So I have a bbf 501 stroker with 12.5:1 compression. Had a local shop install the engine into an OT car and put 91 octane and octane boost in without telling me. It predetonated and wrecked the spark plug on one cylinder, however it also pinched the top piston ring (45% on leak down test). I'm hoping with some heat and drive time that it may come back. Anyone else have this happen and found a fix shy of pulling the motor and freshening it up? This is a picture of the plug [/URL][/IMG] Posted using the Full Custom H.A.M.B. App!
If you believe the piston landing has collapsed enough to pinch the ring causing the leakdown problem, driving is not going to cure it.....
I work for a new car dealer (won't mention who), one of our high performance models have had problems with people running them on standard petrol (91 octane) they've been detonating and blowing the ring lands off the pistons. The manufacturer said if there was a way of proving that the engine had not always been run on 98 octane they wouldn't give any warranty. low octane + high compression = not good
Pull it down and see what is damaged... if it detonated bad enough to wreck a plug and stick a ring Il bet you will find more damage... lifted top ring lands... collapsed skirts... scuffed rod bearings, maybe more. Best to catch it all now before more damage is done.
X2! Really sucks, but as ottoman stated better safe to pull apart now rather than possible massive failure by running it.
You should be able to find some different pistons to drop the compression to around 9.0:1. Hopefully it doesn't need to be re-bored if it's already .030" over.
Sucks , but I bet the problem can't fix itself, pull it down and see what's going on inside, 45% leak down is not good -is it ?
Not sure how you diagnosed and confirmed a pinched ring land with the piston still In the block , but its not going to fix itself. You are looking at a tear down and the damage will be less now than if you continue running it.
You're right I'm not 100% sure but had the thing bore scoped and that was the best verdict we could come up with.. Looks like I will be pulling an engine in a couple weekends.. Thanks for the help! Posted using the Full Custom H.A.M.B. App!
We were planning to run 110 but the guy who installed the engine put in pump gas.. Posted using the Full Custom H.A.M.B. App!
If it damaged the spark plug and some of the porcelain was broken off it could have scored the cylinder walls. Ask me how I know this.....This doesn't go away without boring the block.
Detonation didn't directly cause that plug damage. But a piece of something did and prolly went out the exhaust after knocking around the cylinder for awhile. You gotta pull the head and have a looksee. Jack E/NJ
No he didn't build it.. My stepdad and I purchased the engine from an old hot rodder that was into bbf stuff.. Long time family friend. Had it in a pickup for about 500 miles then needed to pay some unexpected bills so he parted out the pickup. We were more than ticked off at the guy believe me! As far as I can tell it looks like all of the spark plug is there but something could have fallen off on detonation.. Cylinder walls looked clean of any imperfections with the bore scope but you can only see so much with one of those.. Im a body guy and not much of an engine builder so that's why I'm looking for some advice.. Just to mention the engine right now is putting down close to 600hp and 600tq at the crank.. Posted using the Full Custom H.A.M.B. App!
>>>Just to mention the engine right now is putting down close to 600hp and 600tq at the crank.. >>> How do you know that? And was it before or after the problem? Jack E/NJ
We had the car dyno tuned and it put 495hp and 500tq to the wheels. This was after the damage.. The guy tuning the car was the one that noticed the plug and performed the leakdown test. Posted using the Full Custom H.A.M.B. App!
48... just a couple things ...All the other plugs look ok?? do any have the appearance of contact damage... check for the correct plug for that combination. Considering the pistons and cam being used, try to find out if the cam was installed "straight up" or degreed in, which can change piston-to-valve clearances.. If you stay strictly with e85, 12.5 to 1 is doable on the street..
You can almost detect a spot where the plug was hit. How does it look in person? Were the plugs changed recently to a different number? Looks like a projected nose to me. You could put some clay on another plug, turn the engine over and check clearance.
Don't quite understand.. engine wasn't running right so you dynoed it?? or the engine went south while doing the pulls??
I apologize it's a complicated story but the engine wasn't running right. Seemed to be cutting out then that's when i was told it only had 91 in it. Put 110 race gas in and it sounded perfect and ran great. Didn't think to check deeper to see if anything was damaged. My stepdad and I knew we wanted it tuned and put on a dyno so we sent it up to a performance shop and after a few pulls with the race gas they checked plugs after some jetting and achieving the proper AFR. That's when they found the plug.. All other plugs look perfect.. Yes, they were changed recently, but they are the same number. The plug does seem to have a noticeable gouge in person after taking another closer look.. Looks like I'm pulling an engine! Posted using the Full Custom H.A.M.B. App!
If it were me I'd do another compression or leakdown test just to be sure that a) it's low, and b)find out where it's leaking from. There is a chance you have a piece of debris stuck to a valve seat. Same plugs as before eh? Could the old ones have been indexed to keep the electrode away from the piston?
^^^^^ that's a good idea. I will double check and find out where it's leaking. I don't believe the plugs were indexed.. Posted using the Full Custom H.A.M.B. App!
Blowby>>>Could the old ones have been indexed to keep the electrode away from the piston? >>> The only thing that suggests otherwise is that the plug looks like it had been firing OK for awhile, maybe not perfectly but firing. Though I guess it coulda been still firing in that mangled state if the electrodes aren't actually kissing --- can't tell too well from the photo. Anyway, if the plugs had to be indexed to avoid this, those are the wrong kinda plugs to use IMO. Jack E/NJ <!-- / message --><!-- sig -->
^^ it had been firing in the mangled state I believe. Engine didn't have a miss or stumble even at 6k rpm on the dyno. He pulled it and wasn't gassy or anything as well. The tuner put a new plug in and picked up 20hp.. Posted using the Full Custom H.A.M.B. App!
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