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Second Engine Rebuild 323i

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e21Keith
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Posts: 333
Joined: Sun Jan 05, 2014 7:44 pm
My E21(s): '81 323i Manual

Second Engine Rebuild 323i

Post by e21Keith » Thu Aug 01, 2019 4:18 pm

As posted elsewhere I have a knocking big end after my weekend at Silverstone, the car has done 700 miles since the rebuild and considering it's built mainly from 38 year old parts I was expecting there may be some issues, even after having to replace the head due to a crack. I suspect one of the rods or the crank are oval and have been so since the rebuild.

I will send the crank and rods away for checking and machining but I'm wondering whether I should do something with the pistons and bores? There was some wear on the bore of number 6 but nothing excessive and it doesn't seem to use any oil, but while I'm there.....

From what I understand new pistons in oversize are not available except if I have them made. Also new standard pistons are available but the cost doesn't seem to be any lest than having them made. I have a spare 320 block so boring out and having standard 323 pistons is I believe an option.

What are people's experiences, any advice, what should I do?



shadyracer01
Upcoming E21 fanatic
Posts: 62
Joined: Tue Dec 05, 2017 7:39 pm
My E21(s): 323i '82 Y x2, 1 in resto, 1 now spares

Re: Second Engine Rebuild 323i

Post by shadyracer01 » Sun Aug 04, 2019 1:56 am

Hi Keith, glad you made silverstone with it but bummer if it has run a big end. Id hope that from what youve described that a new set of shells and honing of the bores would be enough to rectify this, especially with the piston replacement costs. I will see if can find shell set part numbers for you std and oversize. Have you done a compression test on this engine ever? That would help knowing the values to decide how to proceed.
I havent had any experience with these engines internally yet other than oil pump and tappet setting up so cant advise you but do hope somebody here can.

e21Keith
E21 Fanatic
Posts: 333
Joined: Sun Jan 05, 2014 7:44 pm
My E21(s): '81 323i Manual

Re: Second Engine Rebuild 323i

Post by e21Keith » Sun Aug 04, 2019 8:40 pm

Well I've done a bit of research.

Bottom end I'm looking at a regridg with undersize bearings which are available from W+N if nobody else does them, so that's not a big issue, just slightly costly. I would have to get all the rods checked for ovality as well.

The next question is do I just leave the pistons and bores alone as they seem ok, not burning any oil etc, or should I go the whole hog this time? I can't find oversize pistons but I can get them made at a cost of $900 (plus shipping and probably some import duty), I could then get my block rebored

The 320 and 323 block have the same bore and I have a 320 block which I think is good, maybe I could have this honed and fit my old pistons?

Does anybody know what the differences are between the 320/323 block, can it be used if the bores are OK, what do I have to do?

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