Engine Assembly
- Greg Bryan
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Engine Assembly
I have been collecting parts to build a motor and thought it would be an interesting topic to see the step-by-step process - at least in the way I do it.
The motor is a '68 912 motor, but it is very similar to the later 356 motor used in the C and SC and is similar to all 356 motors.
I got this motor as a rebuildable core short block a few years back from Jim Callaway (RIP) and when I tore it down I was pleased that it was in good, albeit worn condition. The parts have been cleaned and refurbished, the rotating assembly balanced and it's ready to start putting it together. This case is from a '68 912 - two case halves and the third piece or front cover. On the right you can see the engine type 616/39 - this indicates USA 912 from the '68 model year - on the left is the sequence number - my understanding is that the factory stamped this number as each motor was added to the assembly line - this is the 112,280th "616" motor built from its inception. Harry Pellow used this number in his data base to determine approximately when the motor was first assembled. At the flywheel end, the factory stamped the case halves to ensure they kept the pieces that were machined as a unit together. On all 356s and early 912s, the third piece was also stamped with the same number. Sometime in early 912 production, the factory stopped stamping the 3rd piece. Either they had some way of keeping the 3 pieces together as an assembly after machining, or they were so confident of the precision of the machining that they didn't need to keep them together-third pieces were interchangeable. I have no idea of the exact reason. The engine serial number stamping on the third piece. This serial number scheme is unique to the '68 912 - this is the 3757 engine built in this series. You can see the casting date on the left and right pieces. This indicates January (one punch mark) of 1968, or about 60% of the way through the '68 model year.
PS - sorry that my iphone turns the pictures sideways - they straighten out if you click the picture
The motor is a '68 912 motor, but it is very similar to the later 356 motor used in the C and SC and is similar to all 356 motors.
I got this motor as a rebuildable core short block a few years back from Jim Callaway (RIP) and when I tore it down I was pleased that it was in good, albeit worn condition. The parts have been cleaned and refurbished, the rotating assembly balanced and it's ready to start putting it together. This case is from a '68 912 - two case halves and the third piece or front cover. On the right you can see the engine type 616/39 - this indicates USA 912 from the '68 model year - on the left is the sequence number - my understanding is that the factory stamped this number as each motor was added to the assembly line - this is the 112,280th "616" motor built from its inception. Harry Pellow used this number in his data base to determine approximately when the motor was first assembled. At the flywheel end, the factory stamped the case halves to ensure they kept the pieces that were machined as a unit together. On all 356s and early 912s, the third piece was also stamped with the same number. Sometime in early 912 production, the factory stopped stamping the 3rd piece. Either they had some way of keeping the 3 pieces together as an assembly after machining, or they were so confident of the precision of the machining that they didn't need to keep them together-third pieces were interchangeable. I have no idea of the exact reason. The engine serial number stamping on the third piece. This serial number scheme is unique to the '68 912 - this is the 3757 engine built in this series. You can see the casting date on the left and right pieces. This indicates January (one punch mark) of 1968, or about 60% of the way through the '68 model year.
PS - sorry that my iphone turns the pictures sideways - they straighten out if you click the picture
Greg Bryan
- Greg Bryan
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Re: Engine Assembly
This case has been cleaned and checked - it is standard and has never been re-machined in any way since it left the factory.
Notice that the oil galley plugs have been pulled for cleaning and to ensure that there aren't any goobers lurking therein. In this picture you see the main oil passage plug holes. See above for the galleys for the valve lifters and valve train that get fed by oil going up through the pushrods. Originally, these holes were made when the case was drilled for the oil passages. Once drilled, an interference fit aluminum plug was pushed into the case. In this engine, the holes were tapped and threaded plugs will be installed with sealer. I think some rebuilders will machine new plugs and install them as the factory did - i.e., with an interference fit.
On the flywheel end, one more main oil passage was drilled from this end.Greg Bryan
- Ken Tuvman
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Re: Engine Assembly
Looks like operating room cleansing standards - looks so professional!
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- Greg Bryan
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Re: Engine Assembly
Thanks, Ken - I am not a professional engine builder, but I have built maybe 20-30 of these engines over the last 50 years. I'm building this engine almost completely stock with the only upgrade are 1750cc pistons and cylinders. I also am using a different cam - Willhoit's WR58 camshaft that is pretty close to a stock SC or 912 cam.
Greg Bryan
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Re: Engine Assembly
Greg, one interesting difference is the oil cooler stand, which was machined by Porsche for vibration-dampening o-rings.Greg Bryan wrote: ↑Tue Aug 08, 2023 2:32 pmThe motor is a '68 912 motor, but it is very similar to the later 356 motor used int he C and SC and is similar to all 356 motors.
Jon Bunin
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Re: Engine Assembly
Here's a picture of the entire rotating assembly.
The counterbalanced crank is the one from the engine short block and may be the one that this case was originally built with. The crank is first undersized and was when I got it. It measures good -in spec for first undersized so I didn't turn it again as at first under, some of the nitriding treatment remains.
Rods big ends are resized and piston pin bushings are new and sized as well.
The cam gear is used but in good condition, the distributor gear in not damaged and is being reused.
Good uncracked pulley.
All rotating parts are balanced as a unit - not shown is a new clutch cover that is indexed and balanced with the flywheel. Rods are balanced too.
PS - new first under rod bearing are German KS brand. Main bearings, standard case/first undersize crank, are from AA Precision Products.
Flywheel has been resurfaced but otherwise stock. I have a new SCAT gland nut and a Wolfburg West Viton main seal. The counterbalanced crank is the one from the engine short block and may be the one that this case was originally built with. The crank is first undersized and was when I got it. It measures good -in spec for first undersized so I didn't turn it again as at first under, some of the nitriding treatment remains.
Rods big ends are resized and piston pin bushings are new and sized as well.
The cam gear is used but in good condition, the distributor gear in not damaged and is being reused.
Good uncracked pulley.
All rotating parts are balanced as a unit - not shown is a new clutch cover that is indexed and balanced with the flywheel. Rods are balanced too.
PS - new first under rod bearing are German KS brand. Main bearings, standard case/first undersize crank, are from AA Precision Products.
Greg Bryan
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Re: Engine Assembly
What are your plans for the motor? Is it going into a 356?
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former 1966 Euro 912 Sunroof
former 1978 Intermeccanica Speedster w/'68 912
Member Since 1983, #4039
"Nostalgia isn't what it used to be"
- Greg Bryan
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Re: Engine Assembly
Yes, true - I think that was introduced sometime in the '67 model year, but not sure. I will use an aluminum cooler bolted directly to the block without any of the flex parts. My understanding is that the o-ring mounts were only partially effective in preventing cracks around the oil cooler mount.Jon Bunin wrote: ↑Tue Aug 08, 2023 3:11 pmGreg, one interesting difference is the oil cooler stand, which was machined by Porsche for vibration-dampening o-rings.Greg Bryan wrote: ↑Tue Aug 08, 2023 2:32 pmThe motor is a '68 912 motor, but it is very similar to the later 356 motor used int he C and SC and is similar to all 356 motors.
I'm sure there are other differences, too. One I can think of is the third piece is redesigned for the rear mount for the 912 powertrain.
Greg Bryan
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Re: Engine Assembly
I have a 912 project car that it will go into for a while anyway. I am also contemplating a hotrod type 4 motor or a 1925cc 616 motor for the future. I'd like to do a 2.2L but out of my price range
PS - I have a 1900 912 motor in my 356 and the original motor on a stand in the garage.
Greg Bryan
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Re: Engine Assembly
What bore and stroke is the 1900?Greg Bryan wrote: ↑Tue Aug 08, 2023 3:54 pm PS - I have a 1900 912 motor in my 356 and the original motor on a stand in the garage.
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- Greg Bryan
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Re: Engine Assembly
Stock stroke, 90mm bore - actual displacement is 1883, I think.C J Murray wrote:Tue Aug 08, 2023 5:16 pmWhat bore and stroke is the 1900?Greg Bryan wrote: ↑Tue Aug 08, 2023 3:54 pm PS - I have a 1900 912 motor in my 356 and the original motor on a stand in the garage.
I was rounding up …
91mm barrels with stock crank give 1925cc
Greg Bryan
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Re: Engine Assembly
How did you clean that so well?
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Re: Engine Assembly
Greg, did you rebush the rods yourself? Where did you have the balancing of the bottom end done?