question about valve tappets (lifters)

mike944 · 10-26-2003, 09:29 AM

Hi.

Do valve tappets (lifters) have to go back on the same cam lobe as they came off of?

I am looking at buying a rebuilt 968 head, but it still has the original cam & tappets. The person selling the head did NOT number the lifters, so i have no way of matching them up with their original cam lobe. can i put them anywhere? will i damage things when i start running?

I remember back from my days of playing with old american V8's that it was critical to not mix up the lifters, if you were re-using them. if they got mixed up, the cam could be destroyed very quickly. Lifters wear in to their particular lobe of the cam, and they all wear in slightly differently. Does this same logic apply to high-tech overhead cam engines? I would think it does, which means i would need new lifters and a new cam for this rebuilt head, or i would at least need to get everything resurfaced.

Anyone know for sure?

Mike

AFJuvat · 10-26-2003, 09:46 AM

Same rule applies to Porsche

You have to keep the lifters in the same cam lobe\valve.

Unfortunately, you must replace the tappets now

AFJuvat

mike944 · 10-26-2003, 09:58 AM

Can i just replace tappets, or do i have to replace the cam too?

SoCal Driver · SoCal Driver's Garage

You could use machinists blueing and see if you can match them. Would take a while but save you the plus $50 each.

mike944 · 10-26-2003, 05:37 PM

I was thinking about how to match them back up, i never thought of using machinist's dye. My other option, which i tried on a few scrap lifters that i had was to lap them flat again, using 2 micron diamond lapping compound. I used 2 lifters face to face. I have 2 issues with this way, 1. getting all of the compound off the lifters, and keeping it out of the engine. and 2. are new lifters really supposed to be flat?

If i can't seem to come up with a way to match them up, i'm probably going to just get a used, non-rebuilt head, because i really don't want to spend $650 on new lifters, on top of the $1600 for the rebuilt head i am going to look at. I'd rather just spend $1500 on a used head. I'll easily spend an extra $100 on a rebuilt head, but not $750 extra.

Mike

Makis · 10-26-2003, 10:22 PM

Well, if you are prepared to get another head, just use the existing head with the lifters until it goes. You will probably find out that you will be fine anyway. Also I don't think the lifters are flat from new, but I may be wrong.

mike944 · 10-27-2003, 05:36 AM

Makis - you must not have seen this thread Pics of my new 968 As you can see, i can't use the existing head, it's f'cked up. I HAVE to get a new head, as it's much cheaper than rebuilding the old one. I wish i could run with the existing one.

Socal - how well do you think i could match up the lifters? i have my doubts that i could do it adequately. I would really like to put a rebuilt head on instead of a used one.

Mike

SoCal Driver · SoCal Driver's Garage

My idea was to dye a lifter and cam lobe, hold them together and spin the cam by hand on a bench (Cam in the housing). If you do this with one lifter on all of the cam lobes you should see most of the dye rubbed off when they match up. As you progress the odds of getting the right combination increase and the time to complete goes down.

Other wise just stick the whole thing back to gether and see if they reseat.

Nigel Haslock · 10-27-2003, 11:39 AM

With regards to the thought of lapping two lifters face to face.

If you use two, you can make them mate but you cannot guarantee that they are flat. If you lap a set of three (1 to 2, 2 to 3 and 3 to 1), you guarantee that they will be flat.

mike944 · 10-27-2003, 12:00 PM

But are new lifter faces supposed to be flat? or are they supposed to be crowned?

I've never heard about using 3 parts before, I just came up with that method of making them flat, because i know that's how people re-face surface plates. Put 2 of them face to face, with a little bit of abrasive compound, and rub them until they are flat.

Nigel Haslock · 10-27-2003, 03:31 PM

I was thinking of a discussion of surface plates when I said that you need three to guarantee flat.

The reasoning is that with two, one could be convex and the other concave and both mate perfectly.

With three, number one could be convex, number two concave making number three convex again. Grinding one against three would wear down the convexness. The only way to get all three to mate is to get them flat.

I still have no idea if this is the desired shape for lifters.

Nigel