byrd auto Posted July 28, 2014 Share Posted July 28, 2014 (edited) Hey guys I am having serious problems with an engine. I did a complete rebuild last year after finding both heads cracked and all 6 liners cracked. I installed all new liners and new heads. Made approximately 6 loads with the truck last year and this year made two and it started blowing water from the coolant tank. Upon removing the heads I again found 2,3,4,5 cylinders with cracks. The cracks are not up and down. They are side ways in the liners. I need help to determine what could be causing this. Thanks for any input.. Edited July 28, 2014 by byrd auto Quote Link to comment Share on other sites More sharing options...
wheeler73 Posted July 29, 2014 Share Posted July 29, 2014 Where are the cracks located in the liners. If they are where the line meets the counter bore and just above that area I have seen too much silicone used to seal the counter bore cause the cracked line. Have seen a couple trash the block because of too much silicone. All it takes is a very samll bead of silicone. Quote Link to comment Share on other sites More sharing options...
byrd auto Posted July 29, 2014 Author Share Posted July 29, 2014 cracks are about mid ways down and located on the side toward the rear of the block. Quote Link to comment Share on other sites More sharing options...
wheeler73 Posted July 29, 2014 Share Posted July 29, 2014 Did you use a lot of silicone on the counter bores? Also were there any broken rings. Also when you pulled the old liners out was there a lot of silicone? If so the block might be trashed. Quote Link to comment Share on other sites More sharing options...
byrd auto Posted July 29, 2014 Author Share Posted July 29, 2014 Used a small bead of silicone when assembling the engine. I had no problem pressing the liners in and they were all flush with the block. I haven't removed the liners yet but will do so tomorrow. With this happening before it kinda throwing a red flag. I've built many engines and this is the first one I've ever seen with liners crack side ways. I've seen them cracked up and down because of scoring or heat but this is new to me. My first thought was maybe the owner or one of his employees used ether on it, locked it up, and kept trying to start it. But, that was when I thought only 3 and 4 were cracked. Being that they are companion cylinders and cracked in almost the same exact location. To much pressure in the cylinders was in my mind but I'm not sure. By the way thanks for your help... Quote Link to comment Share on other sites More sharing options...
gearhead204 Posted July 29, 2014 Share Posted July 29, 2014 it almost sounds like a miss machined block with the lower counter bores not cut square to the deck , might be time for a short block 1 Quote Link to comment Share on other sites More sharing options...
byrd auto Posted July 29, 2014 Author Share Posted July 29, 2014 I almost come to that same conclusion.... Wow that gonna hurt!!!! Quote Link to comment Share on other sites More sharing options...
wheeler73 Posted July 30, 2014 Share Posted July 30, 2014 Did you cut the counter bores the last time? If you have a depth micrometer you can at least check the counter bore depth in 4 spots and see what the reading is. Factory is 4 inches. If they have been cut then the liners need to be shimmed. It is not too bad of a job just time consuming. Quote Link to comment Share on other sites More sharing options...
byrd auto Posted July 30, 2014 Author Share Posted July 30, 2014 Wheeler 73 I think you hit the nail on the head. I removed three of the liners today and found silicone pressed down the sides. the counter bores look fine. going back with another kit and making sure not to use but an 1/8 inch bead. Thanks... I also talked to a Mack shop in this area and with the cracks being side ways he said the same thing you did....don't know why in the world Mack would go from a seal to sealant... Quote Link to comment Share on other sites More sharing options...
wheeler73 Posted July 30, 2014 Share Posted July 30, 2014 Make sure you measure the counter bore depth and clean them and look for pitting near the edge. If there is pitting near the edge or large pits in the counter bores they will need to be cut. Quote Link to comment Share on other sites More sharing options...
wheeler73 Posted July 30, 2014 Share Posted July 30, 2014 If they look good make sure you measure the depths. If they have been cut before the liners will need to be shimed. If you have to shim them make sure you put the shims on tye liners with the thinist first if you have to use a couple of shims and then apply a thin bead of silicone to the bottom shim and then install and use hold downs on the liners for about 30 min each to set the silicone. Mack says maximum counter bore cutting is 0.040. I have gone to 0.080 a couple of times as per customer request. Try to only use 2 shims per liner as any more cause issues. Quote Link to comment Share on other sites More sharing options...
wheeler73 Posted July 30, 2014 Share Posted July 30, 2014 Fyi the MP engines use o-rings on the liners. Quote Link to comment Share on other sites More sharing options...
byrd auto Posted July 30, 2014 Author Share Posted July 30, 2014 what was the reasoning behind going to silicone in the first place Quote Link to comment Share on other sites More sharing options...
wheeler73 Posted July 31, 2014 Share Posted July 31, 2014 I have no idea but it works very well. Possibly to seal some imperfections in the counter bore and or cost. Quote Link to comment Share on other sites More sharing options...
Ironhorse Posted August 1, 2014 Share Posted August 1, 2014 We cut bore .250. Engine still fine after 400000 miles. Quote Link to comment Share on other sites More sharing options...
wheeler73 Posted August 1, 2014 Share Posted August 1, 2014 The only problem with too deep of a cut is stacking the shims. I do not like more than 2 shims. I have found if more are used it is easier for them to fall down the liner and roll when installing the liners. Quote Link to comment Share on other sites More sharing options...
byrd auto Posted August 2, 2014 Author Share Posted August 2, 2014 Ok guys, I've pulled all the liners, got a new kit and was about to install. I used a new liner just to see how it would fit into the holes. The liner will slide down into 2,3,4,5,&6 but #1 seems to be tight. Anyone know what the bore spec on the block should be? Don't want this thing to screw up again. Quote Link to comment Share on other sites More sharing options...
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