Detonation and advance

[Scotty_S-15]

So I notice that each time I\'ve raced my truck this year, I\'m experiencing a little blow-by. That is, I\'m seeing oil trying to escape around the PCV grommet, and weeping out of the front intake seal, obviously more crankcase pressure than normal. Not much oil, just that it hasn\'t happened before, and only when racing. Engine sees about 6,400.

..... So before I race last Friday, I pull the timing back a few degrees from 36 to about 33-34 total. And yes, TDC is proven. http://www.s10v8.com/images/smilies/icon_wink.gif

..... So I race, and guess what, no more oil trying to escape http://www.s10v8.com/images/smilies/icon_smile.gif and, considering the weather, looks like I may have picked up about 1 MPH. Hmmmm.

......... So, the question for the engine experts: Is it possible I was detonating a little, and \"rattling\" the rings? I can\'t think of any other explanation. Possible?

........ Oh yeah, about 10:1 compression, pump gas, Edelbrock Performer RPM heads (shaved .030) on a ZZ4 short block.

[coppergmc]

Detonation does some nasty things inside the cylinder. I\'d say it was possible you were having detonation problems that could have been shocking the rings. There really is too many variables involved to give a sure fire answer though. You should make some more timed test runs and see if pulling a degree or two out helps any. I would try 1 or 2 degrees at a time until you slow down. Keep an eye on trap speed. That\'s were you get the real answer on power production.

[Scotty_S-15]

I had been running the same setup & timing I used last autumn, and no blowby then.

...... Do you think the new 10% ethanol gasoline leaned me out enough where I needed to pull the timing back a hair? I know I\'m always on the lean side, without a \"rich\" cushion. My engine definitely makes more power lean.... but scary without that \"cushion\". hmmmm.

[dutigaf]

so your total timing is about 33 to 34..



have any idea what your base is just for shits and giggles.. im still tinkering with mine and have that same oil seeping problem. thought maybe i was a little too lean.

[grimpuppy]

On 2006-07-03 16:10, Scotty_S-15 wrote:

I had been running the same setup & timing I used last autumn, and no blowby then.

...... Do you think the new 10% ethanol gasoline leaned me out enough where I needed to pull the timing back a hair? I know I\'m always on the lean side, without a \"rich\" cushion. My engine definitely makes more power lean.... but scary without that \"cushion\". hmmmm.





I would look more in this direction than the detonation. 10:1 compression with aluminum heads shouldn\'t have any trouble with detonation at 36 degrees. Unless you are trying to use the cheap stuff http://www.s10v8.com/images/smilies/icon_razz.gif . I can see where your comming from though. I would try an jump up a couple jets and see what it does at your current timing. Then bump back up to your 36 degrees and see what it does.

Maybe it just likes 33 degrees of timing



Pulling 3 degrees of timing out and the oil leaks stopping is pretty strange.

http://www.s10v8.com/images/smilies/icon_wink.gif

[stroker1]

Interesting. You said you where using the same set-up and timing as last fall (autumn). How did the outside temp and humidity compare? Maybe taking some timing out compensated for the difference in fuel mixture. Just my thoughts, what variables would have caused you the detonation problems. If in fact thats what it was, and it does sound likely you where making more cylinder pressure SOMEHOW!!



Later, Stroker1

[Scotty_S-15]

Thanks for all the thoughts, guys. Regarding the increased crankcase pressure (hence blow-by): That\'s part of the reason I pulled the timing back in the first place. I theorized (maybe I read it somewhere) that under detonation the piston rings can rattle, or vibrate from the shock. I further theorized that this could lead to a loss of combustion pressure into the crankcase.

......... If this was the case, I hope I didn\'t damage anything.

.......... Regarding rich or lean, I\'m in the process as we speak, of hooking up my Innovate wide band 02 gizmo.



Sidenote: ragarding engine damage, I lost the original \"mild\" 13.2/102 mph 350 in the S-15 to too much advance. It was running crappy, put the timing light on it....... http://www.s10v8.com/images/smilies/icon_eek.gif http://www.s10v8.com/images/smilies/icon_eek.gif OK.... only 50+ degrees total... http://www.s10v8.com/images/smilies/icon_eek.gif http://www.s10v8.com/images/smilies/icon_eek.gif I\'ll never really know what happened, but except in the midst of all this I literally lost the outer ring of the balancer. I may have adjust the timing after it had slipped, hence wrong TDC, but not likely, because if I needed to advance it 15 degrees ant ANY time for no apparent reason, that surely would have caught my attention. BTW, still ran 13.5 with a chunk missing from the ringland, and a piece of ring stuck in the top of the piston.... http://www.s10v8.com/images/smilies/icon_razz.gif By then I was getting SERIOUS blow-by. http://www.s10v8.com/images/smilies/icon_wink.gif

[NoMoore]

Detonation is a secret killer. Sounds like you had some for sure. It will attack the ring lands from underneath, and rob power like a mo fo. Here are some plug reading sites to help you along. Good luck!!!







http://www.dragstuff.com/techarticles/plug-pictures.html



http://www.dragstuff.com/techarticles/how-to-read-plugs.html



http://www.strappe.com/plugs.html



http://www.dragstuff.com/techarticles/reading-alcohol-spark-plugs.html



http://www.dragstuff.com/phpBB2/viewtopic.php?t=22

[dutigaf]

ok guys im hanging in this thread just pickin your brains...



seems i ws a little lean, as it was noticable hotter on the passenger side.. so i put my little gauge on and tweeked the carb a little and the idle smoothed out and so on and its running a lot smoother and better all the way around. still getting a little oil seepage from both front and rear seals.. but man does it feel and sound way better. think i may be just a hair to advanced n my timing. its a fairly stock motor. oh and btw can you acutally buy a good balancer at a decent price now days that the ring is exactly where it belongs? ive checked three and they have all been off a good bit. thanks for any suggestions. duti

[Scotty_S-15]

Dut, don\'t worry about the mark on the balancer, just remark it, or the tab. That is, re-establish TDC using a sparkplug piston stop tool.

.....As for the advance, on a fairly stock engine, 12 degrees initial (base) and a total of 32-34 is a safe start. These checked with vacuum adv. disconnected, of course.

[dutigaf]

thansk for the pointers..



i took the timing chain cover off and got the dots lined up and put the mark on the balancer that way.. im not a pro engine builder. just a tinkerer. so i could still be off a little bit, looks like im sitting right at about 10 before on base timing so im gonna run it a few days and see. it is running way smoother, but still getting the seepage as you mentioned. its coming along little at a time. i\'ll keep checking in with result as i get them.

[Scotty_S-15]

Just to make it clear, detonation or overly advanced spark is one of the most UNLIKELY reasons for oil leaks, or oil being pushed out of breathers, etc.

....... As far as confiming TDC-timing mark accuracy, you\'d still need to get one of those \"piston-stop tools\" you screw into #1 spark plug, presuming the heads are on. I think they only cost about $10 or $15, and I\'d assume they come with instructions.

........ Lining up the dots on the timing gears is a must, but only affects cam timing. And even then, too many variables to say that the cam will be correct. 99% of the time, yes.

[dutigaf]

ok will go get one. lol



man it is running way better now thean before...



heres my idiot statement of the day...



could i be getting the crankcase pressurized from my rings not seated up yet? never had tht hapen before... and im pulling good vac* on my pvc.

[Scotty_S-15]

On 2006-07-09 21:57, dutigaf wrote:

....................... could i be getting the crankcase pressurized from my rings not seated up yet? never had tht hapen before... and im pulling good vac* on my pvc.



Sure, rings that aren\'t seated could create some blow-by, and create positive pressure in the crankcase.

* With the engine idling, leave the PCV in place, and pull the vent (fresh air intake) from the other valve cover, and cover with your hand. Pressure or vacuum? You should feel vacuum, providing the PCV is working properly.

* Or, if you pull out the PCV, is there a lot of pressure coming out of the crankcase? How about the crankcase vent on the other valve cover? Cover one or both with your hand(s), and see how much pressure builds.

[dutigaf]

yeah when i put my hand on the vent on the other side of the motor from the pvc ive got suction.... and even when i give it some gas from the carb still got suction no obvious blow by or pressure, but sure as shit when i pull in the garage after being out driving i get a few drops everytime that have ran down from the front seal and rear seal locations. and im only running about 45lbs of oil pressure when im up running and about 20-25 when im sitting still. i was real careful with the timing chain cover when i put it on, didnt install the seal dry or nothing like that.

[Scotty_S-15]

Oil leaks are the most common PITA. There are not many of us that\'s totally leak-free, I\'d guess. http://www.s10v8.com/images/smilies/icon_mad.gif I\'ve got a slight drip from the front cover, I suspect it\'s the cheapie 2-piece timing cover. My TH350? FuGetAboutIt. Got it down to very little leakage. I\'ll quit while I\'m ahead... barely. http://www.s10v8.com/images/smilies/icon_razz.gif