O.S. Speed T-1204, cracks at the base / mounting point

[Pontus]

Hi!
First post!

I have a, for me, weird problem with my engines. They suddenly keep breaking at the base where the screws are, leaving a big hole in the side.

Here's how they look:

[https://ibb.co/ZJHBWt3]
(A bit dirty, since they spit all nitro out all over the car...)

When it happend the first time I saw one of the screws holding it in place was loose. I thought I made a mistake mounting it, and that it cracked when I hit a curb too hard. So I took it apart and checked everything. Piston and sleeve looked fine to me (almost brand new, run about 2-3 liters since break-in), so I put them in another crankcase that was supposed to be broken in later. It ran great for a whole day on the track. The next time it ran like normal for 1 lap. When I looked at it a bit closer I saw that this also had broken in the exact same way.
If it happens once because of a mounting mistake, fine. Shame on me. But when it happens twice in the exact same way I think it's time to seek guidance!

What can be the problem here? For me there's no logic behind the way they've broken. Here's what's been running around my mind this whole weekend:

1. My first thought was that I have done something wrong during break-in. But I didn't do anything different than I've always done. And if the con rod would have been damaged, it would be more logical that the engine would break immediatly when started after being put in a new crankcase. Or am I wrong here?
2. The car is an Xray NT1 2013, and I run quite big spurs/pinions (60/17 + 54/23). Could that have something to do with it? That the engine is mounted too much "twisted", for lack of a better word, putting too much of a strain on the screws and engine mount?
3. When cleaning the car I saw that the "stiffener" (part number 336180) that runs over the flywheel has fallen off. Could this be the problem? That the chassi flex too much right where the engine is mounted, tearing it apart?
4. Did I use too much oil when putting the engine back together, making the preassure too big between the crankshaft and case, and therefore causing this? Is that even possible? Wouldn't that even out by itself when running a few laps?

One of the engines, well the crankcase, is from 2021, the other one is from 2023.
I always keep everything clean and well oiled and maintained before and after racing, and there's no rust what so ever.

I'm lost here and any help would be greatly appreciated!

 

[fstnd]

WOW. never had that happen to me. Do you happen to fly them 2 yards long and land on the cooling head? That's the only time I saw something like that happen, of course it was Kevin Talbot.
Welcome

 

[WickedFog]

If I had to guess, it's #3. That brace is obviously there for a reason. Without seeing the car with the engine in it, I can't say for sure. But without the brace, what is the next thing keeping the chsssis from flexing there? Is it the spur gear? Look it over and see how a load could be getting to the engine case and causing it to break. Pics might help us help you.

Welcome to RCT!

 

[TMAXX]

Just a guess but make sure the case isnt bottoming out and when tightening your pulling the ears down a bit. Then the vibration is finishing it off.

I havnt seen any with that bottom rib but the way that its shiny looks like rubbage to me

 

[Pontus]

Thank you all for the quick replies!
So I can rule out that the con rod is "bent" or something internal with the engine is the cause?

@fstnd I never "jump it" intentionally other than hitting a curb to hard and flying a bit. I'm a track driver. But even in my worst crashes I've never sent it like Mr. Talbot

@TMAXX Hmm, haven't thought of that! Definitely need to check that out! I use another mount than last year (monoblock, part number 338713) so that part is new to the setup.

@WickedFog I would say that the next thing keeping it from flexing at that area is the engine mount. But it's a solid 1-piece mount, so there shouldn't be room for enough flex to rip it apart.
Here's a few more pics! The first one is of my "rain car". It's the exact same car but built of replaced spare parts of the other one, and with a cheaper engine. But you can see the brace. The other two images show the same area of the main race car, with the brace missing:

 

[Littlemotor]

If your engine-to-mount screws aren’t backing off, then that’s a casting defect in the block (considering it’s a one piece mount, and produced by Xray). Man-I hate it for ya.. As much as people brag on OS, and hate on anything that’s not-I highly doubt they’ll do anything for ya.. That’s just crazy.. Absolutely a defect in a run of engine blocks imo. I actually work in a forge/foundry as an Industrial Maintenance technician fwiw.. I’d DEFINITELY give OS a call regardless, and see what they can do for you. Good luck.

 

[Pontus]

@Littlemotor Yeah, it sucks... I've sent an email to OS with the same information and images from this thread. I'll report back when/if they answer! Whatever they say this has still ruined my season

It's still weird that they suddenly break. The age differ by 2 years, so they should be from different production runs... I haven't had time to check if the engine bottoms out against the chassi. That would explain it! But then it's the Xray mount that's the cause... And that sounds unlikely to me!