Babalouie Posted November 16, 2008 Share Posted November 16, 2008 Got a weird one when I swapped in a new cam. The old cam is in the background of this pic. You can see that there is quite a lot of material taken off the base circle of the old cam, and quite a big difference to the new one. The cam vendor crunched some numbers and recommended a 4.5mm/.180' lash pad. Mine turned out to be 5.0mm/.200', so we thought we'd install the cam with the old lash pads, check the wiping pattern and see. Maybe it's close enough. The problem is this...with the new cam in place, and the rocker pedestals screwed all the way down, I have zero lash. Just for experimentation' sake, if I remove the lash pad altogether, I get more room.... Well I get a lot more room at the pedestal end, but at the valve end I still don't seem to have much clearance. So the cause seems to be more than just a 1/2mm worth of variance in the lash pad...so I thought about installed spring height, maybe it's too tall. From head surface to retainer it's 50mm. I figure the next port of call is a much thinner lash pad, closer to stock size, just to see if maybe that fixes it. But I would have thought that the lash pads I already got would be in the ballpark....maybe the wrong wiping pattern, but not so far out that it would be zero lash with the lash adjusters all the way down... Anyone got any ideas? I should point out that this is an "unknown" engine, it came with the car as-is, and even with the old cam it didn't run all that well. Quote Link to comment Share on other sites More sharing options...
1 fast z Posted November 16, 2008 Share Posted November 16, 2008 Sunk Valves? Quote Link to comment Share on other sites More sharing options...
Babalouie Posted November 16, 2008 Author Share Posted November 16, 2008 Thanks, that makes perfect sense...and I guess the solution would be cam tower shims? Quote Link to comment Share on other sites More sharing options...
josh817 Posted November 17, 2008 Share Posted November 17, 2008 Cam tower shims indeed, and then probably an adjustable cam sprocket too. I had this problem too on my head, only with getting the rockers on. I used a screw driver to lift the rocker up onto the lifter head. It was rough doing all 12 because you are compressing the springs while you do it and trying to avoid the cam BUT once it was on the lifter head there was plenty of room. It appears you have no room at all even with the rocker on the lifter. I would check your lash pads, smaller ones will lower it but not enough for what you need I'm betting. To avoid wrestling the rockers in and since you're taking the cam towers out anyways for shims, place all the rockers one and then bolt the cam tower down and torque to spec. Its going to suck having to take off the chain and loosen all the head bolts. Since the cam towers use half the head bolts to hold them down I do believe, actually I think its 4 bolts on the one side... Back to the point though I would retorque the entire head when you assemble it again. Start al over and do all bolts over again to prevent any problems. Quote Link to comment Share on other sites More sharing options...
Babalouie Posted November 17, 2008 Author Share Posted November 17, 2008 Cam tower shims indeed, and then probably an adjustable cam sprocket too. I had this problem too on my head, only with getting the rockers on. I used a screw driver to lift the rocker up onto the lifter head. It was rough doing all 12 because you are compressing the springs while you do it and trying to avoid the cam BUT once it was on the lifter head there was plenty of room. It appears you have no room at all even with the rocker on the lifter. I would check your lash pads, smaller ones will lower it but not enough for what you need I'm betting. Yes, that thought occurred to me too. Smaller lash pads will make maybe 50thou difference but it seems like I need 200thou To avoid wrestling the rockers in and since you're taking the cam towers out anyways for shims, place all the rockers one and then bolt the cam tower down and torque to spec. Its going to suck having to take off the chain and loosen all the head bolts. Since the cam towers use half the head bolts to hold them down I do believe, actually I think its 4 bolts on the one side... Back to the point though I would retorque the entire head when you assemble it again. Start al over and do all bolts over again to prevent any problems. It's an option...I know the cam spins freely in the towers when I put the cam/towers back in. Quote Link to comment Share on other sites More sharing options...
ozconnection Posted November 17, 2008 Share Posted November 17, 2008 This may seem obvious, but have you actually installed a rocker arm to see how it is in its proper working position? Without doing this, looks can be deceptive. Also, get the thinnest lash pad you can (0.150), instal it and go from there. Quote Link to comment Share on other sites More sharing options...
Babalouie Posted November 17, 2008 Author Share Posted November 17, 2008 This may seem obvious, but have you actually installed a rocker arm to see how it is in its proper working position? Without doing this, looks can be deceptive. Also, get the thinnest lash pad you can (0.150), instal it and go from there. Yeah, I did. I got both rockers in place for #1 cyl, and there was no valve lash at all, and in fact the valve was cracked open a hair. That would explain why it was so difficult to lever the valve spring down enough to get the rocker in Quote Link to comment Share on other sites More sharing options...
ozconnection Posted November 17, 2008 Share Posted November 17, 2008 What thickness lash pad did you use? Quote Link to comment Share on other sites More sharing options...
Babalouie Posted November 17, 2008 Author Share Posted November 17, 2008 What thickness lash pad did you use? 200thou/5mm. Cam vendor said that the ideal lash pad based on the base circle of the cam would be 180thou/4.5mm. So the lash pad ain't that far out of the ballpark. Quote Link to comment Share on other sites More sharing options...
ozconnection Posted November 17, 2008 Share Posted November 17, 2008 200thou/5mm. Cam vendor said that the ideal lash pad based on the base circle of the cam would be 180thou/4.5mm. So the lash pad ain't that far out of the ballpark. Were the old lash pads all the same thickness? Yeah, I've done a few cam swaps myself. The 'supplied' lash pads were never the right ones. They're only guessing on what you need. Reconditioned/reworked heads are a different KOF compared with stockers. I'd go to somewhere like SWR and ask Stuart for a range of lashpad thicknesses. Ask if you can use them to see which one(s) will match your rocker/cam setup. Then you know what you need, how many and what thicknesses. Easy. I borrowed then bought several sizes because the dumbhead that did my seats didn't equalize valve seat depth in the head, so I had to use about 4 different sizes all the way along the valves to get the correct wipe patterns on the rockers. What a pain in the rear that was!! Now I'm sure to mention this whenever I get head work done (and the seats need attention for whatever reason). Be sure to try some thinner lash pads my friend. Cheers. Quote Link to comment Share on other sites More sharing options...
Babalouie Posted November 17, 2008 Author Share Posted November 17, 2008 Ta mate. I think that is the go...it won't hurt to put in a thin lash pad (just got to buy one as you say) and see if it makes all the difference... Quote Link to comment Share on other sites More sharing options...
ozconnection Posted November 17, 2008 Share Posted November 17, 2008 Ta mate. I think that is the go...it won't hurt to put in a thin lash pad (just got to buy one as you say) and see if it makes all the difference... You're welcome....borrow, test, then buy! Quote Link to comment Share on other sites More sharing options...
2eighTZ4me Posted November 18, 2008 Share Posted November 18, 2008 Hold the phone there guys. You're not replacing springs and retainers? Spring height and seat pressure for different cams tends to vary based on individual cam specs. I went through this recently with a couple cams. Started taking measurements and experimenting. The retainers that came with my Schneider cam varied radically from the retainers that came with my Racer Brown cam, as did those from a stock cam setup. There was as much as 1/2" difference between the two extremes. Knowing this, your installed height is going to vary, as is your wipe pattern. I started with .240 pads with the Racer Brown retainers, and ended up down at .180 pads with the stock retainers - just to keep the wipe pattern even on the mating surfaces. If you have sunk valve seats, you could be brewing a recipe for eating up a couple lobes of the cam, or at the very least, setting yourself up for a radical assortment of lash pads to get the wipe pattern correct. My guess is you have the aftermarket springs/retainers that came with cam A, and now you're trying to use cam B, which wasn't designed for those retainers/springs. I dunno - I'd be pulling that head - a head gasket and a few hours labor is far cheaper than eating up a cam kit. At the very least, measure installed spring height on each valve on the head, and (if you have another stock head) compare it to what stock height is. I'll bet they're not even close. This is my observation from experience. Search on "cam wipe pattern" and you'll see my thread complete with a lot of pics depicting a very similar situation, and showing side by side the differences in spring height JUST by changing retainers. Quote Link to comment Share on other sites More sharing options...
Babalouie Posted November 19, 2008 Author Share Posted November 19, 2008 Thanks for the tip. I think you might be right, the new cam is to suit stock retainers/springs and the old cam wasn't. I've got a couple of stock-size .120 lash pads, and I'll put them in just for experimentation's sake, but I think you're right, the head might end up coming off and being sent off to a pro cylinder head builder. Quote Link to comment Share on other sites More sharing options...
1 fast z Posted November 20, 2008 Share Posted November 20, 2008 Spring height has NOTHING to do with wipe patterns. The lash pad sits RIGHT on top of the valve, not the retainer. Spring height, matters for spring pressures and rates, but nothing with wipe patterns. Quote Link to comment Share on other sites More sharing options...
Babalouie Posted November 20, 2008 Author Share Posted November 20, 2008 Spring height has NOTHING to do with wipe patterns. The lash pad sits RIGHT on top of the valve, not the retainer. Spring height, matters for spring pressures and rates, but nothing with wipe patterns. Poor choice of words on my part....I meant installed valve height. I figure if the tips of the stems are too tall, then either the valves are cut into the seats a hell of a long way, or there are non-std valves with taller stems in there. Quote Link to comment Share on other sites More sharing options...
1 fast z Posted November 20, 2008 Share Posted November 20, 2008 I was mainly talking about this comment: I started with .240 pads with the Racer Brown retainers, and ended up down at .180 pads with the stock retainers - just to keep the wipe pattern even on the mating surfaces. Retainers will do nothing for wipe pattern. So this statement does not make sense. Quote Link to comment Share on other sites More sharing options...
Tony D Posted November 20, 2008 Share Posted November 20, 2008 I borrowed then bought several sizes because the dumbhead that did my seats didn't equalize valve seat depth in the head, so I had to use about 4 different sizes all the way along the valves to get the correct wipe patterns on the rockers. What a pain in the rear that was!! Now I'm sure to mention this whenever I get head work done (and the seats need attention for whatever reason). Is that the case on this head as well? My first thought was 'what is the valve stem height'? There is a specification for it, and that is what lash pad thickness is predicated on in conjunction with the base circle. If the valves are suck too deep (as 1fastZ suggested) you will never get the lash needed. A thinner pad is not the way to fix this, it may initially give you running clearance, but wipe pattern likely will be askew, as well as closing up as the engine runs in and you're screwed! Check valve stem height. If it's not correct, get the head builder to do the job correctly, and if that means he ruined a set of your seats by grinding on them and sinking the valves too deeply, then he needs to put in a set of seats and grind them to proper depth/height. Usually the problem with a reground cam is excessive clearance, not too little. Too little is almost always valve stems sitting up to high. You might be able to shim the cam towers to get acceptable clearances back. The cam to crank distance needs to be maintained, there is some tolerance there if your head hasn't been milled any... But the valve stems all need to be the same height for a proper vavle job. Quote Link to comment Share on other sites More sharing options...
Babalouie Posted November 20, 2008 Author Share Posted November 20, 2008 Thanks Tony Well this is a mystery engine that came with a car that was imported from Japan. So while there are lots of questions that I'd like to ask the engine builder, I can't. Does anyone know what the stock spec is for valve stem height? Quote Link to comment Share on other sites More sharing options...
ozconnection Posted November 20, 2008 Share Posted November 20, 2008 Have you tried any thinner lash pads in your engine yet? And have you tried the rest of the valve train to see if the problem is with all the rockers? It goes back to an earlier question I asked, were all the old pads the same thickness for that old cam? It may have been a case that the valve seats were machined too deep by the machinist but a mock up with the old cam, rockers, valves and lash pads worked out ok with a suitable rocker arm wipe pattern and it was left at that, deemed acceptable. This, rather than valve seat recession is what I'm thinking. Trying to put in a new cam with less material ground off it manifests itself with the problems your having. Bite the bullet and take the head off OR put the old cam back in, build a new head on the bench and swap them in one go. Is it a stock head on there ie no porting etc as far as you know? That would make it a much easier (and less expensive) decision IMO. Good luck mate. Quote Link to comment Share on other sites More sharing options...
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