Crank to Cam dimension on 616 engine.

[Ibrahim Kuzu]

Jacques,
Are you reading my mind 8)

Craig,
Owners will do how ever they like design will accommodate the choices we have today....

Guys,
Please check the pictures:

For the time being, We are doing our regular late C/912 pump wet sump...Friends have choice to install what ever they like
Dry sump/Late VW etc....Machining the New timing cover Oil pump area will be choice ....
Thank you for all the great constructive advices...
IK

[Craig Richter]

You're way ahead of us, Ibrahim

[Albert Tiedemann]

Will have to take it to one hr away shop the case and the timing cover in future to read by high tech coordinate measuring machine ...
see what is the difference with our measurement...maybe do few cases and timing covers to see where the dimensions going...

This route follows my first response to this thread. Your measurement of 59.567 mm via hand tools and skills of a toolmaker in using same, is a magnitude different [by tool or gauge maker standards] than that which Jacques used, 59.68 mm, in the manufacture of replacement gears. By inference, the latter value was obtained from measured values from VW cases by unstated means. Because we are dealing with a pair of helical gears, the center distance can be varied considerably by adjustments to the helix angle [pitch angle stated in Jacques post]. And, if the helix angle [23.5 degrees] is not the same as that used in OEM manufactured cam gears, then the crankshaft gear[one size and one helix angle of opposite hand only] do not mate---theoretically.
Of course, if the crankcase timing gear is supplied to the same manufacturing inputs and the center distance is indeed found to be 59.68, then everything works including camshaft gears manufactured with profile shift coefficients of .01 increments corresponding to -1. -2 0 [shift = 0.00] +1, +2 to make up errors in machining center distances.

Jacques suggestion to use the dowel pin holes [as datums] to reverse engineer is very sound. In former times you would have referred to these as tooling holes.

Your endeavor to match the axial alignment of the oil pump driveR gear bore with the camshaft journal bores is an attempt to minimize the excursion of an Oldham coupling centerpiece if one were fit using the the tang of the oil pump gear and the slot machined into the camshaft as the "fixed" end pieces. The Factory realized the inevitability of a perfect alignment and opted for a "loose" fitting slot not only to ease assembly, but also "accommodate" errors. We have all witnessed the outcome of this command decision.

[Jacques Lefriant]

Hi Albert
The C/L distance we used was an artifact to engineer the gears. we had gear design software and maybe 59.75 is the blueprint value but with manufacturing tolerances the cases out there could be all over the place. our intent to to make replacement gears that would work, our "0" marked gears measured 5.202" and the +1 measured 5.2025" etc.
j

[Larry Coreth]

Jacque,

Counter intuitive ? Well I guess if you are thinking metal to metal contact and the teeth being squeezed together with no lubricant left between the teeth, then ues I see your point.

However on the other hand, too much clearance allows the cam gears to rattle or slap between the crank gear teeth, forward, then backward as each cam lob goes over center. The proof of this comes from the major error, serious "dope slap" required, I committed by me not measuring the cam gear clearance on a 616/2 motor I was building when I assumed the cam gear was the correct for the case in hand. Wrong !! After 50 miles I could hear clacking at idle that would diminish with RPM. After 200 miles it was really bad and diminished only some with RPM. At tear down the cam gear teeth were almost gone, battered to nubs and the sump was full of fine Alu powder mixed with the oil. The steel crank gear was also damaged with the same type of ponding marks, just not as severe.

I put a new cam gear (size "0") and crank gear in place and measured the clearance, way too much ! What I needed was a "+2" gear which was unobtanium from Stoddard, or from anyone else either at the time. I was screwed ! A local 356 enthusiast and friend rescued me, he had a used "+2" gear, Oh the Porsche gods be praised ! An all night session assembling the motor and I was off to the Porsche Parade in Wisconsin by the morning light, late and several dollars short. Been running well ever since.

[Ibrahim Kuzu]

Ab,
Thank you...
As you mentioned, Try to zero in a perfect C/L distance ( may never get a perfect one 8) due to manufacturing way of engine cases you mentioned ) so we may make a coupling to get that beating out from the cam slot on to the oil pump drive gear,( Like factory did for industrial engines ) you know those chipped metal pieces from corners of the oil pump shaft going somewhere.

My measurement is .70mm gap between oil pump shaft to cam gear slot...It would be great if this gap be reduced and also keep the oil pump shaft in the center perfectly....

We did use scanner on the timing cover and going over all the dimensions to make sure as close as factory...
IK

[Ibrahim Kuzu]

Craig,
Thank you but, believe me I am learning each step of the way since I started this things 10 years ago, Many experience engine builder friends and other designers of parts for the betterment of our 356 engines helped along the way....In our club web site so many useful info about our engines.

After reading the problem of the cam slot vs oil pump shaft and seen the damage caused over the years on the shaft ( picture Above posting )
You thing about it and say what can be done to eliminate this problem ...So I am trying to get to bottom of it, if it can be done..

Regards to this any opinions welcome...
IK

[Jacques Lefriant]

Hi Ibrahim
I believe we are stuck with this drive and there are no feasible alternatives.
a few comments.
In the engine lifecylcle new oil pumps and cams should be replaced periodically. Continued use will eventually result in loss of oil pressure causing more damage. Since the price of those items are prohibited "fixes" have been used.
1. Weld repair the cam slot and the oil pump drive.
2. industrial engine had a conversion drive piece that saved the cam and used a shorter pump drive.
3. new pump shaft(not recommended for DIY since the gear can come loose) or grinding the shaft to present a flat surface to the cam.
Anyway this problem is 356/912 issue and not a VW one. And i doubt that it will be a problem in the current rebuild cycle since there won't be enought use.
j

[Craig Richter]

J,
Don't tease, why isn't this a VW problem?

[Jacques Lefriant]

Maybe VW owners/shops aren't as frugal.

[Larry Coreth]

Ibrahim ,

If you are insistent and determined to improve the breed, and not redesign the whole lower half of the motor, may I suggest the following.
Since the wear rate is a function of force per bearing area, let's increase the bearing area !
If you make a new driven shaft for the oil pump but instead of a simple tab, make it a cross shaped coupling, added to this cut another identical slot in the cam end face perpendicular the existing one. By keeping the original clearance between the slot and the driven shaft, the original coupling concept and tolerances need not be changed.
This way you may get 200,000 miles out of the motor (at least the oilpump shaft) as opposed to the usual 100,000-150,000 miles !

That's my 2¢ worth !

[Jacques Lefriant]

OK Larry
how is this for elegant

[Brad Ripley]

anyone have a photo of what Jacques describes as
industrial engine had a conversion drive piece that saved the cam and used a shorter pump drive ?

[Larry Coreth]

OK Jacque you have topped me there ! That is nice !
Would you implant that coupling by shortening the pump drive shaft to fit it between the cam and pump with both pieces having tight fit to the original cam slot and drive shaft tab ?

Have you installed such a unit to date ? Good results ?

[Jan Balder]

anyone have a photo of what Jacques describes as
industrial engine had a conversion drive piece that saved the cam and used a shorter pump drive ?

Connecting piece shorter oilpump shaft to camshaft as found in a 616/33 industrial engine.

Jan.