I thought this engine was worth having a look at and kick around in the forum. I've seen inside more pushrod engines than I care to talk about, but this situation was new. In the summer I was assisting Jim (Woodenshoes) tuning his 122S and noticed that when he cranked the engine, the crank pulley moved quite a lot.

https://youtu.be/5GAhyM8ZZfk

The video is how Matt and I sometimes communicate - ha, ha. Now every engine I build I check the thrust clearance and they have to be very tight (like 1 - 2 thou tight) - not visibly moving. There were also issues with tuning this engine as the carbs (fresh rebuilds) wouldn't play nice. Now, this engine was one of the big buying points for Jim for this car. It was supposedly full of all the best stuff IPD has (dual valve springs, HD oil pump, header, VV17 cam, high rev kit (Chevy lifters and longer pushrods)) - you get the idea. Hot stuff and just being rebuilt it looked like a winner as I would charge almost what Jim paid for the car to rebuild the engine to this specification.

The first time I drove it, Jim wanted to know if it had similar power to my 122 with the B20 - my blunt answer was NOPE. It's hard to diagnose why - the engine seemed happy enough, but there wasn't much snap to it. It should have been better - we thought it was carbs and tune related. After seeing that thrust bearing - I was suspect of the rebuild.

So fast forward about 6 months and we're pulling the engine.

With a rented engine hoist large enough to yank a tractor motor...we pulled the engine out this week. Things were not looking good when I pulled the transmission off and the pilot bearing fell on the floor. No one had installed the oil slinger or the clip. Not really a great sign of the care and attention to detail needed when assembling engines.



Then with the head pulled, we can see that cylinder 3 - 4 were along for the ride. 1 and 2 look like they were running fine.



It did have new Mahle pistons and steel timing gears and the HD oil pump so at least the basic parts are sound. 3 - 4 exhaust valves are recessed inside the head (the valve margin is level with the head or inside the head). So the exhaust seats are done but the valves are new as are the guides and it does have the double valve springs/high rev kit. So new valves and seats are needed. These issues were also confirmed by the lack of compression on 3 - the valves were leaking. So running on 2 cylinders in essence.

Next we whipped out the pistons and found that the lack of thrust bearing had caused wear in the bores in line with the cylinders. They usually only wear perpendicular to the main line of the block. It was easy to see, hard to photograph. What we saw was the "back" of the cylinder had deep cross hatch from honing evident and the front had almost none.

Back



Front - you could see some hone marks with the flash light, but almost non to the naked eye.



Flipped the engine over and found...horrors.



Those fragments are thrust bearing material. You can see that the bearing is missing from the rear of the #5 main bearing shell.

So out comes the pistons and crank. Yikes - this isn't good news.



Some bearing material has gotten itself embedded in the rod bearings - they're now junk.



This is the wear on the thrust journal. Not sure if this can be welded and repaired, or if Jim's looking for a new crank.



So that's the tear down. Here's my analysis. First, the thrust bearing is often overlooked when reconditioning a crank or when enthusiasts are building an engine. It's critical - just like all engine parts. Then the question "How did this happen?" must be asked. My first observation was that while the engine had been rebuilt, corners were cut. The block of the deck wasn't cleaned up (they are normally wavy and need at least a fresh gasket surface to mate to) and one of the head bolts was rusted (slight HG leak). The fasteners on the engine were loose...like the rear main seal was on finger tight. So we're dealing with some hack job rebuild.

The main line was bored but there was no hatch as you would expect from a proper honing. I don't normally hone the main line as these deep skirted blocks rarely come out of line and if you don't need to touch the factory work, I don't. So someone thought this was a Chevy V8 and line bored the block - no hone. This, in my analysis is how the bearing went bang.

The thrust bearing is present to ensure that thrust loads are contained, if the main line is not perfectly perpendicular to the bores, then the thrust bearing is placed under undue load. They can also fail due to excessively coarse surface finish (a reground crank with spiral finish on the thrust face is not good as the groves wipe the oil from the bearing and cause failure) - but Jim's crank is standard size, so that's not the issue. I'm willing to bet that the main was bored a little crooked. These things should never need boring - just a hone (I've done only one ever) - a few thou is removed from the caps, they are replaced and a line hone is run though the engine to hone it to size.

The block is salvageable with a light deglaze and deep clean (it was very dirty) we're ready to go. Then with new valves and seats the rest is fine. So a top and bottom gasket set, new cam (it was on it's way to wiped) and hopefully a new crank and this one can be buttoned back up and be ready for the driving season.

Is this from the 122 I went and looked at?

If it is. I'm really sorry.

Unless you or Matt grabbed it, I should have a 6-bolt crank sitting on a shelf in my overcrowded garage...

I think you had an 8 bolt marine crank, Dale, didn't you?

Craig, many thanks for the help pulling and disassembling the engine as well as the detailed diagnosis presented here. I could have updated my build thread with the details but it would not have been as thorough nor informative.

Jordan, no sweat man, I asked you to go look and put an eyeball to it to see if it was worth pursuing from afar. Not having a proper PPI done prior to purchase falls on me, and me alone.

Dale/Matt, the crank is going in to the machine shop tomorrow morning for measurement and the final word on it's fate. If you can guys can confirm any useable cranks in advance that would be much appreciated, obviously hoping mine is salvageable but...

No problem Jim - good on you for taking this on. If it's an 8 bolt crank, I've got a flywheel sitting around somewhere. So we can cover that with any 8 bolt flywheel. They're all the same.

I still have to get a list of parts together for you.

Let's do that here.

First from http://www.kgtrimning.com/ I would suggest the KG-17 cam (lifters can be bought locally), they can also supply exhaust seats, 38 mm exhaust valves and 44 mm intake valves (Intervalves is the brand). You'll be dealing with Fredrik - his English is fine. I'd also ask them to pull a B20B or B20E headgasket (try to get one with 30 thou or so thickness squished - tell him what you're looking for) - if he can't, we can get a Cometic MLS gasket at the machine shop for $150), Top and bottom gasket kit and the front and rear seals from a 240 (B21 seals are what you have for front and rear main seal.
Their price for the main and rod bearings are about what everyone charges, so I'd make it a one stop shop. At this point you can't order anything as we don't know about the crank. So let us know how it all works out when you return from the machine shop.

If the KG-17 isn't available - the TT-4 is from Tinus Tuning (http://www.tinustuning.nl/1-onderdelen-upgrades.html) - again English is no problem with Ben.

If 8-bolt, why not go big bore? I've got a couple of big bore head gaskets around here. B21 pistons and rods aren't that tough to find. I still need to get the energy to get out to the garage and look at that crank...


...and...as usual, Matt knows more about what's in my overcrowded garage than I do. It is indeed an 8-bolt crank. I can't think of anything I'm ever going to use it for...

Thanks Craig, this whole situation is a kick in the teeth considering what I thought I had, but I'm really getting in to this and looking forward to putting together a great little engine. Not moving real fast today so heading out in a bit to PP with the crank.



This sounds like scope creep at it's finest... I love it!!

Will report back as soon as I get word from the machine shop.

The biggest reason to not go big bore (aside from no one in town can sonic check a block) is that Jim's pistons are essentially new and another set of B21 pistons is $500 plus the cost to bore the block oversize. The biggest issue at this point is getting the main honed and checked to make sure we don't start to loose clearance with the cam gear at the crank comes up in the block. Have to be very careful with lash on the gear train.

Delivered the block today and the crank on Monday. The machinist said they are looking for an oversize thrust bearing to take up the amount they need to shave off the crank to level out the gouges. Craig, I mentioned that they could contact you as they were trying alternative sources as the regular supplier didn't have what they needed. Other than that he thought the crank was in great shape.

His initial thoughts on the block were that it was going to be OK and that the mainline would be square to the bores. He was leaning more towards a misalignment of the thrust bearing on assembly or possibly the pilot bearing not stabilizing properly for the thrust bearing failure?? He actually spent quite a bit of time going over everything which was very helpful.

Can someone fill me in on how a pilot bearing could do this? How would you misalign the thrust bearing when it was installed? Unless it was manufactured incorrectly. I've also never heard of a wider bearing as this is so uncommon. The thrust loads on an engine are not generated by the transmission.

Hey Craig, any chance you could give them a call to check on what's going on with this wider thrust bearing? What he was talking about seemed to make sense, but what do I know...

If he can find a wider bearing then you're fine. I understand that the thrust (axial) forces can be generated by the transmission/clutch, but I always figured with the size of the thrust bearing, there was more than ample bearing to deal with this load. That said, there was evidence on your flywheel of heating and a degree of abuse (the radial cracks).

My thoughts about the mainline straightness stems from my initial observation of what happened when the engine was cranked. It was clear that the thrust was gone. The helix on the crank/cam gear pulls the crank to the front of the engine and the cam gear towards the back of the engine. The motion observed on the crank pulley was very consistent just like one would imagine would happen if there was no resistance to to the force of the crank gear (only being turned by the starter). It's not like the thrust bearing was worn - it was gone to the rear only. So the force was towards the front of the engine only.

I can see it being worn if it was transmission/clutch wear, but more evenly as you're engaging and disengaging the clutch. Now the clutch and pressure plate were miss-matched. Not sure it that would present an issue.

If the mainline wasn't straight then an additional load would be generated by piston motion. Maybe it was just a faulty bearing.

I killed THREE main thrust bearings in my 302 in less than 2500 km, an engine that historically has zero troubles with main bearings. It also doesn't have a helical drive on the snout pulling the crank forward all the time, and I know my pilot and throwout bearings were good, as was my transmission alignment. I had the engine line honed, which is the only thing I can think of being the problem. I'd checked the deck height on all cylinders after machining and before decking, and they were PRETTY consistent - the crank was a little twisted in the block IIRC, but only by a couple thousandths. The block & crank had gone 800,000 km before that in a taxi cab, so I know they weren't a problem before.

Jim, there are other cranks if you need them. JP has engines and while they won't be free, I'm guessing one will come at good guy pricing due to association with Craig and myself. Problem is, if the main line IS the problem, it's your block that I don't trust - not the crank.

Thanks again for the observations both of you, it's starting to kinda make sense... As soon as they call on the block squareness, or lack thereof, (hopefully not) I'll update and we can figure out the next steps.