Monday, January 7, 2019

2019 & another SPG crankshaft

Welcome to 2019.

Just before the new year began I found another SPG roller crank, this time it's an 82mm pinned unit with minor wear to the main journals and unused for many years.

As you may be aware (and contrary to a lot of folk who think SPG crank's are crap) I think they are fine if you use your brain and look after them. Yes, my 1602cc engine in the notchback right now has an NOS 74mm SPG roller I swapped 60 x semaphores for about 20 years ago! To be honest I did put 1000 km on the crankshaft as soon as I got it to see what it was all about and it is very impressive.

So why does the SPG come in for such a flogging? I think it's a little harsh to say these crankshafts are crap when the EMPI Inch Pincher (among other race VW's) was setting records with them back in the day. Very quickly, people worked out that due to the construction of the cranks (non splined joints), they did require pinning (look at the top photo to see evidence of this) to reduce the likelihood of the crankshaft from twisting when dropping the clutch at ridiculous RPM's and coupled to sticky rubber. Of course that was going to screw them up! It's a no brainer.

The other thing which does not bode well for them I am told (and I do agree) is that they do like to sit at reasonably high RPM's and not to idle them for prolonged periods of time which can kill the rod bearings. Why? It's all to do with the big end bearings and their oiling. Unlike a regular drilled crankshaft with passage ways from the mains to the big end journals providing pressurised oil, the SPG has no passages due to the pressed construction and relies on altered main bearings which have essentially slots cut (filed / milled) into them to enable oil to squirt out the side of the main journals into holes drilled on the cheeks (see the image above) of the crankshaft thus oiling the big end bearings (roller bearings) by a 'mist'. Yeah I think it's a bit crap and not ideal but it does work OK. I will keep the RPM's up and not race the notchback so it's no big deal.

So this 82mm SPG crankshaft - I saw it advertised locally and made inquiries. I am lead to believe this was originally bought back in the 1970's by a chap that taught me how to screw around with VW engines back in the late 1980's when I was young and stupid (I am now older and stupid).
Anyway, he bought it new, didn't do much with it and then it got sold to a well known chap here in Adelaide whom I believe did use it in a limited manner and then it went through another chap to the chap I bought it from just now. I am awaiting clarity around that story from the original purchaser but it seems I am correct and can trace it's history (my old boss from back then agreed it was correct). If so, it is cool to own another piece of Adelaide VW performance from back then and know it hasn't been overly abused.

What are my plans for it? Well nothing 100% at this stage except I have measured up the main journals and they are on the outer end of wear for standard journal dimensions which is a little sad so with that I took it to my crankshaft grinder man - Jim - who agreed to grind the main journals to suit a set of new main bearings (0.25mm) which I have now just received from Vintage Vee-Dub Supplies (
I have a brand new AS-41 case tucked away for just such an engine I had in mind for something like this as well as a set of NOS 90mm (no, not 90.5mm) NPR 'B' pistons and cylinders from the 1970's that were originally bought with a new Okrasa crankshaft back then. I have a number of other engine parts (as you may imagine) to go with all this and will begin the hunt for additional period correct items so the engine is 100% 1970's themed and visually correct.
The engine will not be installed in anything at this stage or even assembled but all measured up, machined, checked and boxed as a complete pile of boxes until I work out where it will go.

And in case your wondering about grinding a crankshaft like this - Jim the crankshaft man has ground one other SPG many years ago (also 0.25mm) the same way. You tie the rods together via piston pins (as per the images above) and then run a cable tie through the pins to hold them solid and not flap around. Simple as can be. And while on the subject of the rods, nobody can feel any 'wear' in the rod bearings so while this is not the way I like to do things (no measurement what so ever), I have always been of the belief that if you can feel wear in a bearing, the bearing is screwed and in this case I think I am in the clear with the rod bearings. A gamble of sorts but not the end of the world if it turns out that a bearing is naff as I can always slip a conventional 82mm crankshaft in there fairly quickly should that prove to be the case. I have swapped crankshafts out in air cooled engines previously over night in my youth so I couldn't care less to be honest! 

Fortune favors the brave as they say.

Some Notchback updates very shortly as the car nears the headlining stage and final assembly.

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Small updates on the 'S' assembly