mark kibort

based on an old 928intl catalogue, it seems that the main bearing sets for the older 2 valve models, is based on engine serial numbers

There is a single piece front main bearing or the older 2 halves for that front bearing. The challenge is figuring out which one to order.

my (Scot's) engine is an M28-11 and has a serial number of 8200778
The little 928 book shows 82C XXXX. Anyway, im almost positive i need the 2 piece bearing set, but how do you know for sure?

thanks

Mk

Vilhuer

On upper half of the block there is small stud which holds single piece bearing from rotating. On two piece bearing block #1 bearing area should be similar to all other 4 mains.

Mike Simard

Here's a pic of that dowel for the one piece bearing

Vilhuer

Also shows feed hole for piston squirter.

mark kibort

Thanks guys. thats what i suspected. is there any difference in the thrust bearings?

what is that front bearing picture? hard to see what im looking at.

by the way, my 84ish crank, as i assume it's an 84 as it has the bigger oiling holes but the weight was off by as much as the new 5 liter pistons were heavier, rubs on the block. (i posted this information awhile ago) ive ground down the crank to not hit the side of the thrust bearing area of the block. seems odd that all the cranks woudnt be the same, but they are not.
so, warning..... Old block, new crank.

Mk

Mike Simard

Here's the whole pic. It is confusing because of the holes for the squirters (87 block) and the machining for the sleeves but it does show that dowel in the front specific to the one piece bearing. It would be interesting to know if your block has the dowel sleeve around the front stud as well. Porsche drills a stud at the front and back of the block to have a locating sleeve. At some point they stopped installing the front sleeve, possibly because the one piece bearing acts to locate it laterally? The manual does instruct installing the oil pump during case assembly which provides longitudinal alignment. BTW, the main bores are to measure 2.9528 - 2.9535. The manual doesn't list any different main bearing sizes or thrust widths for certain years.

mark kibort

Uhhh, sir, you are missing your cylinders

Great shot! thanks. absolutely, I (scot) have an early block. no dowels. only the tell tail cut outs at the corners of the bearing area for the separate front main bearings, like you see on the other mains toward the rear.

turns out, just found out that the bearings changed in year '82, and anything older is separate mains in front bearing area.

thanks,

Mk

Vilhuer

Height of the thrust bearing sides were increased in '82-83 time period IIRR. This meant that crank also got taller side areas which are machined to be counterparts for thrust bearing. Not sure without checking if this was done at same time as oiling hole diameters were increased in crank. It should be possible to use old style crank with new style block without mods. New style crank in old block can mean small changes to block in areas surrounding thrust bearing.

mark kibort

Here is what happens with old bock and new crank like you noted below in your message.