Pre-unit or Unit

[radical]

Which is the better?. The older bikes had seperate gearboxs which meant they had their own oil and cross contamination didnt happen unlike modern unit constuction bikes, I know there may be unit constucted bikes like the Honda xr range and possibly the Royal Enfields available that have seperate gearbox oil/engine oil but they are far and few between. There are other advantages of non unit construction in that you can change/repair the gearbox or engine without disturbing the other. What are your veiws as regards unit/pre unit construction?

[tatters]

Eaiser to work on the gearbox is the main one, take me 30 mins to remove the one on my BMW. unit construction saves weight and space.
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Past:NRG50,AF1125(x2),NSR125RR,ZZR250,CX500,VFR400,KR1S,ZZR600(x2),CB400N,YZF1000(x2),KH125,Z200,FX400R,CBR954RR(x2)GPZ500S,GT550,VFR750F(x2),RD350N,XR650R,CBR600F,CB250,KDX250,YZF750R,CRM250,400EXC,KLR650,TTR600RE,DR350S,R100GSPD,RGV250,VMAX1200,DL650,KZ750 Present:G650XC,C12,CRF450X,1190ADV

[Blau Zedong]

Pre unit - too bulky and not stiff enough for high performance applications.
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18:54:48 Rob Fzs: jews don't give away stuff for free

18:54:59 Rob Fzs: unless its their clothes/ hair/ golden teeth

[radical]

[r0b]

don't most of the 4-stroke mx bikes have separate oil for the crank and the gearbox ?
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'92 Honda NX650 Dominator RD02
'98 Kawasaki ZX9R C1
'00 Yamaha TT600R Belgarda

[radical]

I understand that the XR Honda range do have seperate oil for engine/gearbox and possibly the older RE bullets which are unit construction My biggest complaint about shared oil is the chances of a gearbox cog getting chipped and steel getting into the oil which could cause massive damage to bare alloy bearing faces and pistons etc which are the norm on modern u.j.m, I beleive that a gearbox will run better on a different grade of oil than a high revving engine will and that modern methods of construction are just cost saving measures but the Xr range of bikes have proved the point by going to seperate gearbox oil and the traditional dry sump lubrication system as opposed to the wet sump system.

[r0b]

All the honda XRs ive seen have the same oil for engine/trans. Sure its a dry sump system -but that just means it has an external oil tank as opposed to keeping oil in the sump. I have an NX650 (similar to XR600 XR650L engine) and Yamaha TT600R (XT600 engine) both are dry sump with the oil shared between engine/trans. The oil is kept in the frame on the honda and in an alloy tank on the yamy

The bikes I know for sure have separate oil for the engine are CR250F and CR450F and I suspect a lot of other hi-tech competition 4-stroke mx and enduro bikes
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'92 Honda NX650 Dominator RD02
'98 Kawasaki ZX9R C1
'00 Yamaha TT600R Belgarda

[radical]

[Ariel Badger]

Pre unit everyday, stripping a box takes a hour rather than a week.
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Bikers make great organ donors, get 115 on your licence today.

[radical]

[Dibble]

[johnsmith222]

It would be great if modern bikes were pre-unit. You hear of plenty bikes with problems with second gear (ZZR600 and R6 are two).

Also, the parts that get damaged are probably really cheap, but the problem is the shit you have to do to fit it.

[Teflon-Mike]

Remind me again how to tension the primary drive chain on a pre-unit Triumph Trophy?

I seem to recall that apart from the small niggle of the mixed bag of imperial, metric and witworth fastners used all over the place....

There were RATHER a lot of bolts that had to be undone, major assemblies slid forwards and backwards in slotted holes in the frame and the primary drive chain case, then the final drive chain re-tensioned, and THEN bolting it all back together so it was even laughably oil tight was err.... something of a pain!

And didn't it give three oul levels to check, becouse the primary drive ran, 'wet'... as long as the oil stayed in there, of course!

From the point of view of engineering asthetics the vertically split, unit construction, with all gear drive arrangement is a LOT more elegant.

The manufacturability is hugely increased; the rigidity of the unit increased, the maintainance requirements minimised, and generally, its just a lot 'neater'.

Yes, the pre-unit construction has some minor advantages, but not many, and they are pretty much limited to 'serviceability', but where and when?

So, it MIGHT be easier to pull out a seperate gear-box to make a repair to a selector fork, IF one is so worn or damaged, but if you had a unit construction engine, how much faffing about adjusting primaries and the like would you have saved before that effort was needed?

As for gear-teeth chipping and damaging components inside the engine?

Yeah. Broken bits of metal inside a motor are not good. But if you have an engine that has been that abused or neglected or just that worn out... I think that there may be bigger issues to worry about, and IF that shard got past both the oil filter and the strainer, to actually do some damage, I think that it would pretty much be a message from Thor, the god of metal work, it was time to strip your engine and give it some tender loving care, and some new bearings!
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