NewZed Posted January 6, 2013 Share Posted January 6, 2013 (edited) Thanks. Maybe .028" is the limit. I had posted in another thread about the fact that Honsowetz had said, in his "How to Modify..." book, to never go lower than .050" piston to head clearance and PMC and someone else replied back they both went about .028", but with forged components, not stock. Less stretch with forged, I assume. Anyway, it looks like you're on the edge. Good luck. Edit - Here's the post I was referring to. rsicard is the "someone else". He said .030", PMC said .028". With precise measurements and machine work mandatory for success, I would guess. http://forums.hybridz.org/topic/106806-long-rod-short-piston-combo-l28-tech-questions/?do=findComment&comment=999867 Edited January 6, 2013 by NewZed Quote Link to comment Share on other sites More sharing options...
skirkland1980 Posted January 6, 2013 Share Posted January 6, 2013 I'm running 0.032" on a sbc race engine. The only time I've heard of needing more than that was possibly with aluminum connecting rods. You also need to check how high each side of the piston top rocks out of the bore (with a dial indicator) and divide by 2. Quote Link to comment Share on other sites More sharing options...
JCan Posted January 6, 2013 Author Share Posted January 6, 2013 Guys. Thanks for your feedback. I think we are on the right track getting a custom gasket which would ensure my piston to head gap is 0.035". As soon as I get the new gasket and install it, I'll write up my results. thanks again Jim Quote Link to comment Share on other sites More sharing options...
Xnke Posted January 6, 2013 Share Posted January 6, 2013 Are you running stock flat-tops, stock rods, and stock crankshaft? If so, you should not be having a problem, UNLESS you had the block decked. If you did, then the thicker gasket might help, if you didn't and the crank-centerline-to-deck-surface isn't 207.85mm, then someone else did. 207.85mm is the "factory" distance, from crank centerline to top of deck (IIRC...could be oil-pan rail to deck, but I don't think it is) Quote Link to comment Share on other sites More sharing options...
Josh280z Posted January 7, 2013 Share Posted January 7, 2013 I just had a similar issue with my car, camshaft was degreed incorrectly. So maybe check that. Quote Link to comment Share on other sites More sharing options...
Z Greek Posted January 7, 2013 Share Posted January 7, 2013 In my humble opinion, you are chasing your tail with piston to head interference. Your method of measurement, straight edge, feeler gauges, etc., is not accurate, however, unless you decked the hell out of the block, you should be no-where near interference, especially at idle. I have taken apart a number of stock, running flat top engines, and have seen as much as .014 "out of the hole." Unless my feeble old age eyes are letting me down, I do not see what you are looking at in your picture in the earlier post, when you are referring to interference. The intake valve has a funny grainy appearance to it, but the quench pad looks fine. I would really keep looking. You say you shimmed your cam towers. Did you use thicker lash pads, and carefully reset your rocker geometry? Look carefully at your cam followers, is the cam running off the back of the pad? Quote Link to comment Share on other sites More sharing options...
JCan Posted January 7, 2013 Author Share Posted January 7, 2013 Okay. Lots of things to consider. I am not sure of the history of the motor or the car as I just purchased the car from a guy who had it on a farm in stockton for 11 years.... Background. I tried to be careful in measuring clearances during engine re-assembly (see below picture of excel spreadsheet). On my setup, the piston rises above the deck by 0.025" and with a 0.049" gasket this leaves 0.024" of gap between the top of the piston and the head. the first spreadsheet shows my measurements and calculations during initial assembly. The second spreadsheet shows what I will have after I install the custom head gasket (0.063"). You comment is accurate. I may be barking up the wrong tree! My brother thinks the problem is with the cam and lashpads. I know I can repeat the noise (not as loud) if I tap the rocker arm onto its lash pad (when not engaged with the cam). Regarding timing. I think I timed the engine correctly, but how can having the timing cause a loud tapping noise each time the engine turns a revolution? I will certainly recheck my timing. Regarding rocker arm cam. I took the head to the guys that built it and they said it looked ok. Their suggestion was to call isky and talk to them regarding the geometry. Again, I will report my findings this weekend when I install the new head gasket and completely eliminate the piston to head clearance as being a problem. Brian (my son) and I are looking forward to show the car at the motorsport west coast show. Thanks Jim Quote Link to comment Share on other sites More sharing options...
Z Greek Posted January 7, 2013 Share Posted January 7, 2013 (edited) Your head gasket, depending on what it is made of, will compress to a different thickness than it was in the package. Not sure whether the 1.6 number you are using is before, or after torqued. All that being said, you should have more than enough piston to head clearance. I think you probably did before, also, but without knowing exactly how far out of the hole (negative deck clearance) you had before ( I know you measured with a straight edge, and feeler gauges, but in my opinion, honestly, trying NOT to be a smart ass, that is really not accurate enough), you may never know. When you measure piston deck clearance, you need to be really careful, when the piston is "parked" at tdc, it rocks, and deck clearance changes pretty dramatically, .004-.006 depending on piston to bore clearance. A proper fixture, and a dial indicator are the only accurate way to measure deck clearance that I know of. All that being said, I would be looking real hard at your valve-train. You said in the intro to this post that you had your head milled .080, and have cam tower shims. I am going to make the assumption that you shimmed the cam towers the same amount you milled the head? Next you say a "mild cam". Any reground cam will almost certainly have a smaller than stock base circle. Let's just say for arguments sake, your "mild" cam has a base circle diameter .050 smaller than stock. So now you have your cam .105 further away from your cam followers than it was stock. In order to correct this, your cam followers have to move pretty much straight up. In other words, approximately the same distance taken up on the adjuster end, and at the lash pad. Assuming my assumptions are accurate, you should have lash pads approximately .225 thick. If they are dramatically different than that, you might look really close at your cam followers on either end of the pad, but mostly on the "pivot" side. Look at 'em really closely regardless! Good luck, sorry to hear your having trouble! Edited January 7, 2013 by Z Greek Quote Link to comment Share on other sites More sharing options...
PMC raceengines Posted January 7, 2013 Share Posted January 7, 2013 Have you run it with the rocker cover off ,, i have seen many covers hit the rocker gear and make this noise Quote Link to comment Share on other sites More sharing options...
JCan Posted January 7, 2013 Author Share Posted January 7, 2013 What a mess that was! I unscrewed the rocker arm cover with the engine running and lifted it up. No the noise did not stop and yes I needed a beach towel to mop up the oil mess under the car. Needless to say, that was not the problem. Thanks for your suggestion. Jim Quote Link to comment Share on other sites More sharing options...
TimZ Posted January 7, 2013 Share Posted January 7, 2013 What a mess that was! I unscrewed the rocker arm cover with the engine running and lifted it up. No the noise did not stop and yes I needed a beach towel to mop up the oil mess under the car. Needless to say, that was not the problem. Thanks for your suggestion. Jim Did the noise get louder or did it stay the same? Quote Link to comment Share on other sites More sharing options...
JCan Posted January 8, 2013 Author Share Posted January 8, 2013 With me holding the cover up by 1 inch and moving it around the Noise stayed the same. thanks Quote Link to comment Share on other sites More sharing options...
Josh280z Posted January 10, 2013 Share Posted January 10, 2013 (edited) Is it anything like this??? Edited January 10, 2013 by Josh280z Quote Link to comment Share on other sites More sharing options...
JCan Posted January 10, 2013 Author Share Posted January 10, 2013 Josh. No. I pulled the plugs and measured compression. My compression was 230psi at #6 down to 190ps1 at #1 The compression seemed to drop evenly as I moved from #6 to #1 (making me think the reason for the difference was that the car was not level and #6 got more oil than #1). During this measurement. There was no sign or sound of any tapping. The tapping did sound like a loud valve but only on one cylinder. FYI the new head gasket is in fedex now. Hope to have an update fri eve. Thanks for your good idea. Jim Quote Link to comment Share on other sites More sharing options...
JCan Posted January 13, 2013 Author Share Posted January 13, 2013 BAD NEWS! I added a thicker head gasket and the noise continued. Therefore I believe the noise is coming from the head and specifically from the valve train somewhere. I took a video and appreciate your ideas as to what to do next. (noting I have a backup N42 head, but I would prefer to use my completely rebuilt P90 head) Here is what I know. I believe the noise is related to only one piston and not all 6 The sound comes from the valve cover, I removed the cover using my hands when it was running (oil leaking everywhere) and the noise was not attenuated Cam - Isky My plans are as follows: Wait till sunday, then regap the intake/output valves to 0.006/0.008 intake/Output and re-run the engine. On monday, I plan to call Isky cams and ask them for ideas. If isky has no ideas, I plan to swap out the existing cam for the old cam inside the N42 head. If that does not solve the problem, then I plan to remove the head I spent so much money on and re-install the N42 head. Attached is a video of the noise. Thanks for your advice. Jim Quote Link to comment Share on other sites More sharing options...
JCan Posted January 13, 2013 Author Share Posted January 13, 2013 Video is at the below link. http://http://youtu.be/rc-TE_wGupM Quote Link to comment Share on other sites More sharing options...
NewZed Posted January 13, 2013 Share Posted January 13, 2013 (edited) Link doesn't work and youtube is misspelled. If you get the head off again maybe you could rig up a drill motor to spin the cam on the bench. Should be enough oil already there to keep things lubricated and you can watch each valve moving. Support the head by the ends and the valves can open and close freely. Or stand it on end. A piece of hose from the drill chuck to a bolt head makes a good flexible coupler. Have you done a pressure check to make sure each valve is closing properly? Maybe you've got a bent one that is hanging and getting dinged by the rocker arm. Edited January 13, 2013 by NewZed Quote Link to comment Share on other sites More sharing options...
JCan Posted January 13, 2013 Author Share Posted January 13, 2013 yes. I did a compression test. 230PSI on #6, to 190 PSI on #1. I believe the difference was caused by the motor being on a slant and had more oil on #6. Youtube link is Thanks Jim Quote Link to comment Share on other sites More sharing options...
NewZed Posted January 13, 2013 Share Posted January 13, 2013 You might run that pressure test again, or a leak down test A slanted motor shouldn't cause a 17% drop from high to low. Reporting the values from all cylinders would tell more also, not just two. That link works. Sounds terrible. Good luck. Quote Link to comment Share on other sites More sharing options...
Lazeum Posted January 13, 2013 Share Posted January 13, 2013 I don't have the feeling the car sounds that bad. Maybe, I've got the same issue then. Have you tried again to adjust your valve train? I'm sure the answer would be yes but I'm asking still How does the sound change while driving in higher rpm? I'm wondering if it couldn't also be related to the cam? A friend is running a 3.2L from Rebello, It makes tons of noise on valve train & apparently it is normal. I'm running a Rebello cam also on my engine for info. Maybe you should ask Isky who machined your cam some inputs on your situation. Quote Link to comment Share on other sites More sharing options...
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