'74 R90S crankshaft in R60/5 engine case ?

[StephenB]

Ken in B.C. has the engine case that matches my frame (that I got from him years ago) and I have decided to make my non-matching R75/5 a matching-numbers R60/5 with an engine upgrade either to 750cc, 800cc or maybe even 900cc. As a positive side effect I might learn a thing or two about installing a crankshaft, one of the deeper secrets of the Airheads that I haven't mastered yet. I am heavily relying on gspd to help me with that but don't tell him he doesn't know yet!

Now, Ken B.C. also has a believed-to-be 1974 R90S crankshaft that I could buy of him. I have asked for part numbers or is there any other way to know if it i9ndeed a 90S crankshaft? Now, that may or may not fit the crankcase. Anybody any first hand experience? Are there different versions of this crankshaft? What about running stock 750 or 800cc (1986-on) heads with that type of crankshaft? Or 750cc heads with 800 or 900cc barrels? Any negative effects or clear NoNos?

This isn't for a race bike application but for a daily runner that I intend to keep for the next 25-30yrs.

Any info would help. It's not a short term project but start could be as early as this winter.

Stephen

[gspd]

Stephen, Stephen, Stephen -

I don't think you'll need much help on this, it very simple.

There are only 2 different type 247 (stock) cranks,
the old ones had 10mm flywheel bolts, the later ones are 11mm.
I think the changeover was in 76.
they are interchangeable if you change the flywheel in accordance.

If you try to measure a used crankshaft journal precisely (and I know you will), you'll go nuts;
it's like trying to measure the roundness of an egg.
Crank journals never wear uniformly around their circumference.

All the con rod bearings are the same size, and only one size is available.*

I think there are now only 2 sizes ( used to be 3?) of main bearings available.*
For the main bearings, order one of each and test fit them to determine by feel which is a better fit.
Use the one that has the least play as long as it fits on and turns freely.
They get slightly tighter once pressed in to their housing.

If the crank has more than xxxx miles, it will be way out of spec, but still perfectly good.
EDIT: If it's smooth, no lines, scoring or blueing.

* There are +.25 +.50 and .75 oversize main and rod bearings if you need to regrind the crank.
I know of nobody in North America that does this properly (as good as OE).

[Max Headroom]

FWIW, Motobins still supply four grades of main bearing shell, to allow for variations of journal size. The factory manual has the grades listed along with the matching shaft sizes. As GSPD has mentioned, the cranks are all interchangeable apart from the flywheel bolt change. My inner pedant wants to correct GSPD's date of the bolt change to 1975 though, not 1976 . . .

Every reground crank I've encountered has subsequently snapped, so using a good second-hand crank is preferable to a reground one IMHO, should you ever find yourself in that position.

As for performing the crank swap, the work is straightforward enough if you have access to some resources. You'll need to rig up a device for removing the front bearing assembly, but that's simple enough if you use some 8mm allthread and a short length of angle-iron. Removing and installing the main bearing shells will require a bush machined out of steel or similar, and some heat (no, not a Magnum or .303, the OTHER kind). Removing the old front main bearing shell and refitting the new front main bearing shell will require an awareness of the little locking pin as well as the need to drill the oil holes for the rocker feed, but we can explain that in more detail when you get that far.

You'll find it helpful to have access to a DTI for checking the crank endfloat, micrometers and dial gauge, and the 10mm double-hex adapter for the big-end bolts. And some heat (no, the OTHER kind).

[StephenB]

There are only 2 different type 247 (stock) cranks, the old ones had 10mm flywheel bolts, the later ones are 11mm.

So, all engines up to 1975 or 76 (500, 600, 750, 900) had the same cranks and presumably same camshafts as well?

If you try to measure a used crankshaft journal precisely (and I know you will) ...

Will take your advise and will not.

All the con rod bearings are the same size, and only one size is available.*

I think I knew that.

I think there are now only 2 sizes ( used to be 3?) of main bearings available.*
For the main bearings, order one of each and test fit them to determine by feel which is a better fit.
Use the one that has the least play as long as it fits on and turns freely.
They get slightly tighter once pressed in to their housing.

So, here's where experience makes the difference between a successful swap and a knock after the first 250mls (you know now why I need your help!).

If the crank has more than xxxx miles, it will be way out of spec, but still perfectly good.
EDIT: If it's smooth, no lines, scoring or blueing.

I can visually inspect and make a determination ... is what you're saying.

As for performing the crank swap, the work is straightforward enough if you have access to some resources. You'll need to rig up a device for removing the front bearing assembly, but that's simple enough if you use some 8mm allthread and a short length of angle-iron. Removing and installing the main bearing shells will require a bush machined out of steel or similar, and some heat (no, not a Magnum or .303, the OTHER kind). Removing the old front main bearing shell and refitting the new front main bearing shell will require an awareness of the little locking pin as well as the need to drill the oil holes for the rocker feed, but we can explain that in more detail when you get that far.

You'll find it helpful to have access to a DTI for checking the crank endfloat, micrometers and dial gauge, and the 10mm double-hex adapter for the big-end bolts. And some heat (no, the OTHER kind).

Check, check, check, check, check and check, check.
I think installing the main bearings gives me the biggest scare but then its all about heating one part and cooling the other. What is it, a tight pressfit or something? Locking pin, that is "the other $2000 item" apart from the white $200 O-ring on the later Airheads, right? Prevents some kind of rotation of the bearing shell, doesn't it? Have to read up on that one again.

So, about running 900cc heads or the latter 800cc heads and barrels: running up to 75/76 900cc barrels, pistons and heads shouldn't be a problem then in the /5 crankcase. The latter 800cc will have the issue of the barrels not fitting without a bit of machining, which isn't a big deal either. But their (power) advantage over the 750cc is not worth the effort to making them fit I would think. 900cc would be nice but are hard to come buy and maybe the front drum brake is not really up for that job. Although, it's only ten horses and 10-15mph on the top speed ... maybe I should stick to 750cc.

I will start a thread describing this work for documentation and max. feedback from the community.

Thanks for now, gspd and Max.

All good, Stephen

[Kurt in S.A.]

AFAIK, the R60/5/6/7 had a more agressive cam profile, so the camshafts would be different.

Kurt in S.A.

[gspd]

SB asked:"So, all engines up to 1975 or 76 (500, 600, 750, 900) had the same cranks and presumably same camshafts as well?"

There were a few different factory cams, and tons of aftermarket cams; they will all work, but they provide different power and torque curves

I can visually inspect and make a determination ... is what you're saying. So, here's where experience makes the difference between a successful swap and a knock after the first 250mls (you know now why I need your help!).
The journals have to look perfectly smooth and polished. If you see (or feel) lines or gouges on the journals,
there is a good chance it won't last almost forever. But it still might.
Once the crank is installed, it must spin smoothly and freely in the case on its new bearings. If you feel any uneveness when turning it by hand, it probably won't last. The crank should have no detectable (by feel) front to rear play (end play).

So, about running 900cc heads or the latter 800cc heads and barrels: running up to 75/76 900cc barrels, pistons and heads shouldn't be a problem then in the /5 crankcase. The latter 800cc will have the issue of the barrels not fitting without a bit of machining, which isn't a big deal either. But their (power) advantage over the 750cc is not worth the effort to making them fit I would think. 900cc would be nice but are hard to come buy and maybe the front drum brake is not really up for that job. Although, it's only ten horses and 10-15mph on the top speed ... maybe I should stick to 750cc.

If you stick to a top end (pistons, valves, heads and barrels) that originally came together it will work.
If you mix and match, it''s an experiment, unless you know someone who's done the exact same swap and successfully ridden it for many miles. A 10 HP variance is HUGE on a airhead. Not just for top speed, but for torque (passing power).
Some barrels won't fit some cases and machining will be required.

[Lasse]

I am having abit of the same "issue" Running an R60/6 which I at some point would like to beef up to a 900cc.

Would the R60 cam work good on a 900 kit?

[gspd]

They all work 'good'.
There is always a compromise with any cam selection.
No cam made can increase low end AND high end power simultaneously.
As a general rule, more lift and duration increases high rpm power, but this is at the expense of low end tractability and smooth idle.
That's why a lot of performance engines have variable ratio cams and variable cam timing, (V-tech Honda, etc)

The best way to increase airhead power across the board is by increasing engine displacement.
There is simply no substitute for cubic inches.

[Lasse]

Sounds good, if I can just get the power between 2500 and 5000 RPM I am good

Do you know if I have to change my exhaust system?

[gspd]

Not if it's in good condition. The stock exhaust will work fine for that rpm range.
A free-flow exhaust will increase power at higher rpm (over 5000) but can actually decrease power at low rpm.