cylinder crack - anybody?

**M2cupcar** · 7-31-06, 9:15

And here I was just thinking I had a head gasket problem.

Actually, I still think I do/did, but this happened during that time. This is a 2000 Kia block that was overbored 3mm. It's got about 400 miles on it, of which maybe 5-10 were under boost, and of those most were no more than 6psi. It saw 8 psi maybe five times. I've got a full gauge set (egt, oil temp, oil press, coolant temp, knock sensor, wbO2...) and never saw anything suspicious on the gauges. There was high crankcase pressure, so I assumed that the head gasket (copper w/o embossing or o-ring) was leaking compression into the crankcase via the oil drainbacks. I did a compression check, which confirmed the head gasket problem- after 400 miles the compression numbers were the same as pre-build numbers (1=140, 2=120, 3=120, 4=180). I'd orginally assumed those numbers were results of a non-broken-in engine (rings not seated). I pulled the head Sunday morning to find the crack. Other cyldiners looked fine, and this was the only sign of failure. Piston tops are clean, cylinder walls look good. I'm willing to chalk this one up to a weak casting by Kia- unless somebody can convince me otherwise. Usually you see something else break before a cylinder wall.

Fortunately I still have my original Mazda FE3 on the engine stand, and have already started moving parts over. I just hate to lose that 339cc. I guess it will happen, just later. - rob

**shwine617** · 7-31-06, 12:52

maybe you bored it out to much for it to handle the stress under boost. Not sure what the bore limit is though.

**M2cupcar** · 7-31-06, 13:06

The sticky says 5mm for max. and 2.5mm seems to be the norm. Engine builder/machinist said max. safe overborre for boost was 3mm based on remaining cylinder wall thickness. That said- any overbore may have been too much for this kia block. You never know 'til you try.

**Dutch** · 7-31-06, 13:19

thanks for trying and sharing

**M2cupcar** · 7-31-06, 13:32

I still think it's do-able. I just think I used a crap block. I will look at it eventually to see what it looks like on the "inside". But the next 3mm overbore will me on a genuine mazda block... providing the piston is ok, which it looks like it is.

**anarchyx34** · 7-31-06, 14:46

Why even overbore at all?

**M2cupcar** · 7-31-06, 14:56

to fit the biggest mazda 4 cylinder possible in a Miata, and then stick a turbo on it

**anarchyx34** · 7-31-06, 18:02

Yeah but how much more diplacement can you get with a 3mm overbore? .1 liters? Dosent sound worth the trouble to me.

**M2cupcar** · 7-31-06, 18:16

.139 - no trouble- it's all the same amount of work and cost. Rather 1mm over, why not go to 3mm for the "free" displacment. I guess the real reason for the 3mm over, was the fact that forged JE 89mm (3mm over) pistons were picked up on eBay for cheap (something like $200).

**shwine617** · 7-31-06, 18:57

are you using pistons made for an fe3 or are they for a dsm or something?

**M2cupcar** · 7-31-06, 20:22

chevy cosworth vega- this guy had a vega he raced and had this custom made from JE but never installed them.

**fredio54** · 7-31-06, 21:25

i'm sorry to hear about your crack. it would be somewhat ironic to all of the "randys page" following mx6 public if it was a bad idea to bore that much.

looking at the other side of the bores, its apparent that there is only about 5mm of meat there, and also that it is porous and rough cast on the surface(and therefore of variable thickness). i still would've thought you'd get 1.5 out of each side without issue though. i guess you and randy just got unlucky on that particular block. and him on the one before it too. better luck with the next one :-)

what did/does randy do for a living anyway? it was alluded to but never mentioned.

i've always been curious.

fred.

**M2cupcar** · 8-1-06, 12:03

That's the risk with doing something first. I knew that. It's only painful when the parts you haven't modified or manipulated fail for no apparent reason.

Oh- and this is Randy's block. I was going to stick an untouched Mazda FE3 in and when this came up for sale- I figured why not. Same amount of work- just more motor. And most of the Mx5 oriented stuff was sorted out.

The decision for the overbore amount was ok'd by his engine builder based on cylinder wall thickness. That said, I would have probably gone with the (my) engine builder's recommendation also. Once it's disassembled, I'll check out the casting on the coolant side. Hopefully I'll find a bad spot- otherwise I'll be using smaller pistons for a 2.2. I'll also get the builder that put together my last race motor to look at it- he's good. Either way I'll update this thread with results for others. Maybe it'll reveal some QC issues with Kia castings? I know the previous Kia block he was using had a crack in the casting on a coolant path.

I think he's something like a internet commerce consultant for corporations. He's just a BIG mazda geek as a hobby.
- rob

**SixSick6** · 8-4-07, 2:15

Is that between 2 and 3 or 1 and 2 or 3 and 4? If the block is anything like the F2 then it isn't suprising to see that being that there is a difference in wall thickness between 1 and 2 and 2 and 3 and 3 and 4.

RobbieRat · 8-4-07, 18:14

No thats a damn shame, i wonder if the Kia block has anything to do with it, what sort of side clearance are u running on it?

7-31-06, 9:15	#1 (permalink)
M2cupcar Join Date: Jun 2003 Location: Atlanta, GA, USA iTrader: (1)	cylinder crack - anybody? And here I was just thinking I had a head gasket problem. Actually, I still think I do/did, but this happened during that time. This is a 2000 Kia block that was overbored 3mm. It's got about 400 miles on it, of which maybe 5-10 were under boost, and of those most were no more than 6psi. It saw 8 psi maybe five times. I've got a full gauge set (egt, oil temp, oil press, coolant temp, knock sensor, wbO2...) and never saw anything suspicious on the gauges. There was high crankcase pressure, so I assumed that the head gasket (copper w/o embossing or o-ring) was leaking compression into the crankcase via the oil drainbacks. I did a compression check, which confirmed the head gasket problem- after 400 miles the compression numbers were the same as pre-build numbers (1=140, 2=120, 3=120, 4=180). I'd orginally assumed those numbers were results of a non-broken-in engine (rings not seated). I pulled the head Sunday morning to find the crack. Other cyldiners looked fine, and this was the only sign of failure. Piston tops are clean, cylinder walls look good. I'm willing to chalk this one up to a weak casting by Kia- unless somebody can convince me otherwise. Usually you see something else break before a cylinder wall. Fortunately I still have my original Mazda FE3 on the engine stand, and have already started moving parts over. I just hate to lose that 339cc. I guess it will happen, just later. - rob

7-31-06, 12:52	#2 (permalink)
shwine617 Join Date: Aug 2004 Location: Spotswood, NJ, USA Age: 23 iTrader: (0)	maybe you bored it out to much for it to handle the stress under boost. Not sure what the bore limit is though.
	90 MX6 GT http://www.cardomain.com/ride/2036393 Stock: 15.446 @ 88.78 F2T Best: 12.71 @ 104 FE3T: 11.941 @ 99.03 (missed 4th) 470 WHP Turbonetics 50 trim @ 30psi videos:http://videos.streetfire.net/uploaded/Shwine617.htm

7-31-06, 14:46	#6 (permalink)
anarchyx34 Experiment 626 Join Date: Sep 2000 Location: Staten Island, NY Age: 31 iTrader: (0)	Why even overbore at all?
	Anarchyx '98 VW Jetta K2- Daily driver. '94 Miata C-package- Tein S-tech, Tokico Illumina, FCM bump stops & 15" OZ Superleggera, MSPNP

7-31-06, 18:02	#8 (permalink)
anarchyx34 Experiment 626 Join Date: Sep 2000 Location: Staten Island, NY Age: 31 iTrader: (0)	Yeah but how much more diplacement can you get with a 3mm overbore? .1 liters? Dosent sound worth the trouble to me.
	Anarchyx '98 VW Jetta K2- Daily driver. '94 Miata C-package- Tein S-tech, Tokico Illumina, FCM bump stops & 15" OZ Superleggera, MSPNP

7-31-06, 18:57	#10 (permalink)
shwine617 Join Date: Aug 2004 Location: Spotswood, NJ, USA Age: 23 iTrader: (0)	are you using pistons made for an fe3 or are they for a dsm or something?
	90 MX6 GT http://www.cardomain.com/ride/2036393 Stock: 15.446 @ 88.78 F2T Best: 12.71 @ 104 FE3T: 11.941 @ 99.03 (missed 4th) 470 WHP Turbonetics 50 trim @ 30psi videos:http://videos.streetfire.net/uploaded/Shwine617.htm

7-31-06, 13:06	#3 (permalink)
M2cupcar Join Date: Jun 2003 Location: Atlanta, GA, USA iTrader: (1)	The sticky says 5mm for max. and 2.5mm seems to be the norm. Engine builder/machinist said max. safe overborre for boost was 3mm based on remaining cylinder wall thickness. That said- any overbore may have been too much for this kia block. You never know 'til you try.

7-31-06, 13:32	#5 (permalink)
M2cupcar Join Date: Jun 2003 Location: Atlanta, GA, USA iTrader: (1)	I still think it's do-able. I just think I used a crap block. I will look at it eventually to see what it looks like on the "inside". But the next 3mm overbore will me on a genuine mazda block... providing the piston is ok, which it looks like it is.

7-31-06, 14:56	#7 (permalink)
M2cupcar Join Date: Jun 2003 Location: Atlanta, GA, USA iTrader: (1)	to fit the biggest mazda 4 cylinder possible in a Miata, and then stick a turbo on it

7-31-06, 18:16	#9 (permalink)
M2cupcar Join Date: Jun 2003 Location: Atlanta, GA, USA iTrader: (1)	.139 - no trouble- it's all the same amount of work and cost. Rather 1mm over, why not go to 3mm for the "free" displacment. I guess the real reason for the 3mm over, was the fact that forged JE 89mm (3mm over) pistons were picked up on eBay for cheap (something like $200).

7-31-06, 20:22	#11 (permalink)
M2cupcar Join Date: Jun 2003 Location: Atlanta, GA, USA iTrader: (1)	chevy cosworth vega- this guy had a vega he raced and had this custom made from JE but never installed them.

7-31-06, 21:25	#12 (permalink)
fredio54 Join Date: Aug 2004 Location: Auckland, New Zealand iTrader: (1)	i'm sorry to hear about your crack. it would be somewhat ironic to all of the "randys page" following mx6 public if it was a bad idea to bore that much. looking at the other side of the bores, its apparent that there is only about 5mm of meat there, and also that it is porous and rough cast on the surface(and therefore of variable thickness). i still would've thought you'd get 1.5 out of each side without issue though. i guess you and randy just got unlucky on that particular block. and him on the one before it too. better luck with the next one :-) what did/does randy do for a living anyway? it was alluded to but never mentioned. i've always been curious. fred.
	DIYEFI.org - TRUE DIY engine management Mazda FE3/FE-DOHC Master Index Thread (work in progress) Mazda truck with FE-DOHC/FE3 "BIG like your house" Holset Turbo drinking 2.2 litres of fuel per minute ~= 385hp crank RIP SleepCounter :-( we will miss you! - RIP fredio54 :-( will we miss you?

8-1-06, 12:03	#13 (permalink)
M2cupcar Join Date: Jun 2003 Location: Atlanta, GA, USA iTrader: (1)	That's the risk with doing something first. I knew that. It's only painful when the parts you haven't modified or manipulated fail for no apparent reason. Oh- and this is Randy's block. I was going to stick an untouched Mazda FE3 in and when this came up for sale- I figured why not. Same amount of work- just more motor. And most of the Mx5 oriented stuff was sorted out. The decision for the overbore amount was ok'd by his engine builder based on cylinder wall thickness. That said, I would have probably gone with the (my) engine builder's recommendation also. Once it's disassembled, I'll check out the casting on the coolant side. Hopefully I'll find a bad spot- otherwise I'll be using smaller pistons for a 2.2. I'll also get the builder that put together my last race motor to look at it- he's good. Either way I'll update this thread with results for others. Maybe it'll reveal some QC issues with Kia castings? I know the previous Kia block he was using had a crack in the casting on a coolant path. I think he's something like a internet commerce consultant for corporations. He's just a BIG mazda geek as a hobby. - rob

8-4-07, 2:15	#14 (permalink)
SixSick6 Join Date: Sep 2001 Location: San Diego, CA, USA Age: 32 iTrader: (2)	Is that between 2 and 3 or 1 and 2 or 3 and 4? If the block is anything like the F2 then it isn't suprising to see that being that there is a difference in wall thickness between 1 and 2 and 2 and 3 and 3 and 4.

8-4-07, 18:14	#15 (permalink)
RobbieRat Join Date: Oct 2005 Location: , Melbourne Age: 43 iTrader: (0)	No thats a damn shame, i wonder if the Kia block has anything to do with it, what sort of side clearance are u running on it?