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Round 1, Fight!
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peterld  



Joined: 10 Dec 2006
Posts: 846
Location: Noosa Heads QLD Australia

PostPosted: Mon Jan 25, 2021 11:00 pm    Post subject: Reply with quote

Have the block hot-tanked and then rebuild it.
Everything looks OK. Measure carefully, then new rings/bearings/gaskets etc. Maybe consider a very light hone of the bores. Slight excessive piston to bore clearance can be taken up by ceramic coating the piston skirts.
Similarly with the head. Have it cleaned then lap valves/seals/gaskets etc.
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Alleycat_Joe  



Joined: 14 Sep 2020
Posts: 15
Location: Florida

PostPosted: Tue Jan 26, 2021 3:35 pm    Post subject: Reply with quote

peterld wrote:
...Measure carefully, then new rings/bearings/gaskets etc. Maybe consider a very light hone of the bores. Slight excessive piston to bore clearance can be taken up by ceramic coating the piston skirts.
Similarly with the head. Have it cleaned then lap valves/seals/gaskets etc.


Thanks! That answered a lot of my questions.
Are 931 and 924 piston rings the same? It looks like Grant rings are the most affordable and initial research shows they're cast iron and are reliable. Any downsides to that brand if I plan to do an actual engine build in the future?

I took measurements of the bores at the top and middle, front-to-back and side-to-side. I took a picture of my calipers from the largest bore measurement for "digital enhancement," as shown below:



ENHANCE!



Upon closer inspection it looks like my largest bore diameter was in the range of 86.58-86.61mm. Given I'm honing group 602 (86.52mm) and 0.08mm is the wear limit, boring and oversized pistons are technically required, but since my compression test was within spec for that cylinder (#2), I'd rather save that for a year or two down the road, maybe get a second engine to build over time. I'm hesitant to try ceramic coating the piston as I don't have a lot of funds to send them off or buy the sandblaster to prep the pistons for coating at home. Has anyone here successfully ceramic coated pistons at home without a sandblaster?

Fun fact: cylinder 3 has the least wear.

The connecting rod with the most side clearance was 0.279mm, well within the 0.4mm wear limit.

The kicker though was the crankshaft end play, which measured to a whopping 0.736mm! The wear limit there is 0.25mm, so I guess I need a new journal bearing, therefore a new bearing set like
peterld recommended.

There was no radial play in any of the bearings (by feel) so I'm surprised the crankshaft end play was so drastic. Here's a picture where I measured so please correct me if I measured wrong:





Maybe this is the damage I caused with my "double-crowbar underhand backside kick" maneuver when trying to separate the driveshaft from the crankshaft while under the car? (Edit: not likely)

Heartfelt thanks to everyone who set up and participated in the bearing group buy in 2009; it looks like ebs-racing still sells them today, probably because of those individuals!

Edit: Well here’s my problem.



The thrust bearing is worn completely flat on the front, and it has worn a groove into the crankshaft (where the crankshaft touches the thrust bearing on the front).





I was unable to get a precise reading on the depth of the wear on the crankshaft, so hopefully it’s in the realm of <0.1mm.



I measured the thickness of the bearing faces (~1mm on the back and ~0.5mm on the front) so the front face is worn in the range of 0.540mm +-0.133mm. Hopefully this is where the crankshaft end play originates, and if I install a new thrust, endplay should be within the wear limits. I’m worried however that I need a new crankshaft, because of the groove in the crankshaft. I plan on plastiguaging the other bearings, and if everything else is within the wear limit I found a source for a new thrust bearing alone. I may just replace the thrust bearing alone and use this motor as a test bed for the EFI set up while I gather build parts for possibly a second engine. Thoughts?

Edit 2: I removed all the bearing caps and decided to go ahead on a full bearing set, as most of them had some scoring. Luckily all the journals looked great, considering the lack of maintenance this engine saw. This is the only way for me to determine if I need a new crank. Surprisingly the rod bearings and journals looked healthier, but still had a couple grooves. I plan to file a relief cut on the thrust bearing to allow extra oil to reach the front thrust surface. Hopefully this will mitigate the wear issue without significantly impacting oil pressure.

Edit 3: Thrust bearing clearance is in spec! 0.051mm on the journal surface and 0.189mm for crankshaft end play! That leaves me at 0.061mm before the end play wear limit but it’s good enough for me to run this crankshaft.
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Last edited by Alleycat_Joe on Fri May 21, 2021 12:26 pm; edited 2 times in total
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Alleycat_Joe  



Joined: 14 Sep 2020
Posts: 15
Location: Florida

PostPosted: Sat Feb 20, 2021 9:15 am    Post subject: Reply with quote

Still hard at work here, I've put in around 20 hours since the last post cleaning and checking tolerances. So far nothing bad except warpage in the head and block. Block is within spec but this engine was clearly overheated, since the head is way out of spec, which explains the fan switches in the mess of wiring under the dash.
Every first piston ring was broken in at least two places, one piston even had four separate pieces flinging around. Make that another case for bad S1 ring design.



The valve keepers were an absolute pain, requiring a hydraulic press to remove. That's normal, right?



One piston had metal debris embedded in the side, causing deep scoring on the wall. Wild stuff.




I filed down the valve damage on the piston heads, it had been left to hot spot and attract detonation by the mechanics who replaced the valves. There is evidence of detonation on pistons 3 and 4 between the valve indents. Everything seems fine to reuse, aside from bearings.



Also what the hell holds some of these paper gaskets on their surfaces? Seems like they're bonded on a molecular level or some shit. Had a time trying to clean up the oil pump.



Corrosion in the block has been addressed with a vinegar bath and wire brushes. Pretty happy with the results, but I only have a "during" picture.


Sadly, seven of the EBS Racing bearings were damaged during shipment or manufacturing, but they sent replacements ASAP, which was nice.



All-in-all good progress, but this is a lot more damage than I was anticipating based on my discussions with the seller. It's a good learning experience and I have the time, so I'm grateful in the end, as long as I can get done within the year.
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Alleycat_Joe  



Joined: 14 Sep 2020
Posts: 15
Location: Florida

PostPosted: Thu Mar 04, 2021 7:00 am    Post subject: Reply with quote

Title acquired and transferred into my own name! Let the spending begin!
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Mike9311  



Joined: 14 Dec 2004
Posts: 1146
Location: Chicago-ish

PostPosted: Thu Mar 04, 2021 8:27 am    Post subject: Reply with quote

I'm watching so keep it up!
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1980 931 since 1989
1981 Ideola 931 Club Sport
1982 931 Entwicklungsfahrzeug
1979 924 NA M650 Herausnehmbares Dach
1982 931 Red Resurrection - 951 IC
1982 931 parts car / resurrection?
1980 924 NA (R&D lightweight)
1982 931 wana-be GTR race car
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Alleycat_Joe  



Joined: 14 Sep 2020
Posts: 15
Location: Florida

PostPosted: Fri May 21, 2021 9:38 am    Post subject: Reply with quote

Mike9311 wrote:
I'm watching so keep it up!


Thanks! I've been busy on the car and sourcing parts so an update is due.


I goofed the final exhaust valve during disassembly of the head and didn't find out until I was lapping the valves before reassembly.




I cleaned all the axles and repacked them with fancy grease.




I modified the distributor into a single tooth cam gear, but still have to mount a sensor and test.




I made intake and exhaust manifold studs and a block off plate potentially for a boost port.




Went to the junkyard for hatch struts (95 jeep cherokee) hood struts (13 Chevy HHR) Throttle body (06 Audi A6) TPS sensor (04 Land Rover Disco) and a smart Coil Pack (05 VW New Beetle 8v)




I modified the throttle body with the original porsche cable mount and a custom bracket to mount the Disco tps. The audi tps was too large and the shaft was too long so it had to be cut.










Edit: The throttle port on the intake manifold will need to be enlarged for the larger 52mm butterfly valve and the offset on the 35mm valve. Original sizes were 35mm and 44mm, so at least all this effort is a decent upgrade.




I also honed the cylinders a little, barely scratched them but it's hopefully enough to promote ring sealing. The cylinders ideally would be bored but I'd like to see how many miles I can get out of the engine without a machine shop or buying new pistons. Just piston rings for now.



As it sits, I still need conrod bearings and no viable source had been identified. Since I am not expecting much from the motor at this point, I may simply reuse the original bearings as long as they are within tolerance. I also have to source conrod bolts. Then it can all be reassembled and tossed back in the car with everything else.
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MikeJinCO  



Joined: 08 Jun 2010
Posts: 1039
Location: Maysville, Colorado

PostPosted: Fri May 21, 2021 9:07 pm    Post subject: Reply with quote

Apparently Mittlemotor in Germany has the worlds supply of standard size con rod bearings
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Poco a Poco, #033 '78 Vintage racer, SCCA Dp-81
'77 924
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peterld  



Joined: 10 Dec 2006
Posts: 846
Location: Noosa Heads QLD Australia

PostPosted: Fri May 21, 2021 9:53 pm    Post subject: Reply with quote

What about trying Coco-Lev who posts on here?
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