The Stovebolt Site Forums The Shop Area Engine Shop Talkin’ Tappets and their Cam Lobes!

Convex? Or flat? It’s rumored that the tappets had rounded bottoms so they would rotate.
But…I’ve got a box of NOS ‘54-‘55 261 tappets here in the shop and they’re as flat as flat
can be. Checked the original ones that came out of my ’59 261 on the surface plate and
guess what…..the faces are as flat as a Pugs puss.
http://www.pbase.com/dennygraham/image/161876786
Another way that an engine designer can rotate a lifter is by offsetting the lifter bore
centerline to the cam lobe. And if you look at the alignment of the lifter bores to the cam
lobes in this 261, some are offset….and some are not. Tapered cam lobe is another feature
used by some designers and in this engine, some of the lobes are tapered about
.004”……and…..some are not.
I don’t have any idea where you would find the specs on the cam and lifter design for these
engines to see what method was used, but it would be interesting to know. The taper
required in some cases is so slight it’s difficult to tell if it’s taper you’re measuring or just
normal wear. And, Vintage engines had flat cams, flat tappets, tapered cams, convex
tappets, and offset bores. Nothing cut in stone and every designer had his own idea of how
to get the most life out of the cam and lifters.

DG

Denny, I have used the back side of my old 645 Sioux for resurfacing lifters. It is a 50 to 60 year old machine, but it works. I set the angle between 1° and 2°. If you figure the radius of the lifter surface, the 1° to 2° angle will give you a crown, but I don't think it will be enough to measure the way you are trying to measure but it will cause the lifter to spin. If you Google something like "solid lifter resurfacing", you will find quite a few people companies that resurface them. Why not call them and discuss it with them.

I mess with Y-Blocks and GMC. They both require a crown on the lifter.

When I get time, I'm Probably gonna stop by the local engine
rebuilder and see if he's equipped to reface them. Haven't had
a chance to do any surfing for "solid lifter resurfacing", but
since things have been so slow around the bolt lately and I'm
waiting on parts so I'll take a look. Good idea, i.e. calling
around also thanks for the suggestion Ken.
Been on the lookout for some NOS "exact" replacements but that
seems to be a bust. Had the alarm set to bid on some NOS GM
rocker shafts in the box yesterday but I was in the barn when
the alarm went off and my "big old wife" just shut it off,
went back to her cooking show and told me an hour later when
I came in, "Oh, I shut your alarm off, what was that for?"
That pair of shafts had one bid and went for $9.99. Needless
to say I was not a very happy camper to be around the rest of
the evening.
Another wild idea on the lifters is to set up my high speed
die grinder in the lathe. Biggest obstacle there is the lack
of coolant and surface finish.
http://www.pbase.com/dennygraham/image/161885728/large
These lifters are definitely
not crowned. When you can check new ones on a granite
surface plate with no rocking there is no doubt they are
"flat".
The odd taper I'm finding on the lobes may account for the
fact that a few of the lifters still look very good and
others are dished, the worst one .010". I need to match
the lobe taper I see on some of the lobes to the lifter
face to see if they are connected. Still haven't found
any info on the cam lobe design for the Stovebolt other
than some lift and timing data.
http://www.pbase.com/dennygraham/image/161885727/large


DG

Denny, use a die grinder on the compound rest, and set it for a 1 Degree angle. Center the lifter up in a 4-jaw chuck and use a fine-grit Cratex rubberized wheel in the grinder. You'll get a mirror finish without needing any coolant. That's how I finish gun parts that need a super-fine polish. I use a 22K RPM electric die grinder for that type of work. Be sure to cover the lathe ways with a tarp or some other way of keeping the grit off the ways, and clean up thoroughly afterwards.
Jerry

That's the plan Jerry, did ya take a look at the picture of
the temp setup I dug up? Still unpacking stuff from those
boxes that made the BIG move in 2012.
24,000 rpm on that Craftsman Industrial die grinder. That one
is from back in the day when Craftsman made some halfway
decent tools. It's been in the family for better than half a
century, pop used it on his South Bend bench lathe when he was
alive.

Now, that's an idea, I mean the rubberized abrasive. I've
got/had a couple of the 1"x 6" 3m wheels on pedestal grinders
in my shop for many years. I use them for deburring and
blending edges on parts I've machined.
http://www.pbase.com/dennygraham/image/161889589/large
I think I might have a hard time taking .010" off the worst
ones though with a 1" diameter wheel. And I would have some
doubts about how flat it would make them. But, your right, I
think they would be good for finishing.

dg

Cratex comes in about 3 different grits- - - -I believe the brown ones are coarse, gray is medium, and white ones do the mirror polish I like on trigger sears with the letoff weight measured in ounces on target rifle triggers. For a little more aggressive rough-out try the Roloc abrasive discs in 1 1/2" diameter that twist onto the flat rubber backing discs. They're available in the 1/4" shank diameter that fits the die grinder collet.
Jerry

When I took my 53 235 engine to the machine shop to be bored, etc, I brought along the cam to get his opinion on it. He pointed at the points of the lobes. There was heavier wear (looked minor to me) on one side of each lobe. He said that this area was originally ground higher than the other side to cause the lifters to spin. Made me scratch my head. What say you?

Next time bring along a wheelbarrow- - - -what he's spreading around will make your garden grow nicely next spring!
Jerry

Here is Greg's diagram.

I deleted my foolishness.

I e-mailed Denny a page from a 79 Iskenderian Cam catalog and it has a page showing both the convex lifter face and the 1 degree taper on the lobes to make the lifters spin. They exaggerate it in the drawings but actually give the 1 degree offset/convex,

Denny, I am assuming you are talking about losing a bid on eBay. I have been using this site for bidding for over 10 years.

http://www.esnipe.com/

It keeps me out of bidding wars and then places a bid 6 seconds before the end of the bidding which doesn't give other bidders time to bid against me. If it is an item that I really want, I usually bid the opening bid to keep the seller from removing the item. My esnipe bid then bids the maximum I am willing to pay 6 seconds before the end.

Denny,

Go to the GM Heritage Center and look at 1935 Master Cars...I know it's a 206, but they do show the convexed lifter with dimensions, I bet the convex it the same for the later engines (why re-invent the wheel). It's way down on web page 86 I think...

Mike B

Mike B., Nice find . Here's a pic of page 86.

@photobucket

http://i669.photobucket.com/albums/...ve_Chevrolet_1935-Chevro_zps8ieemvxy.png

If they're only supposed to make local contact:
1. why are the tappets so strongly offset from the lobe center?
2. why are the tappets so big?

Panic,

Tappet diameter is determined by the maximum valve lift velocity, if the velocity is too high, the cam will overrun the tappet face. The illustrations posted by Tim and Greg show the lobe "elevation view" of the situation, but the velocity portion is best considered as the lobe reaching in and out of the page. Think of what the cam and tappet look like if you could view them along the camshaft instead of beside it. Most automotive applications have settled on a few 'standard' diameters since most engines performed well with the velocities those allowed.

The best reference for this is a book by an oldtimer named Mike Turkish. He worked for Eaton Corporation's Valve and Lifter division back in the 1940's 1950's. I have a copy of his book somewhere deep in my files. If I can lay hands on it, I'll post some background.

Interesting topic.

Tappet diameter is determined by the maximum valve lift velocity

and the lift velocity of those engines is very, very low. This leaves us without a reason...

Nope Ken, didn't lose the bid, fact is, I missed it completely.
I was working in the barn when the alarm in the house went
off. I’ve heard of esnipe but never used it. I usually snipe
it myself in the last 10 seconds. I'll have to keep that in
mind.

Ok. I've already talked to George and Dave about this but for
the record,
1) Isky’s catalog is addressing their cams and cams that
are similar to their cams, not all cams and lifters.
2) The 261 lifters, which are in the '59 engine I have
here are flat. If you know anything at all about inspection
you can see in the pictures of them being checked on a black
granite inspection plate, that their faces check out perfectly
flat and perpendicular to the sides on the NOS GM early lifters
and on the later stock two piece lifters. A 60 inch radius on
a 2.315” by .989” lifter would give you a .002 crown, which
would rock like your grannie’s bent wood rocker. I haven’t
been able to find a NOS GM cam but I’ve got a reground
3836484 cam coming. If it’s been ground to the original
specs then I should be able to see the taper.
Thanks to George, I've got some NOS 5231880 lifters coming
which are the factory replacement for the discontinued two
piece 5231445 lifter. I'll add the pictures of those flat faces
to my album if any one cares to see it.
More documentation.
http://www.pbase.com/dennygraham/261_solid_lifter

Like to see that data if you find that book BD.

And Mime, that is obviously true and documented for 1935 but
not true for 20 years later.

This simple thread is starting to look like the "Never ending story."
One of our longtime 'bolters turned me on to an interesting
site. I'm new to it so I don't know much about it, other
than It's loaded with info about the application and cross
reference to aftermarket replacements, in this case, it's
the GM 5231880 lifter.
The thing that set me back on my heels was their application
listing for this tappet. According to the list it was used
all the way up to 1974 in many Chevrolet and GMC engines.
Which to me means they should be quite plentiful.
At fairly great expense, I'm managed to scarf up a set of
GM NOS 880 lifters.
What this also tells me, is that GM used a flat face tappet
in a whole bunch of their engines, way to many to list here.

I'm definitely going to book mark this site. So I'll pass
the link on to anyone who might be interested in fact
finding and tying up loose ends as I am.
http://www.yoyopart.com/oem/12510095/gm-5231880.html#interchange

Thanks George.
Denny Graham
Sandwich, IL

Sometimes, something just has to be said:
NOS 5231880 paper weights
I'd be ashamed to put these up for sale for anything other
than the cost of shipping, which even then, they'd be over
priced.
Denny Graham
Sandwich, IL

Stovebolt inlines and GMC V6's- - - - -they're still 40-something years obsolete.
Jerry

So are model-T's, A's, Packards, but they're still collectible
and hold some people's interest.

dg