Datsun Roadster Forum-311s.org

How exacting do lash pads have to be?

For example: Can a 2.10 be used with others that are 2.15 or 2.16, etc.

How about 2.2 and 2.1 or 2.2 and 2.3?

Or 1.9x and 2.1x, 2.2x (where the x can be anywhere from 0 to 9)

Hope this makes sense.

thanks

It's a good question Tim. Ideally, all the stem heights are the same, all the rocker arm pads and lash pads are all the same. That is the way it came from Nissan and each cylinder made a nearly exactly equal contribution to torque/hp.

Lash pad thickness directly affects cam wipe and cam wipe directly affects individual valve timing. So.... if you are trying to optimize the engine, you would want all the cylinders pulling the same and the most possible.

In the real world and 50 years post production, the only people who would optimize 4 individual cylinders to max and match is someone building a nationally competitive track car. Many, many hours for just that optimization effort.

So for a "taking the kids for ice cream" engine, you could mix and match lash pads without much ill effect. (you would still try to make the cam rocker wipe as visually similar as possible). Most importantly NO cam lobe wipes improperly off the rocker pad. That kills the cam.

On a full-on-high performance engine, optimizing valve timing for all 4 cylinders could easily make 10hp difference at max rpm, so if the difference between 210 and 220HP matters to you, that is one place to find that last 10hp (on an engine dyno).

For street cars, if the cam wipe is very similar, but not necessarily identical on all the lobes, you are fine.

JT68 wrote: ↑Thu Mar 30, 2023 12:51 pm It's a good question Tim. Ideally, all the stem heights are the same, all the rocker arm pads and lash pads are all the same. That is the way it came from Nissan and each cylinder made a nearly exactly equal contribution to torque/hp.

Lash pad thickness directly affects cam wipe and cam wipe directly affects individual valve timing. So.... if you are trying to optimize the engine, you would want all the cylinders pulling the same and the most possible.

In the real world and 50 years post production, the only people would optimize 4 individual cylinders to max and match is someone building a nationally competitive track car. Many, many hours for just that optimization effort.

So for a "taking the kids for ice cream" engine, you could mix and match lash pads without much ill effect. (you would still try to make the cam rocker wipe as visually similar as possible). Most importantly NO cam lobe wipes improperly off the rocker pad. That kills the cam.

On a full-on-high performance engine, optimizing valve timing for all 4 cylinders could easily make 10hp difference at max rpm, so if the difference between 210 and 220HP matters to you, that is one place to find that last 10hp (on an engine dyno).

For street cars, if the cam wipe is very similar, but not necessarily identical on all the lobes, you are fine.

Thanks JT, good information. I just took apart my U20 head and was thinking about the lash pads while cleaning them up in the parts washer. I still need to measure them, I haven't done that yet.

Florida Roadster wrote: ↑Thu Mar 30, 2023 1:04 pm
Thanks JT, good information. I just took apart my U20 head and was thinking about the lash pads while cleaning them up in the parts washer. I still need to measure them, I haven't done that yet.

Chances are they are stock unless someone rebuilt the head in the last dozen years or so. 2mm/.08" is stock. Old originals often have fairly deep wear grooves where the rockers ride (since they have been run for so many years). If there are no deep wear grooves, they probably got replaced over the years.

As long as the cam appears to be in the middle of the followers I wouldn't worry about the thickness. Where it gets dicey is if you have a big lift / duration cam which was most likely reground.