R100 engine on a R65???

[fbenach]

Hello everyone.... another question for the wizards!!!

A friend of mine is putting together a "cafe racer style" R65... the original bike is a R100 with its engine working properly...

Now, my friend doesnt want such a big engine on his bike, so we were wondering if we could exchange engines (I dont mind the upgrade), but are not sure if the R100 will fix in my bike and viceversa... anyone tried this? is there any kit/change/thing that has to be done in order to do so?
Will my transmission resist?

Thank you in advance!!!
Regards,
Fernando

[JPSpen]

If he want's an R65 and you want an R100, Then, Sounds like you need to just swap bikes....

And, bike for bike, They're both going to have about the same amount of power.... It's not like the R100 is light years faster than the R65....
A little, Yes, but not as much as you'd think.. Swap bikes and go for a ride and let me know what you think...They'll both scare the piss out of you above 80 MPH...

John

[Julio A.]

Putting an R100 Engine on a lower R65 frame would give engine clearance problems especially during cornering.

I remember seeing an LS model being fitted with a R100 engine, although he retained the R65 gearbox. I forgot who made it, But I am pretty sure it's in the forum somewhere.

Just forget the engine swap thing, It's really just easier to swap the bikes themselves as the frames, gear ratios and a whole lot more are different.

[tvrla]

The frame geometries are the same, though some of the brackets and attachement points are different.

The engines will swap one to the other, and the transmissions will also swap, if they're from the same generation - pre or post 81.

But as has been said, it's probably best just to swap bikes. You'd also have to swap final drives if you swap engines. Then the speedometers would be off, but they won't interchange...

[steve hawkins]

There is only about 1/2" difference in ground clearance between an R65 and a R100.

I have both an R65 and a R100 - the length of the front forks is very similar, if not the same, when the bikes are at rest on their side stands.  The R100 has a longer travel and was more softly sprung as standard than the R65.  

The difference is accounted for in the front wheel size and the rear shock length.  The R100 having a 19 inch front wheel instead of the R65 18 inch.  That is it.  This difference can be tuned out to some degree without major expense (spacer in the forks and shock preload) - if it is required at all.  In the real world you might even be able to scrape an R100 head in an R100 chassis before you scrape a R100 head in an R65 chassis......

I will get my tape measure out tonight - if Justin does not beat me to it.  And put up the differences in my bikes.  However - many people have changed to progressive/firmer springs in their forks and uprated shocks, which will change things.

I feel that this is nothing to be concerned about on a road bike.

If you are cranked over enough to scrape your heads on an R100 then I would suggest you get off the road and onto the track before you kill yourself!

The real difference between an R100 and an R65 is the forks and yokes.  The frames are very similar.  The R100 has yokes with a smaller offset and the axle is mounted in front of the fork leg.  The R65 has a yoke with a larger offset and the axle is mounted in the centre of the fork leg.  This means that the R65 has a steeper steering geometry which makes it steer quicker than the more lazily raked R100.  There might also be a difference in the swing arm length.  this also gives a R65 a shorter wheel base.

Most larger airhead riders would never admit that the R65 has the better chassis than that found in the larger brothers.  And they will come up with all sorts of bollocks to back up their theory.  And the scraping of R80/100 heads in a R65 frame is one such example of internet myth.  They do not understand that the R65 was developed with more sportier credentials that the larger touring bikes.  They cannot get thier heads around the notion that the larger, more expensive, bike does not necessarily make the sportier bike.

Let your mate make his mind up and rejoice in you new found grunt if it goes your way.  

For me I am happy with the R65 engine I have in my Cafe Racer.  and am also happy with the touring R100.  I can afford to have both bikes.  But if there ever came a time when I had to down size to just one bike - then it would be a hybrid.......I.e. I would be putting the drive train of the R100 into my R65 chassis.

Rev. Light

[Julio A.]

So in other words, Putting the R100 Engine and tranny into an R65 is a straight forward and modification free process which would create a bike with the sportier feel of the R65 with the improved power output of the R100 without sacrificing any mobility brought about by the 1/2'' lower ground clearance.

Sounds like the ultimate Airhead to me.

[steve hawkins]

It is.

Its been done many times before, and is certainly easier than trying to pry some more BHP from and R65 motor.  

The biggest worry is the old pre/post 81 business, i.e. the type of flywheel.  You do not need to swap the gearbox, as they are the same unit, if both bikes are from the same era.  But you will need the final drive to match, along with the exhaust (which might have to be modified), carbs, etc.

I do know who will be getting the better deal out of this engine swap though.

[nhmaf]

IF you do not swap the final drive unit and keep the R100 engine with the R65 final drive, the torque of the R100 will give you some faily impressive acceleration off the line, but the engine itself doesn't rev up as quickly, and your top speed will be limited as the R100 engine does have a lower "red line" than the R65.   In most R100 bikes properly tuned up, the R100 will just pull to the redline in top gear, but that is ~ 20MPH more than the R65 top speed.   With an R65 final drive, the R100 will run out of RPMs before it runs out of HP.

[tvrla]

The R100 cylinders stick out an inch farther, and with the ground clearance less on the R65 you could get into trouble on a tight bumpy corner. I've never sraped a valve cover, but know people who have.

When doing the swap, one thing as yet not mentioned is the exhaust. The muffler mounts are different, so custom hangars or exhaust would be in the program.

[wirewrkr]

the exhaust is a pain in the ass,
The rear mounts are only a direct bolt up for the odd shaped R65 mufflers.
Been there done that.

[steve hawkins]

The point I was trying to make earlier is that the R100, as standard, has softer, longer travel, suspension than the R65.  It is after all a touring bike.  The fork length of both bikes, at rest, is the same or very similar - at least my bikes are.  The R100 forks have the ability to travel further from that start point than the R65's can?  

This might mean that an R100 could deck its cylinders before an R65 fitted with an R100 engine when under load.  So if someone was able to deck the cylinders on an R100, it does not necessarily follow that they will deck them sooner in an R65 chassis.

In the end you have to make you decision based on the roads you will be using the bike on and you riding style.  In the UK our roads tend to be flatter - i.e. no excessive camber (although it is present, obviously) and they are not in unreasonable condition.  And we have corners.

I measured some key aspects of my bikes last night and stand by my comments above:

1.  At rest both sets of front forks are the same length.  However I am aware that both bikes have heavy duty springs in them  - i.e. neither are standard.

2.  The rear shock on the R100 is half an inch longer that the rear shocks on the R65.  Both bikes are equiped with Koni's.  However this can vary when you start mucking around with the preload.

3.  The standard front wheel on a R100 is an inch larger in diameter than the R65.  This accounts for the 1/2 inch higher at the front of the R100.

4.  The R100 swing arm is significantly longer than that on the R65.  Which obviously makes the R100 longer wheel base when added to the difference with the forks.  This make the R65 much livelier - which is my experience.

Some things are just a little bit more complicated, when you start looking into them.  Whatever, there is no reason why you cannot easily and cheaply, give the R65 a little longers legs if you want to.

[tvrla]

Interesting data Steve. I'll have to measure the height to the valve covers or the ground clearance. That's not the same, is it?

I believe I weighed my LS and came up with 425 lbs. That could make a little difference in the comparison as well - at the very least, 50lbs lighter than the bigger beemers.

[fbenach]

Thank you all... I get the picture quite clear...

I was expecting more difference on horse power from one engine to the other.... if thats not the case, We will just put together the R100 away from my R65 and have fun driving both!!!

Thanks for the info, you guys are great!!

[tvrla]

You're welcome!

There is a difference in horsepower - but coupled with the lower final drive the R65 doesn't feel that much less. At least for solo riding. Loaded down touring, or with a passenger, you'll definitely notice the difference climbing mountain passes! Count on it!

[wirewrkr]

1.  At rest both sets of front forks are the same length.  However I am aware that both bikes have heavy duty springs in them  - i.e. neither are standard.

I have to disagree, as the forks are an inch shorter on the twin shock R65 bikes, than say on a 79 R100.
At rest is not a good way to compare apples and oranges for these factors. same goes for the shocks.