Datsun Roadster Forum-311s.org

I just got my SRL camshaft reground by Delta Camshaft to take care of some minor pitting on a couple of lobes. I asked for an A grind and told them that I didn't want the base circle changed.

Well, it appears that they didn't read the note and/or used the wrong template because after I installed the cam and before I did any adjustments, there was a gap between the cam lobes and rockers of about .028". I've adjusted a couple of the rockers to get the right cold clearance (.006" Intake and .010 Exhaust) and I had to extend the rocker adjustment bolts by about 5mm. The middle rocker in the attached picture has been adjusted to the right cold clearance and the other two rockers are at the adjustment of the pre-ground cam.

With the rocker adjusted up this much the cam lobe gets really close to the edge of the rocker pad on the approach side. It's still contacting the machined surface, but the wipe surface isn't centered. I don't have any experience with this but it doesn't seem right to me. My questions to someone with experience are:

Should the rocker to cam lobe clearance pre and post regrind be about the same if it's kept stock (within a few thousands) or is this amount of difference normal?

If they screwed this up will they be able to build the lobes back up and regrind or is that too much of a rework?

If I'm stuck, do I have any other option than thicker lash pads? If not, where's a good place to get them?

Thanks for your time and all input is appreciated.

Roy Cannon

There are some here: https://datsunparts.com/collections/cyl ... d-set-of-8

check out this section for other parts: https://datsunparts.com/collections/cylinder-head-u20

Hmmmm, 1) Delta knows what they are doing. While they are not immune from mistakes, that would be a big mistake and unnecessary to cut a lot off the cam when all you're doing is cleaning it up (they have done cams for me for years, including clean ups); 2) when you removed the cam I would assume you had to back all the rocker adjustments off in order to get the rockers out (and back in) in the first place (?). I've never removed a cam without removing and resurfacing the rockers as well, but the resurfacing may not have been required if it was just a clean up and they were undamaged/worn as well. You don't want to install a cam with the rockers in place as 1) you'll be forcing it down with the cam cap nuts, and 2) you really should be installing the cam so it can spin freely while you tighten the nuts to make sure it doesn't bind and can spin by hand, THEN install the rockers (this can be difficult sometimes. Max looseness on the adjusters, use a screw driver to push down the spring, or a spring compressor (I have a certain one that works, can post a pic if needed, made for OHC engines).

As noted, you want the cam to wipe on the rocker more or less in the middle of the pad, or back where it was. As long as it's wiping on the pad and not off the edge you'll be OK, but to be sure I would want to know where it's wiping. So, what you need to do is to remove an intake and exhaust rocker (any), clean it of oil, then take a sharpie or use what's called "bluing" and cover the rocker pad surface, then reinstall the rocker, adjust it up some to close the gap (doesn't need to be spec, so don't stick a feeler gauge in there, it will wipe off the sharpie), then spin the cam around to wipe the rocker, then back the adjuster off again and remove the rocker to observe where it's wiping (choose a cylinder where you know the piston is not at top dead center or at the top of the stroke so the valve doesn't hit the piston). You can probably see how close it is to the old pattern, but more importantly that it's not off one end or the other. It is nearly impossible to tell by just looking at how it "appears" to wipe when assembled without doing this... it looks like it gets very close to the edge when it doesn't. If, after doing this, it clearly wipes wrong then I would contact Delta to ask more questions, and have your rockers sent off to be resurfaced so as to start clean. Then, it will be important to do this for each one (preferably all, but you can probably use a sample of an intake and exhaust as a guide for the others ASSUMING that all of the rockers adjust out to pretty close to the same height on the adjuster. Valve seats get worn and require more adjustment over time. The seats can get "pounded" into the head, and that will show up as little to no adjustment left, or one or more radically different exhaust or intake valve adjustments. In that case you're looking at head work). Anyway, based on the wipe you see, you add a thicker lash pad to move the location of the wipe on the pad until it's where you want it. As I said, a little difference one side or the other is not some huge issue, but wiping OFF the pad is. I'm gonna guess that you're actually OK, it just doesn't look that way.

Happy to post more, I've done this a lot. Hope this helps.

Thanks for all the great information Greg.
I did get the rockers resurfaced at the same time as the cam clean up. I didn't change the rocker adjustment nuts when I took the cam out or put it back in. When installing the cam, I put the rockers in first and rotated the engine by hand while I slowly tightened down the cam cap nuts. They seemed to go down smoothly. You're right about it being hard to tell exactly where the cam is contacting the rocker, especially with assembly oil on everything. I'll pull a couple of the rockers out, clean everything up and get the sharpie out. I'll post my findings.
Thanks again

How can you remove enough material from the cam and followers to clean them up and not have to readjust the valve clearance? If they do not remove any material from the base circle then removing material from the lobe will reduce lift and duration.

Glad to help! Agree with Keith, they had to take SOME material off, so they'll be a bit different. The wipe will tell you if there's a problem.

I was thinking they might take a couple of thousands off the base circle. The process as described on Delta's web page is that they fill any pits and then machine the excess filler off on a lathe. When I saw the clearance go from .006 to .028 and the adjustment nut change by about 1/4 inch it surprised me, especially when it appeared that the lobe was so close to the edge of the rocker.
Greg's suggestion to check the wipe with a sharpie was just what I needed to hear to relieve my concern. It looks like the wipe pattern has shifted by a couple of mm but I think it's still far enough from the edge of the rocker to call it good.
Thanks again for all the comments.

Oh good, yes those look great! It's good that you had the rockers done too so you put a new wear pattern on both. I'm glad we were able to help. I've had the same concerns myself so I knew what you were likely seeing. I would assume that the cam needs to be"broken in" like a new cam, so that's done by running the engine variably between 2500 and 3000 rpm or so for 15 minutes and not letting it idle for long until (ya, ya gotta sit there). That should lay down a new wear pattern and mate the two metals. Sounds like a hassle but it's a necessary step. Enjoy!

That doesn't sound like a hassle at all. I've got nothing better to do, I'm retired.
Thanks again for the info Greg.