Cracked cylinder walls?

Mike T

Well-Known Member
Joined
May 3, 2013
Tore a used motor down today that ran good on the stand but appears to have cracks in the cylinder walls of 4 & 6.
Was told motor had bad HG's but actually they were factory originals in very good shape. All of the cylinders have varying degrees of water damage so something weird has happened to it in the past. Did a search and cracked cylinder walls don't seem to be all that common. May not be cracks but i'm about 90% sure.


Any thoughts?

cracks marked.png
 
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I found it at tear down. Engine was drinking coolant from a cracked intake port. The cracked cylinder bore in the same hole was just a bonus.
 
This one would start to overheat after about 10 minutes on the stand at about 2500 rpm. That was the only sign, the oil was clean and the radiator hoses only got tight just before temps went up.
 
I had a .030 over block that cracked a cylinder. Sleeved it and shortly thereafter it cracked a different cylinder...but all the way to the top of the block. Tossed the block and kept the rotating assembly. Found another STD bore block...and will eventually have it bored for the .030 over rotating assembly.
 
I guess lucky for you that TA is only a few weeks away from getting their new blocks in? :D

That's great that they are back, one of our local club members tried but could not get one about 6 months ago.



Are those valve reliefs on the pistons? What is the bore ?

Yes, it's a standard bore N/A motor that I'm converting.....well maybe I'm still not certain that it's cracked yet.



I had a .030 over block that cracked a cylinder. Sleeved it and shortly thereafter it cracked a different cylinder...but all the way to the top of the block. Tossed the block and kept the rotating assembly. Found another STD bore block...and will eventually have it bored for the .030 over rotating assembly.


Do you know what caused it to crack?
 
Several things can contribute to cylinders cracking. The closer you bore to the water jackets...the thinner the cylinder wall becomes. A million heating/cooling cycles since 1987. Pressurizing the cylinders under boost...expansion and contraction. I'm sure there are others as well. I currently run a standard bore. ET/MPH and build are in my sig.
 
Is a sleeved block just as good as nonsleeved ? I ask because I have a block that has a ding in the wall when a valve broke off and rattled around . It's really not to bad but I don't think it would come out with .010" over bore .
 
Really can't say for sure that they are cracked. Looking at them you would swear that their cracked but I'm started to have doubts after a little honing. The pictures aren't the best representation of what I'm seeing.
 
Is a sleeved block just as good as nonsleeved ?
Yes they can be, as long as its done correctly. My sleeved 109 has run mid 10's. I just went through it again recently, made some changes and have it up and running again.
 
Really can't say for sure that they are cracked. Looking at them you would swear that their cracked but I'm started to have doubts after a little honing. The pictures aren't the best representation of what I'm seeing.
Honing it will prob hide the crack rather than reveal it. Safe thing would be magneflux check it at a machine shop.
 
Honing it will prob hide the crack rather than reveal it. Safe thing would be magneflux check it at a machine shop.

Yes your right. They also sell test kits that use a series of spray on dyes but I bet that would show scratches and gouges as being cracks too.





Could be a thin spot in the casting. Here's a cheap wall thickness ultrasonic meter.
http://www.idiytools.com/wholesale/gm100-ultrasonic-wall-thickness-gauge-meter-tester.html
Might be worth a shot.


Nice little tool, I could use that for a lot of stuff around the shop. You could be on to something with the casting because there are two horizontal marks in the #6 that line up perfectly with a step in the casting that can be seen through a water jacket.

It'll suck if it's junk because that little ring ridge in the picture is almost gone with a .001 (standard bore) hone and it only shows .0015 taper.
 
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