Crankshaft Rear Oil Seal

kettle738 · Jul 27, 2018

My recently acquired 1981 R100 was impressively oily....on the outside, and had signs of a long standing crank rear oil seal leak.

The engine is out, clutch and flywheel removed and to be honest I think the culprit is just as likely to be the oil pump O ring...(which I will look at next)....but having come this far, bought a new type oil seal and spent a morning turning up a tool to fit it I want to finish the job.

I have got as far as you see in the photo.......if it works ..... but the crankshaft end boss is very firmly in place and I'm extremely reluctant to use any force for fear of damaging something. Looking at it.....I would guess at some sort of clamp around the part that sticks out at the centre and a decent slide hammer.

I guess I could fit the seal around the crank end boss, but I'd rather use the tool I went to some trouble to make.....any constructive advice to remove the end boss without damaging anything......or a method that avoids removing it would be much appreciated.

Mick.

KSAS · Jul 27, 2018

The end cap o-ring groove can get chocka bloc with cruddy crud...
a bit of heat and a smart tap at a 45 degree angle to the inner edge of the flywheel bolt drilling using a 1/4 extension bar as a drift should rotate the end cap so the drillings no longer line up. This should break up the crud.. from there you can lightly pry between the drillings of the end cap and the crank and it should start moving.

Done this on many and caused no damage.

It's definitely worth removing the end cap as you'll want to change the inner o-ring and clean the groove.

mikeyboy · Jul 27, 2018

Support the crank so it cannot move forward,if the inner crank thrust bearing drops out you will be cursing

kettle738 · Jul 28, 2018

Thank you for the advice all appreciated and taken on board......since when I've had a success and a minor disaster; I was a bit wary of hitting the crank boss with anything...simply because it's a new job to me and until it's off and in my hand I don't fully appreciate the mechanics of it, so I played safe and made up an adapter for a slide hammer to pull it off.

With the boss suitably warmed up with a hot air gun it came off first strike of the slide hammer.....that was the success; getting the new seal in also worked like a charm with the installation tool, aided by the fairly pronounced chamfer on the seal housing.

The cock up was a stupid and simple mistake, I drilled three holes in the old seal to screw in self tappers to pull it out....and it worked perfectly.......but with hindsight I wouldn't have done that, I would have pulled the crank boss off first and prised the seal out with a seal puller.

In the event, the last hole I drilled (over confidence) I made a momentary slip and put a scratch in the seal face of the crank boss; :blast

worse still, the crank boss had been in really nice condition.....I have polished the scratch with 1200 grade wet and dry and to the naked eye it's barely visible....the photo really shows it for what it is....but I can feel it with a fingernail, so I think I'm in line for replacing it

The scratch is just forward of the polished ring on the crank boss left by the old seal, but of course I don't know where the new seal will bear on it, so I guess I have to play safe and renew it....I'm more than a bit annoyed at myself, but hopefully I'll learn from it.....
Mick.

solidstate100 · Jul 28, 2018

How annoying! But you are right, best replace it, even more annoying to re-assemble and have it leak and have to yank it all out again.

Reminds me when I did a fork rebuild years ago when i was young and stupid and overconfident - did a fork strip and rebuild with new stanchions, went to put the fork seal in one of them (without the correct tools of course) and first tap on the seal managed to out a nice large dint in the brand new stanchion. Flatted/polished it out as best as I could but it still chewed the seal and leaked. After about 5 new seals I had to accept the inevitable and buy it all over again.....

mikeyboy · Jul 28, 2018

I’ve probably got one of those knocking about.
I can have a look on Monday if you can wait,
Down side is,you may need to adjust the crank end float,
Do you have the barrels off?

kettle738 · Jul 28, 2018

Thank you for that........but I have already ordered one from Motobins........why the need to adjust crank end float if I am simply swapping like for like?....the only wearing part is the surface touched by the oil seal......adjusting crank end float sounds like something I definitely don't want to get into if I don't have to

.

Mick.

mikeyboy · Jul 28, 2018

kettle738 said:
Thank you for that........but I have already ordered one from Motobins........why the need to adjust crank end float if I am simply swapping like for like?....the only wearing part is the surface touched by the oil seal......adjusting crank end float sounds like something I definitely don't want to get into if I don't have to.

Mick.

Not so mick,
The crank end ring is the other surface that controls float,hence the other thrust shim behind the oil seal.
You’ll have no idea if it’s the same thickness as the old one if you just fit it!
Chances are it’ll be fine but you need to know for sure or you could sieze it.

mikeyboy · Jul 28, 2018

If the barrels are off it’s dead easy to check,
Bit trickier if the rest of the engine is built

kettle738 · Jul 29, 2018

Oh Crap!......just what I didn't want to hear, but I do appreciate you telling me nonetheless :thumb2

.

Can I measure the new part against the old?......are they not at least nominally all the same size?

I have micrometers, and a dial gauge, but I've always been poor at reading/using them so I tend to limit myself to tasks that are suitable for a digital vernier gauge, avoiding anything that requires more accuracy than that, but apart from the usual impatience to crack on, I'm not in any huge rush so I'll learn if I need to...or buy a digital set..or both.

I take it the critical measurement (compared to the old part) is the depth of the internal recess of the crank boss?

I will be taking the cylinders off to replace the very manky pushrod tubes, but the plan is/was to refit the clutch, put the engine back in the frame and then remove the cylinders once the engine is securely mounted......perhaps I should think about making a simple engine stand and do the whole task on the bench...

I take the point about it being simple to check with the cylinders off (no idea why that should be or how that's done as yet) but how easy or difficult is it to adjust if required? ........ presumably the clearance can only be checked by fitting the new part? .....would nipping up the flywheel just tight enough, using an old set of bolts be sufficient to check the clearance? '

Twenty years ago I would have approached this with a 'can do' attitude and enjoyed the challenge.......but nowadays (one of the joys of getting older I guess :rob

) I'm my own worst enemy, over cautious and paranoid about damaging something (slipping with a drill for instance :blast

) and I really don't like getting out of my comfort zone......but on the other hand if I can stop myself worrying about cocking it up I might just learn something......

Mick.

mikeyboy · Jul 29, 2018

Crikey where to start,
If you take the sump off ,the engine sits flat so no stand needed.
I’d take the cylinders off now then refit them once the motor is back in the bike as it’s loads easier just to drop the crankcase in.
The critical measure ment is exactly as you say.
However you don’t know how worn the thrust bearings are so worth checking anyway.
It is really easy to measure through the RH side of the crankcase,once the end cap is refitted (without the seal),assuming the crank rotates ok once the cap is tight.
Simply push the crank forward and check the gap between the the crank and the inner thrust bearing,with feeler guages
If the clearance is incorrect it can be corrected by just swapping the outer thrust bearing for one the correct size.
Hope this makes sense.

kettle738 · Jul 29, 2018

Thank you again Mikey.......typically I have just refitted the sump with a new gasket and of course, also fitted the new crank rear oil seal, which went in so very nicely....will that make measurements from the right side of the crankcase impossible?

The new crank boss should arrive by Tuesday at the latest, I'll measure it very carefully against the old one and see what's what.

By a stroke of good fortune, this morning I found a retired diesel engine mechanic local enough to me, selling a couple of Mitutoyo dial gauges along with a metric/Imperial Digimatic Indicator, a magnetic base gauge holder and a Noga arm with a large clamp.....and all for a pittance.... so one way or another I should be able to hold a decent gauge completely steady to get an accurate comparison.....

I think I understand what you are telling me about measuring end float through the right cylinder aperture, and I'm sure I will understand once I'm looking at it. If I'd known what I know now, before I started, I would have done the job in a different order and not damaged the crank boss...but that's life...

Your advice is very much appreciated, measurements to follow soon.

Mick.

mikeyboy · Jul 29, 2018

You can of course measure the end float with a dti.
But if it’s outside of tolerance you’ll have to pull the new seal out to retrieve the thrust washer for measuring.

kettle738 · Jul 29, 2018

Understood........I guess I'll have to cross that bridge when (if) I come to it.....at the moment, fingers crossed the new part is either identical to the old one or so little different as to be insignificant.

I take it the thrust washers would pull out with a small telescopic magnet?

Mick.

mikeyboy · Jul 29, 2018

They can be a bit tight on the two dowels,
I normally get a small pick behind it and gently lever it off

kettle738 · Aug 1, 2018

My new crank boss turned up from Motobins today which gave me an opportunity to try my new digital gauge....the hardest part was re setting the gauge to zero each time, even though it was very firmly held, the ham fisted touch of fat fingers to re set it often produced a tiny error.

Repeated tests showed new crank boss had a 'cup' depth of 11.01mm; turning the boss on my attempt at surface blocks with the pointer on the rim showed it to be flat.....the old boss had a cup depth of 11.06mm and it varied between 11.08 down to 11.04.....but I think the variation was down to a tiny amount of corrosion it has on the exposed face.

Subject to advice to the contrary, at 0.05 mm difference I feel happy to temporarily bolt up the new boss to 30lbft or so using the old bolts so that I can turn the engine, hopefully check the end float and remove the left cylinder.

I have the right cylinder removed but I'm not totally sure where end float would be checked...the crank seal is in situ... I can see in the photo what looks like the thrust washer and one of the pins it sits on....I take it the clearance would be between the thrust washer and the crank boss once it's bolted up?....as shown, the crank is blocked....pushed rearwards.

I watched someone on another site checking by setting up a dial gauge at the flywheel then hitting the rotor bolt with a rubber hammer, or push/pulling the flywheel by the bolted on locking tool....I've made a crude engine stand which will allow me to hold it steady so that method I could probably manage if my gauge has a facility to 'retain' a peak reading.

Mick.

mikeyboy · Aug 1, 2018

That’s it,by rotating the crank you will find the spot that gives you the most room to work,
With the boss tightened up ,push the crank forward and check with feelers

kettle738 · Aug 1, 2018

Got that, thank you.....now I'm getting my head round it, it looks less intimidating than it did at first........I suspect I might have got away with the scratch on the original crank boss as it was outside the area swept by the old oil seal.....but I guess the new one could have a different contact point and I don't feel like doing it twice.

Thank you for the valuable advice, in my ignorance I would have treated it like a Japanese part and just expected it to fit exactly with no further intervention......all good learning. :thumb2

Mick.

mikeyboy · Aug 1, 2018

Chances are all will be fine,
But worth Knowing all is good rather than just hoping it

kettle738 · Aug 2, 2018

Today's progress involved fitting the new crank boss which was a nice tight fit in the new oil seal, and initially (temporarily) torquing it up to 30lb/ft.

Using the digital gauge set up on the flywheel I found a gross end float...full push to hard pull of 0.14mm, I was moving the crank as forcefully as I could so I'm happy that is the maximum. I couldn't see that movement, nor do I think I would ever have found it with a feeler gauge, but it's within spec so I'm happy enough with that.

A new oil pump O ring was fitted and the left side cylinder removed.....I found a couple of small scuffs on that piston which was a bit of a surprise; the engine seems remarkably clean inside and the opposite piston was unmarked, so no complaints..

Mick.

Crankshaft Rear Oil Seal

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