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PostPosted: Sun May 09, 2021 12:22 pm 
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SpaceFrank wrote:
This post got me thinking about the history of slant six failures in Lemons. I'll record what I know for posterity. Warning: incoming wall of text.

EVR has "killed" a total of four slants in eight years of Lemons racing. We've never revved one higher than about 4800 RPM except for a couple accidental downshift incidents.
1. Red 1 (original 1964 block): Rebuilt by a small, quality shop that didn't know much about slant sixes. Drove ~20,000 miles and then 5 endurance races. Still ran and made good oil pressure when we pulled it, but the blow-by was so bad we actually lost our dipstick on track. Rings were all in pieces; I'm guessing they were gapped for street driving and then closed up during one or more overheating incidents before we put a decent radiator in the car.
2. Red 2 ('64 block): Pulled out of a Craigslist car (now the "Art Car") and slapped right into the race car. We never should have raced this engine without at least cleaning out the oil pump relief valve, but we were dumb and in a hurry. It didn't make good oil pressure and threw a rod after about an hour on track.
3. Red 1, Part 2 (rebuilt original block): Quick ring and bearing job done by a couple drunk monkeys in a garage. Rings gapped wide. The head got a deck job and then big valves after we won Lemons Class C. This engine ran great for 9 endurance races despite repeated blown head gaskets (primarily due to us not doing our homework on ignition timing when increasing SCR) and also ingesting a carb nut. It was only retired because we cracked the water jacket early in its rebuilt life, either during a hard freeze at the cancelled ECR 2016 race or after our last blown HG went into the water jacket at CMP 2016.
4. Blue ('73 block): Stock. Ring and bearing job again performed by two drunk monkeys in a garage. This engine always ran hot because we are stupid, and our decent aluminum radiator was now clogged with 3 cans of Barr's leak after racing the cracked Red block for so long. It survived for 3 endurance races, and then we blew a bunch of ring lands off (pretty much on purpose) with a badly-tuned blow-through turbo.

The Resistance (our quasi-sister team from Austin) has only killed one engine that I know of, and it's the one mentioned in the above Youtube video. It was a cast-crank block, and I believe it was the one in the car when they bought it. No idea about its operating conditions, but after surviving one full 24-hour endurance race (MSR 2018) it started knocking on practice day at NOLA 2019. They acquired the "Bud" engine the next day, which was one of the transition-year blocks with a late casting number but a forged crank. They decided to save it for a proper rebuild, and slapped new rod bearings in their knocking cast-crank engine after sanding the rod caps down. It blew up about 12 laps later, but it still drove onto the trailer.

Jason's Valiant killed one engine I know of, but that was from eating an entire bolt. Somewhat larger than the 1/4"-20 nut that banged around in our engine for most of a race day. I know the Slant Six E30 killed at least one engine, but y'all would know the history on that car better than I do.

Dudes Ex Machina, a California Lemons team run by a forum user named mackwagon, had some issues with their slant six, but I don't know much detail. I seem to recall him mentioning overheating issues, and I know at some point they installed an Accusump system for oiling. Based on one old post I found, it seems they were running up to 5500 RPM regularly with a built "long-rod" engine.

Squatting Dog Racing, another Lemons Team, blew up a slant in their Valiant back in 2015, but the race summary article blames it on overheating when they lost a fan belt. It also sounded like the car was a field-find with the original engine, so who knows what its original condition was.

The Oly Express team from Washington state ran a slanted '64 Barracuda for a while, but they eventually switched to a V8. Not sure what troubles they had with the slant, if any.

Anyway... what I gather from all this anecdotal data is that if you want to keep a Slant Six alive in road racing, you need to keep it cool, well-oiled, and below 5000 RPM. Big surprise, I know.


I can add to this with Valiant Effort's failures on the west coast in our 63 V200.

Race 1, 74 motor refreshed but not rebuilt. Stock cooling system, Thunderhill raceway, 116 degrees out.. We could only keep it cool by running about 1/3 throttle and religiously watching the gauge. One driver forgot to watch the gauge and brought it in with the gauge pegged at 250. We got it cooled, changed a head gasket and ran the next day with low compression and no power but it "ran" for another 50 laps or so. We did a full rebuild after this race and also replaced the original tiny radiator with one from a later AC car. We replaced the 4 blade fan with a large electric fan as well.

Race 2 - No issues

Race 3 - Sonoma Raceway, Car was running great and the fastest we'd been when we came in to pit the brakes were smoking hot.. Next driver went out and reported a bad vibration, we then noticed the wheel weights had fallen off from the heat when we stopped to pit. 2 laps with that bad vibration sheared off the air cleaner stud which went through the #5 cylinder and destroyed it. 0 compression and glitter in the oil. We pulled the plug from #5, change the oil and ran another 72 laps until it was rod knocking so badly we had to call it. Full rebuild afterwards, same block, now bored 60 over, mild cam, 2 barrel intake, oiling improvements Dutra recommended. MSD rev limiter set at 5k.

Race 4 - No engine issues but we cracked the A904 circumferentially all the way around the bellhousing area. The car ran perfectly all of day 1 and this somehow happened when it cooled off overnight. Lap 1, day 2, huge vibration and we found the problem and were done. Rebuilt another A904 using V8 guts in slant case and it has worked great since.

Race 5,6 - No issues at all, car ran great. Only the drivers need improvement..

Race 6 - Engine still running great

Race 7 - Sonoma a few weeks ago, Car still running great but the original 7.25 rear finally succumbed to that slanty power and fully melted down and grenaded. All the gear teeth from the pinion came off. Time to build the early B-body 8.75 I have for it and upgrade to LBP brakes. Engine still running great, compression test was same as post rebuild +/-3 psi on all cylinders in our post race checkup.

-Jon


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PostPosted: Sun May 09, 2021 4:51 pm 
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Very cool thanks for sharing Jon...

Are there any other west coast slant 6 teams / cars?


Greg

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PostPosted: Wed May 12, 2021 12:45 pm 
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Thanks for the info, Jon!

Looks like my Lemon isn't the only one breaking slant A904 cases. One cracked the bell housing area so bad that the assembly flexed, and it sheared all the flex plate bolts off. Our current one we just noticed a crack coming from one of the forward pan bolt holes, of all places. Bob and I are talking about building a ladder-frame support cradle to go from the trans mount all the way up to somewhere on the engine block (or maybe the engine mounts) that would support the trans case along the sides of the pan rail. I don't like the idea of 60s-era cast aluminum being a structural member in bending, especially with the added vibration from road racing.

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PostPosted: Wed May 12, 2021 6:00 pm 
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I am surprised that road racing is that hard on the 904 cases?? Seeing how guys are running them in really fast drag cars with trans brakes. Must just be a different kind of stress.

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PostPosted: Wed May 12, 2021 7:53 pm 
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Running for 6-8 hours straight can be more harsh than say 20 seconds at a time in a racing situation.

One of my 904's broke when the driveshaft came loose.. remember that one Rick?!??!!!

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PostPosted: Wed May 12, 2021 9:21 pm 
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Are folks breaking cases running without the block brace on the left side?

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PostPosted: Thu May 13, 2021 2:17 am 
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Good point, Josh. I always run one even when I broke mine but when you have a driveshaft whipping around at 5000 rpm the bell housing was no match for that shenanigans and broke.

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PostPosted: Thu May 13, 2021 6:48 am 
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Yes, you absolutely need the block brace, bolted tightly. I am wondering if vibration could be the problem? I've never had trouble. I also bet that overtorquing mounting/mating bolts, within reason, would help.

Lou

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PostPosted: Thu May 13, 2021 8:58 am 
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I have tightened most of the bolts on the 904 tighter than required... i use a helicoil when I go too far.

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PostPosted: Thu May 13, 2021 1:34 pm 
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When Jay gave us the Organizer’s Choice award at Sebring I made sure to tell everyone “Slant did NOT Sux!” :mrgreen:

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PostPosted: Thu May 13, 2021 8:51 pm 
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Lol! Amen Brother! Those clowns had all sorts of wrong know-it-all reasons why slants were failing. Only a lack of now-common windage & pan baffling really is missing from the Slanty's basic system. Everything else is condition/prep related.


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PostPosted: Thu May 13, 2021 8:54 pm 
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Oh, & thx for all of the detailed run-downs guys, much appreciated!


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PostPosted: Fri May 14, 2021 8:04 am 
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Yeah, we've always run with a transmission brace.

Our first cracked case started at the lower passenger-side bell housing bolt hole, or maybe the adjacent hole for the locating pin in the engine block. The lowest bolt hole should have the most static tension, from the way the engine block + transmission case assembly sits on the 3 mounts. (Think back to those beam-bending problems in engineering school.) It might also have the highest cyclic loading, but I can't really predict how the driveline vibrations excite stresses in the bolted case assembly. It's also possible that our crack was initially caused by a misalignment of the engine block locating pin while doing an engine swap (the monkeys make mistakes when they get tired), but that's just a guess on my part.

The current crack has me baffled. I think it's coming from a front-driver's side pan bolt hole, but we'll have to get the transmission out of the car to confirm. This area should still be in tension since it's near the bottom of a "beam" that's supported on both ends, but my gut says there would need to be either excessive cyclic stress or a material defect to start a crack here.

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PostPosted: Tue May 03, 2022 11:00 am 
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Now that ToadRacer has been through three races with something to report, I'll add my little piece here...

ToadRacer 1 engine was a take-out I bought many years ago and just let sit with its 904. We put it in ToadRacer and just added a four barrel & headers.
It ran like a top for the race at Sebring with no issues.

ToadRacer 1.5 was just TR1 with a slightly better head (mild porting, same valves & chamber size).
It still ran fine for the NCM race. It maybe had a little more pep to its step... It is now a good back up engine.

ToadRacer 2 engine is a Perfessor Lou build with a purdy head & cam, bored, etc.
It was runnin' like a scalded monkey at CMP... Until that dreaded air cleaner bolt snuck up on us again! Luckily we caught it before it did catastrophic damage. It ate up the tops of #1 and #6 pistons and dimpled up those chambers a bit. We put one new intake valve in #1 to be safe and put it back together. It sounds okay and we plan to run it as is at the upcoming NCM race in September. We didn't get to test it after we put it back together because the 7 1/4 gave up about that same time. More to follow on this one...

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PostPosted: Tue May 03, 2022 2:08 pm 
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I suggest that you invest in a 10 cent cotter pin and drill a hole in that stud and pin that nut fast! :D :D

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