View Full Version : Cracked piston-small cracks in block-now what
:confused: The truck (1994 one ton /250,000 miles) ran perfect and was never overheated when all at once smoke came from around the dip stick and the engine ran a little rough. I pulled the engine and found that the third piston back on the oassenger side (#6 piston ?) was cracked across the top. Also the block has two cracks up along the main bearing bolts on either side of the cracked piston. One crack is about 1/2 inch upward from the main bearing cap and the other is about 3/4 inch up from the main bearing cap. Both run straight along the bolt. Now what? Is this block worth using or repairing? Ive read in the forum where many people have a cracked block problem and have to scrap out the block. Are these type of cracks what they are talking about? How serious are these cracks? what do I need to do next? How come the two block cracks are on both sides of the cracked piston? Thanks in advance for any help.
The cracked piston is an easy fix (replace) The cracks in the main webs are pretty much an end of the road for the block.
I hate to be the harbinger of bad news but once these cracks appear they dont go away and they will continue to progress until there is a catastrophic failure of the engine.
You can salvage most all the rest of the parts though.
The center main webs are the place these blocks crack. It was just bad luck and probably had nothing to do with the piston.
Cracked pistons can be the result of a bad injector that is causing an overheat situation on the piston crown.
Robyn
Too much coincidence for me, especially on a 94 model year. Sounds like maybe hydroloc from a sudden head gasket failure on that cylinder cracked the piston & block at same time. Either way, its over for the block. New, reman or used engine only options now, unless you can locate a block. Sorry about your bad luck.
Well the news you gave me wasn't exactly what I wanted to hear but I guess I did ask for it. Do the cracks in the block always start at the main cap bolt hole and work their way up? What happens next with the crack? Does it travel upward and break into the water jacket somehow or is the ultimate failure caused by the main bearing cap pulling loose from the block? Is there any way to repair these cracks as they are only 1/2 -3/4 long and follow the bolt threads? I'm not going to invest time and money (I don't have much money) into the block if it's destine to fail but could a person drill relief holes at the end of the cracks or pin the cracks I would give it a shot. What about the girdle reinforcement supports I have heard people talk about in the forum? If I am going to look at a used engine how do I know the block condition? I had driven this truck on a round trip of 90 miles the night before and it ran absolutely perfect. I even commented how great it ran (probably my mistake). My wife took it to work the next day (9 miles) with no problem. When she started it up to come home she said it started running rough at startup. My point is that if I was looking for another engine and it ran as great as mine did the day before, I would just be buying another bad engine. What can a guy do when he buys a used engine? If I buy a block I can at least look it over but can you see hairline cracks without having the block magnifluxed? Sorry for the lengthy response.
The best way to see cracks is magnafluxing, but if they're evident without that, the block is toast; when considering a new block magnafluxing/certification is well worth the cost. Forget stop drilling - the damage has already begun, and stress relief isn't going to stop the inevitable. Bolt that thing back together with a new piston or two, and the outcome will be destruction of reuseable parts. It's time for major surgery...sorry...
A used engine is always a crapshoot - it could be just fine, or someone may have overheated it, etc., etc., etc. However, if budget constraints prevent a rebuilt short block (Jasper), a used engine may not be all that bad if sourced from a wreck.
I guess you guys are right about giving up on the cracked block. It was a good engine that ran great and that looked to be in great shape when I tore it down (except for the cracks). Anyway, I've passed the denial stage and need to move on. I don't want to go the used engine route as I would have no idea of its condition. I need a truck that I can trust to travel with. I will try to locate a good block but i'm not sure how easy that will be. It seems that finding a good rebuild would be the safest (though most expensive) way to go. How do I find a supplier of good rebuilt engines? Do places like Autozone or Orielly's have engines that have good blocks? Also I understand that some pistons are great while others seem to fail. I see on the forum that some block #s are better blocks than others? (the cracked block is a 929 block). I need some help to get me thriugh this. Thanks for any input.
I would go with Jasper if price is a consideration for a rebuild.
Better would be a rebuild from one of TDP's fine sponsor shops.
If you want to make a drive down to north Florida, I have a short-short 599 block takeout that needs cylinder resurfacing (light scoring on 5 through 8), includes Kennedy dual thermostat/130 GPH water pump, good turbo, etc...cheap...PM me for more.
For the money if you are going to buy an engine and want something reliable I would not get a rebuild but go with the new GEP block. Places such as Peninsular Diesel has had great reviews from those on this page, and have been great when I have e-mailed them with questions; Ron Schoolcraft (uses all of the upgrades from JKs site). I have a Reviva engine in my truck that also uses the GEP block, however they require an "authorized mechanic" to install it adding to the overall price - I didn't have the time or space to do mine at the time so shelled out the $$ instead. No matter how you look at it, this is going to cost a good bit of $ and I would go with a new engine to put that time and $ into. Just my $0.02
I agree - I reengined my motorhome with an uprated Peninsular/AMG engine built to spec, and have been delighted. The only issue was a failed turbo, which Peninsular got on right away.
I want to thank everyone for your input. You guys have discussed exactly what has been on my mind and have cleared up a lot of things. I've went from having a great running truck -- to having to overhaul my existing engine -- to having to find another block that I can trust -- to going with a used engine which is also a gamble -- to going with a rebuilt engine (with a used block) -- to buying an engine with a new block. If I went with a reman (Jasper or others) I'm afread I would always be worried about the block. It seems that a new block even though more expensive would be the way to go. I intend to keep the truck for a long time and peace of mind means a lot. I will spend some time today trying to find out more about the GEP/AMG engines. This is all new to me. If anybody can direct me to web sites I would appreciate it. I am going now to check on TDP for info. Thanks again everbody for the valuable input.
Why not go directly to the source http://www.amgeneral.com/vehicles_gep.php or http://www.optimizer6500.com/ to find out info. If you click on the contact link you can e-mail GEP directly, they were very helpful when I contacted them. I would also talk to the folks at Peninsular they are linked in the advertiser section.
Try this www.peninsularengine.com
That's where I got my engine, and I've been very satisfied - but be aware, they can be a bit slow on fulfilling the commitments. Nevertheless, I'd not hesitate to deal with them again.
Thanks for the web site information. When I tried the Peninsular website link yesterday from TDP advertisers all I got was a site under construction notice. When I tried to link from Rustyk's hyperlink to Peninsular I wound up at a meet sexy women web site. Maybe I wasn't meant to buy my engine from them. Next I'm going to check out the two sites bl78ljb provided. I think I'm headed down the right track with a AMG/GEP engine. I think for this truck that this is the best way to go. I'll keep you guys posted
93GMCSierra
01-13-2008, 18:17
rusty's got one too many http://'s in there. if you copy and paste without the extra you get them.
I just visited the AMG/ GEP websites. Can a person buy directly from them or do I need to still go through Peninsular or others? I thought I saw somewhere in TDP forum that Peninsular was the only outlet for these engines and that you couldn't buy directly from the factory. I didn't see anything on the websites to indicate one way or the other. I can give them a call tomorrow to find out
You need to buy the GEP engine from a reseller such as Peninsular. Try this link http://www.peninsularengine.com/ or e-mail at mattk@voyager.net (matt@voyager.net).
When I tried to link from Rustyk's hyperlink to Peninsular I wound up at a meet sexy women web site.
NOW, I'm really disappointed, because all I got from trying my posted link was Peninsular Engines...whatever happened to the site with the sexy women??? :D
Rustyk Maybe it was just wishful thinking on my part. Or maybe I should spend my 6.5 engine money on getting my computer repaired instead. I always thought my computer had a mind of its own. BTW, I contacted Peninsular but haven't heard back from them.:cool:
Rob4, I sent you a PM with the Secret Decoder Ring email for Peninsular...post here if you don't get.
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