350 crankshaft question

[Jordan]

That's a good summary of details to check, thanks Matt.

[DBDBrian]

As Matt has said a pressed up crank is a pressed up crank, but to be certain not to damage things, a solid jig is important. This is a jig and mandrel's I made to press apart and assemble my 200 crank. I thought it may be of interest.

The pictures are just mocked up, the crank was assembled a while back.
Brian

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TUBE AND SLOTTED PLATE

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CRANK IN JIG WITH SUPPORT PLATE FITTED

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CUSTOM MADE SPACERS TO SUPPORT CRANK
AT WASTED SECTION BESIDE PIN, WITH PRESS
MANDREL IN POSITION

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SUPPORT PLATE AND MANDREL, MACHINED TO
ALLOW IT TO BE ON CENTRE WITH PIN

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CRANK TIMING SIDE PRESSED ONTO PIN
AFTER BEING PRESSED INTO DRIVE SIDE

[Jordan]

Thanks Brian,

Those are interesting photos indeed.
Your jig sure is optimised to the hilt, for one particular crankshaft.

[DBDBrian]

Yes Jordan, it's a belt and braces arrangement for sure, as things are under a lot of pressure before the pin makes it's first move, mostly with a jump.
I usually true cranks on the bearings if possible, as it eliminates any possible errors with running them on the shaft centres.

Brian

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[LaceyDucati]

Hi,
As this has been my bread and butter for the last 20 years I will just add a few comments:

Firstly one main difference between a Ducati Single crank and your average two stroke crank is: If who ever does the job buggers it up, you can't easily get another! Believe me a lot of cranks I get sent are damaged or unserviceable due to previously shoddy work, so it's not that straight forward for some. However using a "specialist doesn't" guarantee a good job and a broad recommendation is king.

When building a crank with a stepped pin I would never shoulder a pin as that will possibly lead to a broken pin (especially in a race bike). Also those side faces where the shims sit are nearly always not straight. Shouldering the pin will more than likely pull the crank out of true if it is pressed hard against these faces. If possible I machine true these faces, but even still I wouldn't shoulder the pin. My rod kits are designed to be stopped about 4 or 5 thou short of the face either end when the correct side clearance is achieved. Most pressed cranks use a straight pin so this will not be an issue many will have faced or even thought about.

Brian your jig looks good and puts my much used jigs to shame. However I have to do a lot of differing cranks and therefore I am a bit more seat of the pants with a multitude of shims, spacers and a lot of checking I would however make two comments, I use a brass pusher for pressing the pin out, as that way there is no chance of catching the hole and any potential damage. Also I would not clock the oil nose on the timing side as there is always off centre wear. A good trick is to put a 6202 bearing on the bevel mount and clock that. The only thing that needs to be checked is, that there is no burr on the edge of the keyway as that can give false readings. Otherwise this is a far more accurate/important place to clock (see pic)

Accuracy- I use "tenths" clocks as that way you can see a thou easily. When clocking on the ends (bevel and cover bearing diameter) while running on the mains, I like to see a runnout of less than 1 thou (0.025mm) (TIR) or ideally perfect When clocking the main bearing journals while running on the ends I work on less than 8 tenths (0.02mm). Unfortunately occasionally you have to compromise.

Regards Nigel

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[double diamond]

Another caution: Flywheels have a countersink on the inside so the flywheel can be turned between centers. Check the countersink on the inside of the timing side flywheel for being drilled too deep and penetrating the oil galley. Found this on a Mototrans, probably loosing a little oil pressure there. Likely due to the less meticulous machining on the Spanish bikes but worth a look on any widecase crankshaft that's apart.

Matt

[DBDBrian]

This is all very interesting, It's my first "Ducati" crank, and I take your point Nigel re the clock location. I did check the oil nose, and there was no indication of ovality, perhaps I struck lucky.
Your bearing on the gear section is certainly the answer to a worn nose, but in my defence, "if" the nose is on centre, when running on the bearings, the end of the shaft would show the the greatest error.
Re the run out, we obviously strive for perfection, but in reality with a pressed up unit this is not in the main achievable, as said a compromise has to be made. I got this one to within half a thou at any point, and settled at that. The pin is up to the shoulders, as this is where the wheels returned to there original width before being split.
This is only for road use, so I think I will have to take the chance of a pin failure, but I bow to your greater knowledge on the subject.
Brian

Just out of interest this is a crank I made for my Goldstar, twenty plus years ago, not Ducati I accept, but it does have an Italian GM rod and parallel pin.

CRANK 1.JPG

[LaceyDucati]

Hello Brian

Sounds like your crank is a good one. There is usually a section of the oil nose right next to the thread that doesn't wear as it does not run in the bush, so that can be okay. Your Goldstar Crank looks nice, you are obviously a very competent engineer!

Regards Nigel

[DBDBrian]

Thanks for your kind words Nigel, I have often wondered if there is any of the legendary "Bill Lacey" coursing through "your" veins ?
Yes this particular crank seems too have survived the last sixty years remarkably well, I have another one which "is" 1- 1/2 thou plus, oval on the nose.
I line bored the new bush in the timing cover through the main bearings, so lets hope it survives another sixty.

Brian

[LaceyDucati]

Brian

No relation as far as I know, but I always get asked

The timing bushes are sometimes alarmingly out of line to the crank, hence their rapid wear. Line boring the cover through the mains is one of my tasks on any engine builds I do.

Unfortunately the pumps don't line up with the driving gear very well either! The slot in the idler gear is 4mm and the drive tang on the pump is 3.5mm, however many still bind up. This is not noticed by many and can only checked by assembling the components before the cases are assembled by feeling the rotation of the gear through the main. This is the reason the pump bushing wears rapidly and occasionally the pump tang gets worn/torn off This is where the aftermarket pumps really score, having an 8mm driving shaft and a 3mm wide tang. The 3mm wide tang allows for the misalignment and sure enough they never bind and nothing wears.

Regards Nigel