Cracked Cylinder - Theories?

Tyson Henry · Posted: Sun Sep 23, 2012 11:42 am Post subject: Cracked Cylinder - Theories?

So went out to race yesterday and didn't even get to make it through the first qualifying heat.

Went out onto the track and immediately the motor started to stumble and then died. Pushed it off the track and noticed there was liquid around the motor and on the floor pan. Got back to the pits and found a cylinder stud was broken off. Was going to just replace it so I took off the exhaust and then saw a big old crack on the cylinder. Here are some pics of the damage:

Trying to figure out what happened. Here is my possible theory, let me know if this seems likely.

So when taking off the cylinder the front right nut was pretty loose. So I was thinking that maybe since that corner was loose, the opposite corner stud broke and then when that happened the cylinder was moving around too much and then cracked on the front left.

IDK, what do you guys think? That metal plug that is on the bottom of the cylinder was sitting in the bottom end. Amazingly nothing even got marred.

Steve Buckner · Joined: 22 Apr 2003 Posts: 839

http://www.ekartingnews.com/viewtopic.php?t=79656&postdays=0&postorder=asc&start=60

Tyson Henry · Posted: Mon Sep 24, 2012 10:16 am Post subject:

Yeah, I had read that thread before. Knew about over torquing the studs. Pretty sure I didn't though. Fairly certain I under torqued.

Anyways, I think my original thought is correct. One got loose which stressed the opposite corner which broke the stud and then the front left was way over stressed and the cylinder cracked.

Expensive lesson learned. Use loctite.

Steve Buckner · Joined: 22 Apr 2003 Posts: 839

I dont think its over torquing the nuts, its about the nut not sitting flat on the cylinder. Spot facing was the cure.
I have also seen where the holes in the cases have built up a lot of debris, oil, dirt, small peace of gasket materal, and the stud wont go down to its seated position. Installed cylinder, torqued it down, and the nut was at the end of the thred on the stud. Thinking it was ok, I was not holding the cylinder down from debris in the hole. Nut would come loose.

Just something to look at.

Tyson Henry · Posted: Mon Sep 24, 2012 12:04 pm Post subject:

Ah, good call. Ill make sure the studs are seating all the way in the cases also.

Steve Buckner · Joined: 22 Apr 2003 Posts: 839

Yep, I would pull them out and use bottom tap to clean them. Blast the holes with carb cleaner or what ever you think, WATCH THE EYEBALLS, and blast with compressed air, EYES, then clean studs and loctite them down, use the double nut trick to make sure they are all the way down. Wink

Tenny Kwok · Posted: Sun Oct 21, 2012 5:20 pm Post subject: Cracked Cylinder

I had a cracked cylinder like yours. Swedetech has encountered enough cracked cylinders to offer this modification for their engines.

http://www.swedetechracing.com/parts_accessories/pictures/cr125-long-stud_548x480-117.jpg

In lieu of this modification, one of my engine builders told me to torque the cylinder base bolts lower than the factory specs. Factory = 20 ft -lb. recommendation 12 ft-lb.

joseph hollinger · Posted: Sun Oct 21, 2012 5:58 pm Post subject:

Forget about it. That old thread is from 2009. That was a lot of miles ago in the shifter and its never happened again. Torque the nuts to the spec and you should be good (although probably not with that particular cylinder).
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Oscar Aguilera · Joined: 18 Jul 2001 Posts: 1614

that mod was for modified motors....it was needed and would save the motor from the higher compression we ran...so it is old now unless you have a modded motor. that is the weakest part of the cylinder.

even with that mod the cylinder would fatigue over time and the back would crack. i had this failure on my motor.

i think if the cylinder is old and has a lot of time on it....it is subject to breakage. the compression of the motor is trying to punt off the head and cylinder on every stroke

obviously with an improperly torqued cylinder due to debris or the nut not flat ...or just not torqued correctly would also help create a failure.

so other than getting another cylinder and trying to be more careful when doing top ends.....the only concrete answer IMO that you will get.....is you need a new cylinder.

just my opinion

Chris Fosso · Joined: 01 Jan 2009 Posts: 192

water/coolant/fluid could of ingress-ed in to combustion chamber from another source (IE: head gasket ,or excessive fuel)...something like that... and then it started to or began to hydro lock...and simulated to much compression(like a mod. motor ) and broke ear on cylinder (like a mod motor does)

i would be checking all the small things....just to be sure
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Jason Berry · Advertiser Joined: 29 Dec 2001 Posts: 296

I have only seen that one time with a Stock Cylinder. It was on an engine that had a large amount of time and many years of abuse.

The person that assembled your engine, did they spot face the cylinder where the nuts sit?
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Tyson Henry · Posted: Mon Oct 22, 2012 10:49 am Post subject:

Thanks for all the replies guys, but I am fairly confident in what happened. When I installed new studs into the cases I didn't make sure they were in there sufficiently snug to keep them from vibrating loose. Expensive dumb mistake. Shocked