Valve clearances

[steveww]

Just putting the head back together after various machine work. I put
the shims back in followed by the cams. I was going to measure the new
clearances to work out which new shims I need. Alas there is no
clearance on some of the valves. Any ideas where I go from here? Not
sure what I should do about new shims.


Thanks.

[memini55]

Steve,
When I had the head done on my Europa the machinest took the clearance off
the end of the valve stem to get them back in the ballpark. Then we worked
with the shims to get the exact settings.
Not sure if that is the best way but it worked well for us.

Mark Doubet
66S2

[nebogipfel]

--- In ***@***.***, "stevew_w" <stevew@s...> wrote:



Hi Steve,

I've just done mine so it's fairly fresh in my head. If you measure
your shims assuming you are OK with a micrometer and you are lucky you
will have some shims thinner than the others? It is a bit laborious
but if at least one of your shims is thin enough to give you a
clearance on all the valves then you can easily calculate the correct
sizes by using the thin shim as a measuring shim in all of them.

Failing that you need to beg or borrow some thinner shims to enable
you to get measurable clearances. if your thinnest shim is perhaps
95thou I would go down to about 80-85 and you will almost certainly
have measurable clearances I managed to borrow 4 thin ones to get my
measurements.

I think I read somewhere that it is not advised to use shims less than
80thou (my thinnest is 79).

Sue Miller has a large selection of shims and I'm sure she would post
some to you if you cannot get them locally. I know they are the same
as Hillman Imp and I have been told they are also Rover SD1 but the
Rover shims do not tend to be thin enough.

Another thought .....If you know someone locally with a surface
grinder you could get acouple of shims machined to use as measuring
shims.

Sorry this is a bit wordy I hope it makes sense

John

[nebogipfel]

--- In ***@***.***, "stevew_w" <stevew@s...> wrote:

I forgot to say Mark is right if you cannot get sensible clearances
with a reasonable thickness shim then the next step would be getting a
few thou ground off the valve stems.

As I understand it if the shims are too thin they may split. I suspect
they would have to be pretty thin for that to happen .......unless of
course anyone knows better )

John

[richboyd]

Steve,

It sounds like you put the original shims back in their original location,
without moving the shims around in various combinations. Correct? If so,
your first effort should be swapping shims around.

Try placing the thinnest shims you own (from other cam lobes?) under the
lobes with no clearance. If you gain some clearance (any measurable gap),
great - you can work from there in determining what new shims you need. If
even your thinnest shims yield zero gap, you have two choices: buy even
thinner shims (and hope they open up a gap) or machine the valve stems (as
others have suggested). I would try purchasing thinner shims first (cheaper
and easier than taking head apart to machine stems).

Rich Boyd


At 11:14 AM 1/3/2005, you wrote:

[lotuselan2]

Mark
Your machinist knows his business. He did it the right way first
time. He would have had a good idea how much deeper valves might sit
if he was just facing valves and seats. You avoided thing shims.
Ken
+2 with BDR

[twincamracing]

Pull all your shims and measure them with a micrometer, record the last
two digits of the measurement on the top of the shim with a fine tipped
marker. Sort out the 4 thinnest and do one cam at a time.

Make a chart so you can see which shim is where, check your clearances
and record them, now you can calculate what you need. Shims can be
switched around to reduce the number you may need to purchase.

If the clearance is close and the shim too thick you can dress the shim
on some sandpaper laid on a piece of glass using a solvent or light oil
for lubrication. Move the shim in a figure 8 pattern...It could get
tedious but if you only need a thousanth or two it works great.

If you are in dire straits you can dress a shim down using the side of
a fine grinding wheel mounted on a bench grinder, make certain you have
a way to hold it (junk valve laying about) and a steady rest 90 degrees
to the face. Just a touch or two then the sandpaper on the glass trick
to smooth it and use this to do your initial clearance check.

If the valves were ever done previously you may already have thin
shims. In this event you will need to remove the valves and have the
tips dressed a bit.

Cheers,
Scott



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[rgh0]

A bit of general advice on solving cam clearance shimming problems.
There a lots of ways to do it but most are hacks that cause future
problems.

1. The right way to do it is to have a machinist capable of setting
up the valves at the right height in the head and replacing the valve
seats if necessary. If you dont have a capable machinist then at
least find someone who can measure up a head properly and tell your
machinist what to do. Then with the valves in the right location you
can get the springs and shims within the right tolerance. Anything
else is starting down a road of long term problems.

2. Assuming the valves are not too deep in the head and the rest of
your valve train is standard then you can go down to about 1.5 mm (
60 thou of inch) minimum shim thickness to get the operating
clearance. The shims are case hardened so if grinding down thicker
shims grind only one surface and ensure that surface is faceup
contacting the bucket follower other the valve stem will produce
a "dent" in the shim. Thinner shims than 1.5 mm have 2 potential
problems depending on exact details of the rest of your valve train
components as I have listed below. The shims themselves were used by
most british designed OHC engines of the era eg Imp, Jag, TR7, SAAB.
If your serious about setting up your own heads get at least one
1.5mm shim to enable clearance checking at minimum shim thickness, it
does not have to be useable in an operating engine , just a piece of
1.5mm steel you can use to check clearance to detemine required shim
thickness


The 1.5 mm limit is driven by 2 factors
a. You can get the top of the spring retaining hitting the bucket
follower.
b. You can get the shim fracturing

3. If you are down to minimum shim thickness but dont want to put in
new valve seats. First I would advise against it. You probably have
now got the installed valve spring length to long and replacing valve
seats is actually cheaper than most of the other options anyhow.

4. If you decide to start to modify the rest of your valve gear to
compensate for the wrong valve position the first change I would make
is to go to thinner steel bucket followers rather than grinding the
valve stems. Grinding the valve stems can lead to further problems
with the top of the retainer hitting the bucket.

In the end you have to realise that the valve train components are
designed as a complete package and any modifications must be made
with that in mind and are not wisely done in a piecemeal way to try
to compensate for one problem by creating several more for the next
rebuild ( or the next owner as is generally the case)


regards
Rohan

[Frank Howard]

Steve,

Rohan mentioned SAAB as a possible shim source. SAAB shims on the 99 series
cars are what you need. SAAB 99 owners rarely bring their cars in to dealers
at this point as one hour of shop time can often exceed the value of the
entire car! As a matter of fact, my local SAAB dealer has a higher labor rate for
the older cars. As a result, the dealer should have a wide selection of shims
that are rarely, if ever used anymore. My dealer brought out a big metal box
containing thousands of shims and told me to just help myself as he had
little or no need for them anymore. I took one of each size and when I was done
setting up my valves, I placed the remaining shims in a baby food jar and
covered them with motor oil. Good luck.

Frank Howard
'71 S4 SE
Minnesota

[Lincoln62]

Steve

When I did mine the machine shop/engine rebuilder had a small tin of shims
of the correct diameter. They were mosttly from Morris Marinas (Ital in
England I think, 1500 OHC engine, same as Allegro?). He lent me the tin and
I found small ones that gave me a clearance to measure. He then machined
some thicker ones to the sizes I needed and they were perfect.

It might be worth asking the question, you never know what those guys have.

Peter
66S2
Sydney
--------------------------------------------------------------------
Just putting the head back together after various machine work. I put
the shims back in followed by the cams. I was going to measure the new
clearances to work out which new shims I need. Alas there is no
clearance on some of the valves. Any ideas where I go from here? Not
sure what I should do about new shims.

[Elan45]

Steve,

A long time ago, I had a set of 5/16" washers ground down to .020 or .030" thickness. When starting from scratch on a head I had no history with shim thickness, I put the washers on the studs used to hold the cam caps. Then using some of my thinnest shims on the valves on that cam, I inset the cam and install the caps, but the caps are held a uniform distance away from their normal installed location by the ground washers. If you can't get measurable clearance with the washers in place, then you've got really big problems. Measure the clearance and subtract off the thickness of the ground washers + another thousanth or two for the angle difference since the cap movesvertical and the valve actuation is about 20 degrees IIRC. This would get me close enough to be within a couple fo thousanths when I readjusted the next time w/o the shim washers under the caps. I had done this all earlier by just inserting a feeler gauge under the caps and keeping that gap as consistant as I could, just so the cam was not pulled down fully.

Roger



Just putting the head back together after various machine work. I put
the shims back in followed by the cams. I was going to measure the new
clearances to work out which new shims I need. Alas there is no
clearance on some of the valves. Any ideas where I go from here? Not
sure what I should do about new shims.


Thanks.
























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[foggy]

no experience. what is lash shim in lotus head? My exper. with Alfa.
what's typical lash for typical hot street cam?
who's doing best broad power curve cams these days?

thanks, all
Steve

[Fred Talmadge]

And don't forget the Twin Cam Shim Exchange! The contact is in the Lotus
Ltd monthly publication and probably on their web site as well.

Fred T. '65 S2

[rgh0]

--- In ***@***.***, "foggyalfa" <sfog@o...> wrote:


Steve

8 thou on inlet and 10 thou on exhaust appears to be what most are
designed to.

Lots of good cams available. In UK from Burton, Kent or QED. In USA
from Dave Bean or Elgin. In Australia from Wade or Stenlake. They all
do good quality work as far as I can tell.

Currently I am building an engine using cams from John McCoy at
Omnitech Engineering who does the Stromberg head conversions he has
some very good high lift, low duration profiles that work well with
his high flow converted heads.

In general whats important is to keep a short duration of 280 to 290
degrees while going for as high a lift as you are prepared to spend
money on and match it to a good porting job and good carb and exhaust
mods. Longer durations only really work in high compression race
motors in lightweight open wheelers and even then I dont believe they
are truely optimum.

i.e The classic L1 profile at .41 lift and 300 degrees duration is
not as good as a .44 lift and 280 degrees duration in any engine or
application however .45 lift is harder to get into a head.

More lift means more money for design expertise as it is not simple
fitting in a high lift cam properly, parts supply for new valves,
springs and retainers, buckets, cams etc and machining work to get it
all done right.

More lift and short duration means more aggressive valve acceleration
so quality of components and good assembly and operation becomes more
important to avoid excessivly short life.

Rohan

[steveww]

Thanks for all the great feedback. Yep I just put the old shims back
in the place thay cam from. First off I will measure all the shims I
have and work with the thinest. I have not measured any yet but
looking at them I would say most are about 3mm (118 thou) thick so it
looks like I have plenty of room to play with.