theeoracle Posted February 14, 2016 Report Share Posted February 14, 2016 I need new lash pads for a reground cam and I cam across this formula on datsunparts.com I was wondering if it actually works and to make this whole process easier and so I don't have to cut up a feeler gauge. this is based on the 1.396 rocker arm ratio. FORMULA: Use the following example and plug in your own numbers. Base circle diameter of your camshaft ___ subtracted from the constant 1.310 = ____ divided by 2 = ___ + original lash pad thickness of .078 = ___. Select a lash pad thickness from our stock as close to this thickness as possible. and what does constant mean? 2 Quote Link to comment
G-Duax Posted February 14, 2016 Report Share Posted February 14, 2016 It's the number that you always use, and represents the stock set up (cam base circle). And it's one, two, three, what are we fighting for. Five, six, seven, ain't no need to wonder why, we all are going to die.......... Sorry, flash back there ! 2 Quote Link to comment
Doctor510 Posted February 14, 2016 Report Share Posted February 14, 2016 OK guys, This the way haven doing it for over 30 years. You will have to do this on two cam lobes, 1 intake and 1 exhaust. Install a STOCK lash pad, thickness is .120" turn the adjuster bolt up until you have 2.5 - 3 threads showing above the big lock nut. Measure the clearance you may have to stack feeler gauge blades, ADD that figure to .120" for your lash pad thickness. Example: stack of blades = .080" add that to .120" You need a .180" lashpad 1 Quote Link to comment
DanielC Posted February 14, 2016 Report Share Posted February 14, 2016 Doesn't .080 + .120 = .200? 3 Quote Link to comment
G-Duax Posted February 14, 2016 Report Share Posted February 14, 2016 I like the way theeoracle found better. Quote Link to comment
john510 Posted February 14, 2016 Report Share Posted February 14, 2016 I need new lash pads for a reground cam and I cam across this formula on datsunparts.com I was wondering if it actually works and to make this whole process easier and so I don't have to cut up a feeler gauge. this is based on the 1.396 rocker arm ratio. FORMULA: Use the following example and plug in your own numbers. Base circle diameter of your camshaft ___ subtracted from the constant 1.310 = ____ divided by 2 = ___ + original lash pad thickness of .078 = ___. Select a lash pad thickness from our stock as close to this thickness as possible. and what does constant mean? L-series motor or U-series motor ? they have different rocker ratios and lash pad thickness stock. Quote Link to comment
datzenmike Posted February 14, 2016 Report Share Posted February 14, 2016 L series rocker arm ratio is 1.48 The stock base circle diameter is 1.3 or a base circle radius of 0.650" on a stock cam. If your new or reground cam has a base circle diameter of 1.2 or radius of 0.600" subtract from the stock 0.650" to get 0.050" difference. Multiply by the rocker ratio 1.48 to get 0.074". This is how much more the lash pad must be increased in thickness to come out CLOSE to stock. Close not exact. You must do a wipe pattern to confirm and maybe tweak it some. 2 Quote Link to comment
Rick-rat Posted February 14, 2016 Report Share Posted February 14, 2016 Doesn't .080 + .120 = .200? :thumbup: 1 Quote Link to comment
Stoffregen Motorsports Posted February 14, 2016 Report Share Posted February 14, 2016 Any which way you look at it, you still need to verify the wipe pattern before it's a done deal. 2 Quote Link to comment
Rick-rat Posted February 14, 2016 Report Share Posted February 14, 2016 OK guys, This the way haven doing it for over 30 years. You will have to do this on two cam lobes, 1 intake and 1 exhaust. Install a STOCK lash pad, thickness is .120" turn the adjuster bolt up until you have 2.5 - 3 threads showing above the big lock nut. Measure the clearance you may have to stack feeler gauge blades, ADD that figure to .120" for your lash pad thickness. Example: stack of blades = .080" add that to .120" You need a .180" lashpad Doesn't .080 + .120 = .200? That must be the new math they teach these days 3 Quote Link to comment
Doctor510 Posted February 14, 2016 Report Share Posted February 14, 2016 That must be the new math they teach these days Come on guys, I'm almost 80 YO and I hadn't had my coffee yet. Good catch... Quote Link to comment
datzenmike Posted February 14, 2016 Report Share Posted February 14, 2016 Coffee. That's the excuse I use. 2 Quote Link to comment
banzai510(hainz) Posted February 14, 2016 Report Share Posted February 14, 2016 OK this is what I do. I buya whole set from .150 to .200 and then install the correct size. Everything is based on a uncut head so some of the OP math will come out wrong with head was shaved. valves cut seats cut and if a regrind cam installed(usually about in the 180 190 range if anything. New Cam in 150-160 range(My Schneider) stock uses a dished back side lash pad. all the perf lash pads are flat bottom surfave so bigger retainers will be needed so they don't flop out. Baz at Datsport told me believe he has sucken back side lash pads but haven't actually seen them. Quote Link to comment
Doctor510 Posted February 14, 2016 Report Share Posted February 14, 2016 OK this is what I do. I buya whole set from .150 to .200 and then install the correct size. Everything is based on a uncut head so some of the OP math will come out wrong with head was shaved. valves cut seats cut and if a regrind cam installed(usually about in the 180 190 range if anything. New Cam in 150-160 range(My Schneider) If the block surface has been cut, it not it will not affect the valve lash, if the top of the head has been cut, it may cause an issue. stock uses a dished back side lash pad. all the perf lash pads are flat bottom surfave so bigger retainers will be needed so they don't flop out. Baz at Datsport told me believe he has sucken back side lash pads but haven't actually seen them. Quote Link to comment
banzai510(hainz) Posted February 14, 2016 Report Share Posted February 14, 2016 wasn't sure on one of them. Key is to make sure the machinist gets the valves and seat close to also use one size lash pad Quote Link to comment
theeoracle Posted February 16, 2016 Author Report Share Posted February 16, 2016 L series rocker arm ratio is 1.48 The stock base circle diameter is 1.3 or a base circle radius of 0.650" on a stock cam. If your new or reground cam has a base circle diameter of 1.2 or radius of 0.600" subtract from the stock 0.650" to get 0.050" difference. Multiply by the rocker ratio 1.48 to get 0.074". This is how much more the lash pad must be increased in thickness to come out CLOSE to stock. Close not exact. You must do a wipe pattern to confirm and maybe tweak it some. I did some more thinking and this is the easiest way in my opinion of getting it as close to accurate as possible. and I did this calculation on my used regrind it came out to .179", so that means go with .180" pads right, that is is the stock datsun lash pads are .120" including the recess? and cam i use .180" pads with stock retainers? 1 Quote Link to comment
datzenmike Posted February 16, 2016 Report Share Posted February 16, 2016 If you say so. Without numbers I have to bow to your arithmetic answer. If you got 0.180" then I guess it's 0.180" Quote Link to comment
banzai510(hainz) Posted February 16, 2016 Report Share Posted February 16, 2016 180s are falt on bottom and lot hangs out the top and should get support otherwise they will flop out. thats why the taller retainer. I havent done it. I always get taller retainers Quote Link to comment
theeoracle Posted February 17, 2016 Author Report Share Posted February 17, 2016 If you say so. Without numbers I have to bow to your arithmetic answer. If you got 0.180" then I guess it's 0.180" the radius of my stock base circle is .6575 and the radius of the new cam is .6175". .6575 - .6175 = .04 X 1.48 = .0592 + .120(stock lash pad height) = .1792" + . 001" or for lash or whatever. With your infinite wisdom, would it be best to get new retainers too with a .180 pad? Quote Link to comment
datzenmike Posted February 17, 2016 Report Share Posted February 17, 2016 Hainz recommends it. I admit that they do look kind of top heavy with the taller lash pad but the same amount of material hold them in as the stock 0.130. 50 thou is just over 1mm or two thumb nail thicknesses. Quote Link to comment
theeoracle Posted February 17, 2016 Author Report Share Posted February 17, 2016 180s are falt on bottom and lot hangs out the top and should get support otherwise they will flop out. thats why the taller retainer. I havent done it. I always get taller retainers where do you get your lash pads and retainers? Quote Link to comment
scooter Posted February 17, 2016 Report Share Posted February 17, 2016 You guys still have short pads, i have .230 pads with a .080 valve tip pad on the valve itself for a total pad height of .310. Thats with deep retainers Quote Link to comment
Doctor510 Posted February 17, 2016 Report Share Posted February 17, 2016 where do you get your lash pads and retainers? Schneider Quote Link to comment
theeoracle Posted February 17, 2016 Author Report Share Posted February 17, 2016 Schneider Schneider says they are out of stock on lash pads and on retainers they don't tell me min/max lash pad height Quote Link to comment
banzai510(hainz) Posted February 17, 2016 Report Share Posted February 17, 2016 Nissanmotorsport book has the part numbers for retainers and lash pads. But this is when I got them when still in Cilf. Now they in Tennesee. Here is why I suggest Isky cause they seem to have it on hand. Scheider was fine back when they still had the suff for my cam kit On your own on this. try a Z car shop Be honest if your no going to put dual twin choke carbs dont even bother with the hassle( this is just me) Quote Link to comment
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.