the shaft blocked so the GT feature has to be replicated in the GS shaft.
IMG_1710.JPG
Seal shown on output shaft of GT with none on the GS.

I am fitting a dry clutch so I have other issues with lubrication (later).
The output (sprocket) shaft on the GS is 1.6mm longer between the bearings. The easy way to fix this appears to be;
1. Fit the right hand (bike clutch side) bearing of the output shaft in its correct place with the ½ moon retaining clip in place. This allows first gear to rotate without clashing on the case.
2. Now it is easy to see that the right hand bearing (sprocket) is 1.6mm away from the retaining clip groove line-up.
3. Take the sprocket side bearing off and machine 1.6mm of the inner race (bit that touches the shaft). This is easier that machining 1.6mm off the hardened shaft bearing face, which would move the bearing in as well.
4. The output shaft also needs the oil seal fitting in the end opposite the sprocket as in the input shaft mod.
Next, the GT’s output shaft has a larger oil feed hole in the bike clutch side of the shaft. The excellent U tube video on this conversion suggests opening up the GS hole to match the GT as the GS end bearing suffers with a small hole.
My output shaft doesn’t seem to have that hole at all (see questions at end), although there is one under first gear. I assume it because my output shaft has a bearing rather than a lubricated sleeve.

The GT also has an oil feed hole in the input shaft that feeds the clutch basket roller bearing carrier. I cant see any references to modifying this on the GS shaft and my GS shaft has a smaller hole in a different position (within the splines) that doesn’t seem to be under the roller bearing carrier position I am unsure how the GS shaft oils the basket roller bearing carrier?
IMG_1709.JPG
GS shaft on left showing small hole NOT in-line with GT bearing carrier oil hole position on the right shaft (end bearing removed).

The last noted modification I can find is that when all mods are done and the cases trial assembled, one of the gears (probably first, haven’t checked yet) snags on the oil catch plate in the upper casing. So if the gears won’t spin, check that!

KNOWN MODIFICATIONS SUMMARY
1. Fit oil seal recess to both GS shafts (bike clutch side)
2. Shorten input shaft clutch side by 6mm and undercut screw thread
3. Machine 1.6mm off inside bearing sleeve on sprocket side of output shaft.
4. Open up oil feed hole in output shaft (clutch side) to match GT

Questions.
1. My GS output shaft does not have the shaft lube hole at the bike clutch side under the bearing. How can oil get into the shaft and gears/dogs? Is it really a GSX shaft and if so how does it lubricate? Are the holes (picking up oil in the gearbox along the shaft) enough without an end feed?
2. Do I need to change the input shaft clutch basket bearing carrier oil feed hole? It doesn’t line up with the bearing position will be on the GS shaft.
3. I am tuning to around 100bhp and am concerned about the side loads on the bevel primaries. Should I move to straight primaries?
4. Because of the dry clutch complications, I am going to have to feed lubrication for the clutch shaft from the left hand engine side (rear sprocket). The output shaft can still get its oil using the catch plate system for that shaft in the GT because it is still in the ‘wet’ bit of a dry clutch. I cant see why the input shaft lubrication cant happen naturally as the gears spin because there are oil holes in the shaft anyway but I suppose oil needs to move along it which is why the GT shaft fed the oil in from the engine clutch side to the shaft holes? Not sure how to fix this yet in a dry clutch?
5. Finally, I’ve seen some comments about dogs clashing with this (or the GSX) mod, but I can’t see any evidence yet. Anyone had any experience?
Last edited by madforitkev on Sun Jan 07, 2018 9:11 am, edited 2 times in total.
Honest baby....this is probably the cheapest bike I have ever bought!!
madforitkev
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Re: Project X

Post by madforitkev »

On a more detailed inspection of the GT shafts and dogs, there are no oil feed holes visible like there are on the GS. So my conclusion is the GS lubes its shaft/gears/dogs via these holes whereas the GT needs the end shaft oil feeds.

So I assume the GS relied on the oil pump to feed these shafts rather than just pickup from the gears?

So how did the GS pump feed these holes/shafts? More digging......
Honest baby....this is probably the cheapest bike I have ever bought!!
teazer
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Re: Project X

Post by teazer »

All I did was to cut a groove in the GS/GSX shaft to get oil to the clutch needle roller bearing.

I had the shafts machined to take stock GT oil feed bearings, but you also have to block off the open (sprocket) end of the clutch shaft. I am not hear my bikes or records, but I think the GS/GSX used a push rod and an oil seal around that, where a GT has a puller arrangement and no traditional cross bike push rod.

With a GS shaft, the shaft has a shoulder that can be machined down but bearings do have to be machined.

You might be surprised how many bikes including old TZs that use GT or GS type splines. GT shares splines with RD350 and H2 IIRC and GS and GSXR are the same.

Gears don't clash as long as the shafts are set up correctly and the 1.5mm comes off the appropriate sides of both shafts. Gears do rub on some/most cases and require a touch of clearancing. They also foul the oil catch tray in the roof of the upper crankcase half. A Dremmel will fix that as it's a tiny amount that has to be removed.

Don't forget that GS series have a lower top gear which is closer to 4th. Nice on the road but it does drop top gear speed. I was in a rush last seasoon to replace the trans with a GS and forgot that minor change and that cost me 3mph at the deep end.
madforitkev
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Re: Project X

Post by madforitkev »

Thanks.

So looking at it more, I am not worried about oiling the shafts/dogs/gears as once she spins up, oil ends up everywhere anyway and again the GS shaft has lots of nice big oil feed hoses through the dogs.

The input shaft (sprocket side) bearing with the blank cap needs to be lubricated properly and some race TR designs have made an oil way to the gap between the blank cap and the outer bearing face by modifying the top casing splash plate and feeding oil through new oil way holes in the casing. Then again some don't bother so I will decide later. The clutch side of the input shaft is in the wet zone anyway and get lots of oil thrown around by the primary so that should be OK.

So it looks like the GT only fed oil down the middle of the gear shafts to lubricate the dogs and the GS copes with that with just more and bigger holes rather than a central feed.

On the output shaft though I will keep the GT central feed just cos its there and in the wet section of my dry clutch. Combined with the bigger shaft holes it can only improve things.

I need the central feed hole of the input shaft anyway for my hydraulic clutch adaption (pushrod) so that will need an oil seal at the clutch end.

When the RS clutch comes in next week I will work out how to lube the bearing. Dryclutch casing should also be in next week :D
Honest baby....this is probably the cheapest bike I have ever bought!!
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