jeffer949 Posted March 3, 2008 Share Posted March 3, 2008 i blew a head gasket this afternoon and my head off and found the bridge between 4 and 5 blown which i expected then i started looking closer at the cylinders and was looking at number five and i found this!! well im pretty screwed and looks like i have to pull the whole engine. and look for some over bore pistions. and im gonna have to rebuild the whole thing... so looks like im not going to dni... man this sucks!!! Quote Link to comment Share on other sites More sharing options...
Tony D Posted March 3, 2008 Share Posted March 3, 2008 WELCOME TO THE CLUB! Our Bonneville engine did that with pressed-in pins, and our damage was 0.080" scores down all six bores. Makes you think a second time about teflon buttons in an OEM rebuild.... Quote Link to comment Share on other sites More sharing options...
Warren Posted March 3, 2008 Share Posted March 3, 2008 That bites...anything I can do to help, lemme know. Quote Link to comment Share on other sites More sharing options...
jeffer949 Posted March 3, 2008 Author Share Posted March 3, 2008 all ready on the building plans i dont get why people dont use them. they are so cheap and so functional. i used to throw them into all the 4stroke dirtbikes i used to build for customers just as precautions and those have circlips. dont know how many times i had one of those come out!!! Quote Link to comment Share on other sites More sharing options...
jeffer949 Posted March 3, 2008 Author Share Posted March 3, 2008 not sure there is much anybody could do lol. doing the work isnt a problem its the funds behind it. if i had the money i could rebuild it faster than i could get parts. but i dont... Quote Link to comment Share on other sites More sharing options...
jeffer949 Posted March 3, 2008 Author Share Posted March 3, 2008 what do you guys think about throwing my p90 on my old 260 block? it did burn a little oil on first start up but it wasnt horrible.... Quote Link to comment Share on other sites More sharing options...
cholag Posted March 3, 2008 Share Posted March 3, 2008 While you guys are on the subject of pistons and pistons pins I have a question. I am at the point of my 1983 280zxt engine build where I am saving for my forged pistons because I will be running 15-20 pounds of inter cooled boost. So my question is when I get my forged pistons should I have them made with free floating pins and tell them that the rods will be modified for free floating pins. Or should i be alright with pressed in pins? Quote Link to comment Share on other sites More sharing options...
jeffer949 Posted March 3, 2008 Author Share Posted March 3, 2008 why do you need forged pistions for 15-20lbs of boost?? big phil is at like 26 ish psi on stock internals.. i was running 15ish on this motor and the pistons are fine Quote Link to comment Share on other sites More sharing options...
Tony D Posted March 3, 2008 Share Posted March 3, 2008 i was running 15ish on this motor and the pistons are fine By no means am I trying to rub salt in the wounds, but I would be remiss not to point out the obvious and say: 'your photos would indicate otherwise' The choice of full floater and pressed in is (IMO) a matter of how often you plan of pulling down the engine for refreshing. People were shocked we did not use Full Floaters in our Bonneville Engine...but why? We ran four seasons on the engine before something made the piston pins work out and kiss the walls. Obviously we didn't pull it down after every meet (hell, or every season for that matter!) and missed something that should have indicated pin movement. But unless you are pulling the thing down all the time, what advantage do you have on full floaters? And with small teflon buttons on stock pins if something DOES happen, at least you can save your cylinder bore till you DO get it apart. The L20A does have teflon pin buttons on Pressed-In pins. 9500 rpms. Stock Rods. Chances are good (again IMO) that we wasted money on the pin buttons on this engine. I don't see pins scoring the walls. I see catastrophic failure and spectacular engine damage from something snapping at that rpm level. But the L28 was only 8500, and that's really an enduro setup by comparison. Some pin buttons and pressed in pins means you have to go see the machinist to change pistons. Full floater, pull some circlips or spiralocks and you got a new slug on your rod. Nice for a quick refresh during the week in between races. As long as everything ie weight matched! Quote Link to comment Share on other sites More sharing options...
blueovalz Posted March 3, 2008 Share Posted March 3, 2008 Question: Why does the wear pattern extend all the way up to the ring ridge? I'm wondering why the pin wear doesn't stop much lower below the ring ridge. Quote Link to comment Share on other sites More sharing options...
OlderThanMe Posted March 3, 2008 Share Posted March 3, 2008 Yeah it is like you broke a ring and not your wrist pins. Detonation? Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted March 3, 2008 Share Posted March 3, 2008 I don't think it's wrist pin scoring either. It's doesn't line up with the bore centerlines in the photo. That cylinder is apparently cleaner than the others also. That could be from coolant leak or running HOT and lean which could also have been detonation. Measure up that score with a bore gauge. You might be able to run it like that or just change out a piston and do a manual hone as a temporary fix. Quote Link to comment Share on other sites More sharing options...
big-phil Posted March 3, 2008 Share Posted March 3, 2008 please don't happen to me please don't happen to me please don't happen to me please don't happen to me please don't happen to me please don't happen to me please don't happen to me:icon29: Quote Link to comment Share on other sites More sharing options...
1 fast z Posted March 3, 2008 Share Posted March 3, 2008 With double true arc rings, it would not have happened. Tony, what did cause the .0035" interference fit to walk? Quote Link to comment Share on other sites More sharing options...
jeffer949 Posted March 3, 2008 Author Share Posted March 3, 2008 now that i look at it and arent in huff puff over it your probably right. i can barely feel it with my finger nail also. i do have an old set of dished pistions form a l28 that could prolly throw in with new rings and a hone job.. maybe some new bearings... ugggh any budy know where to get a pretty good ring set for decently cheap? Quote Link to comment Share on other sites More sharing options...
jeffer949 Posted March 3, 2008 Author Share Posted March 3, 2008 oh and it was cleaner because i had wiped it out with a rag it did look like the rest of the pistons Quote Link to comment Share on other sites More sharing options...
Administrators BRAAP Posted March 3, 2008 Administrators Share Posted March 3, 2008 ... man this sucks!!! Yeah that does suck for sure. Sorry to see that. I realize this doesn’t matter as the short lock needs to be torn down and rebuilt regardless, I just want point out what that scuffing really is, it is not your wrist pin. 1) Not how the scuff is wide! The wrist pin would leave two narrow gauges in the cylinder wall from the sided of the wrist pin contacting the cylinder wall. 2) Also note that scrape is offset, i.e. not in the same plane as the wrist pin. If looking straight down on the block, standing on the passenger side of the engines, that gouge is closer to the 10:00 position. Wrist pin would gouge the 9:00 position. 3) Also note, that gouge comes up as high as the top ring! Writ pin much lower in the piston. What happened in that cylinder is the top ring expanded to the point the ends butted up together and the ring was “seizing†in the cylinder, yet the piston was still dragging it up and down cylinder causing that scoring. Depending on many how tight that ring was during this, could also break or crack the ring lands on the piston. Yours looks to be pretty mild, pistons “might†be ok, though if you are considering reusing those pistons, they need to be scrutinized “very†carefully. What causes this situation is too much combustion chamber heat, (abnormal combustion which is most likely the cause here hence the blown head gasket), or inadequate cylinder cooling, or ring end gaps too close for the intended application, or any combination of the above. Depending on how long that excess combustion temp was taking place, the piston itself may have also expanded to the point it contacted the cylinder wall. Generally around the wrist pin region of the pistons is where you will see piston scuffing from that situation. For boosted engines, ring end gaps must be a wider due to higher cylinder temps. N/A ring end gaps will due this in a boosted application. As the ring heats up, it expands, you want that gap to be as tight as possible while in operation to minimize blow by, but not to butt together, as this will be the result. Always follow the ring manufactures ring end gap recommendations for the pistons you are using. Again, at this point it really doesn’t matter a whole lot as the short block needs to come down regardless. Just wanted point out what those scuff marks were really caused from. Quote Link to comment Share on other sites More sharing options...
Administrators BRAAP Posted March 3, 2008 Administrators Share Posted March 3, 2008 In looking closer, as OTM mentioned, that scuffing could be caused by a broken top ring… At any rate, hope you are able to get it back up and running soon. Take care, Paul Quote Link to comment Share on other sites More sharing options...
cholag Posted March 3, 2008 Share Posted March 3, 2008 Well one more question now, so if I just tune the motor real well I would be safe running 15-20 pounds of boost on stock internals? Quote Link to comment Share on other sites More sharing options...
JSM Posted March 3, 2008 Share Posted March 3, 2008 Well one more question now, so if I just tune the motor real well I would be safe running 15-20 pounds of boost on stock internals? From other posts I've researched on yes. Quote Link to comment Share on other sites More sharing options...
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