RickB Posted March 12, 2001 Share Posted March 12, 2001 I have pasted a response from another thread and wanted some input from you all. First some background, Friday night I ran the car through the 1/4 mile for the first time in a while. Turns out my tires are too short and I revved the car hard through the traps. I don't know how high but I ran out of camshaft and the car nosed over (12.12@110+). I should have shifted into OD. I trailered a wounded GN home for a guy and drove my car as it was fine. Next night I went cruising and no problem. I went out on a back road and got on it...no prob until i turned the next corner and I started getting a knock under load. Car runs fine, no percievable knock at idle. I pulled the valvecovers and all the rockers are tight and oiling well. thanks in advance for your responses... >>> quote: -------------------------------------------------------------------------------- Originally posted by Ray: Rick it actually sounds like a collapsed piston... rods usually knock at idle more beause of the lower oil pressure. If you caught it early enough where it didn't score the cylinder you may be able to just hone it a little and throw a new piston in... Does your motor have cast pistons??? If so you found the weak one.... Have you isolated which cylinder it is??? This may be cheap to fix.... --------------------------------------------- Ray...thanks for your response. Question...yes, i have cast pistons (as far as i know?). If the piston "collapsed" then wouldn't I have some smoke as an indicator? I plan to get it up to a friends shop so i can put it on a lift and pull the pan. First I will pull a plug wire at a time and see if thast takes the load off a cylinder so i can isolate it. Actually, i think I'll make this a new thread. thanks again, ----------------------------------- ------------------ RickB@DragRacer.com 280V8 http://www.rickb.racemail.com [This message has been edited by RickB (edited March 12, 2001).] Quote Link to comment Share on other sites More sharing options...
Scottie-GNZ Posted March 12, 2001 Share Posted March 12, 2001 Rick, as far fetched as this might sound in your case, I had a similiar problem a long time ago and it turned out to be a bad distributor advance spring that was causing too much advance and severe knock under extreme load. Before you dive into the engine, take the engine to maximum stall while some brave soul looks at the timing advance. Do not remember what the numbers should look like for a SBC, but it might be worth a check. I would think a rod would also knock at idle. ------------------ Scottie 71 240GN-Z Scottie's GNZ Quote Link to comment Share on other sites More sharing options...
Jeff Posted March 12, 2001 Share Posted March 12, 2001 Rick, The only experience I've had with a rod knock is exactly as you describe. It was a big block motor and would only knock in the upper revs. Turned out there was very little damage to the bearing and crank and therefore would only knock under severe load. I hope the problem is ignition as Scottie described. Good luck with it. Quote Link to comment Share on other sites More sharing options...
John Scott Posted March 13, 2001 Share Posted March 13, 2001 I've had two situations that mimicked rod knocks. first was a camshaft that had too much play in the block causing one of the lobes to strike the block under load. Ouch! That trashed all the cam, bearings and a cylinder wall. The other was loose converter bolts. Sounds crazy but they really do sound like a bad engine knock when they loosen. I hope you find something like the latter. Good luck. JS Quote Link to comment Share on other sites More sharing options...
pparaska Posted March 13, 2001 Share Posted March 13, 2001 Rick, the issue that bothers me is that this happened after going around a corner while you were "getting on it". My fear is you uncovered the oil pump pickup for too long while cornering and lost oil pressure momentarily and damaged a bearing. Journal bearings need that oil film, and if it gets scraped and thrown off and not resupplied, bad stuff happens. That being said, I had a Holley mechanical fuel pump that made a rod knock type noise in a SBC. It drove me nuts until it gave up the ghost and I put a new one on. It was deeper sounding than a valve tap, but not as viscous as a rod knock, so I thought maybe it was a piston pin problem or a slight rod bearing problem. Never went away or go worse, so that wasn't it. The damned fancy chrome fuel pump was the problem. Or the fuel pump shaft was too short for it. What did I know, I was a 17 year old kid who'd just built my first motor. Good Luck, ------------------ Pete Paraska - 73 540Z - Marathon Z Project pparaska@home.com Pete's V8 Datsun 240Z Pages [This message has been edited by pparaska (edited March 12, 2001).] Quote Link to comment Share on other sites More sharing options...
Kevin Shasteen Posted March 13, 2001 Share Posted March 13, 2001 Oh man....Rick, Rick.....Rick(?) I'm really sorry to hear you're having trouble. I'm only gone for a few days & come back to hear you're having rod knocks. Everybody; I met Rick & witnessed him/his car in action Friday night; Nice guy & a very clean sleaper of a Z. Rick; if you dont mind....(I know you're having prob's but I'm still gonna brag for you). Everyone (I know the run he probably rev'd too hard on) Rick was up against a 'fully unstreetable' & Trailored mid 60's Stepside Chevy that had been tubed; It's front end lifted on every run it made prior to going up against Rick. It sounded pretty bad & had ran some good runs prior to staging next to Rick. I dont think Rick had used the Nitrous up to that moment & still ran low 13's (13.1 & 13.2's). My buddy & I were hoping Rick could catch/pass him w/nitrous. Well Rick did catch him but didnt pass him. The Chevy let up at the end & still managed mid 11's (it was a fast truck). Still an exciting race. It literally looked like Rick was about to pass him. Rick, Really So...SO Sorry to hear you're having prob's & hope it turns out its just an "IGNITION" problem & dont actually have a rod knock(?)! Kevin, (Yes,Still an Inliner) Quote Link to comment Share on other sites More sharing options...
RickB Posted March 13, 2001 Author Share Posted March 13, 2001 Thanks for all the replys folks...it would be fun to have events that we could all put names, faces and cars(!) together huh. I have the car on my trailer here at work and will work on diagnosing it tonight when I have access to a lift and a couple of "2nd opinions". Ya' never know...it could be loose torque convertor bolts (been there), or even carbon (seen it happen). Worst thing I'll get an "opportunity" to improve it huh!! I'll keep you all posted. Kevin, thanks for the kind words. BTW, non nitrous pass was a 13.04@104+ and juice was a run out of gear 12.12@110+. Pete, I wasn't getting on it around the corner. I just first noticed the knock after making the next turn. Your point is well taken though and valid were that the case. Thanks again for or all the suggestions. ------------------ RickB@DragRacer.com 280V8 http://www.rickb.racemail.com Quote Link to comment Share on other sites More sharing options...
Ray Posted March 13, 2001 Share Posted March 13, 2001 Just for piece of mind you might want to pull the pan and check the bearings if you are putting it on a lift.. While you have the pan off look arround and cut the oil filter apart, this may give you more to go on is it is somthing weird... One thing I didn't ask was has your oil pressure changed any??? As for the piston if only the pin moved and the whole piston hasn't cracked the oil rings will still be in tack and doing there job... Everyone has brought up some good points, I agree do some basic trouble shooting before you tear into the motor. Let us know what you find??? BTW In the mid 80's I saw quite a few 302 Ford truck motors with this problem.. They would knock bad with a load on them but ran fine and had no other visable problems. When we pulled them down the only real problem we found was the piston pin boss was hammered and had alot of clearence. Ford even had a service buliten out about a bad batch of pistons in 302's... these motors all had medium to low miles most of them we just honed and put new pistons in...FYI ------------------ Remember it is only a piece of metal. Quote Link to comment Share on other sites More sharing options...
RickB Posted March 13, 2001 Author Share Posted March 13, 2001 Thanks again for more feedback. Oil pressure has remained consistant. I fired it up this morning to load it on the trailer and didn't notice any knock. Of course I wasn't bringing the rpm's up either. I'll be checking it out soon. ------------------ RickB@DragRacer.com 280V8 http://www.rickb.racemail.com Quote Link to comment Share on other sites More sharing options...
Andrew Bayley Posted March 14, 2001 Share Posted March 14, 2001 Rick, I feel your pain. How's this sound, you tell me why my transmission is leaking so bad and I'll diagnose your engine knock. ...how accurate does my diagnosis have to be? -Andy ------------------ "But I don't sit idly by, I'm planning a big surprise." Andrew's Land of Z and Honey Quote Link to comment Share on other sites More sharing options...
RickB Posted March 15, 2001 Author Share Posted March 15, 2001 It appears to me that it is most likely a rod or maybe a wrist pin on the right bank of the engine. I have it up at a friends shop now i just need some time. Shouldn't be too big a deal. RickB ------------------ RickB@DragRacer.com 280V8 http://www.rickb.racemail.com Quote Link to comment Share on other sites More sharing options...
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