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Valve clearances - Larger than 150 shim - what to do?

PostPosted: Mon Feb 28, 2005 9:23 am
by "bridgitwilliams&quo
Hello,
I've had some inlet valves made, and after a stuff up with them being
too long, they are now too short.

To work the proper clearances I've doubled up some shims and get:
1 215 thou
2 192 thou
3 183 thou
4 201 thou

So the shims are about 1.5mm (60 thou) larger than the largest lotus
shim of 150.
Will I run into trouble getting some special shims made - or should I
start again and have the valves remade to the proper length, and match
them to the cut seats (they are about .5mm larger than the big values)

Thanks
Rhys

Valve clearances - Larger than 150 shim - what to do?

PostPosted: Mon Feb 28, 2005 10:36 am
by lotuselanman
Gidday Rhys,
Sounds like a bit of a Dunkirk job but not to worry. Shims can be made froma high tensile bolt. Get the shims cut as close as practical to you requirements have them finished on a surface grinder. Any good Engine / Machine shop should be able to help you.
See ya, Les
----- Original Message -----
From: bridgitwilliams
To: ***@***.***
Sent: Monday, February 28, 2005 7:22 PM
Subject: [LotusElan.net] Valve clearances - Larger than 150 shim - what to do?



Hello,
I've had some inlet valves made, and after a stuff up with them being
too long, they are now too short.

To work the proper clearances I've doubled up some shims and get:
1 215 thou
2 192 thou
3 183 thou
4 201 thou

So the shims are about 1.5mm (60 thou) larger than the largest lotus
shim of 150.
Will I run into trouble getting some special shims made - or should I
start again and have the valves remade to the proper length, and match
them to the cut seats (they are about .5mm larger than the big values)

Thanks
Rhys









To search the mailing list archives:
http://www.escribe.com/automotive/europ ... index.html

Valve clearances - Larger than 150 shim - what to do?

PostPosted: Mon Feb 28, 2005 12:01 pm
by garyeanderson
Hi Rhys
Cosworth BDA type shims are available in sizes up to .200 inch, but
that still leaves you with one valve that needs a custom shim.
Burtons and Dave Bean carry them.

Gary

--- In ***@***.***, "bridgitwilliams" <[email protected]> wrote:

Hello,
I've had some inlet valves made, and after a stuff up with them
being

too long, they are now too short.

To work the proper clearances I've doubled up some shims and get:
1 215 thou
2 192 thou
3 183 thou
4 201 thou

So the shims are about 1.5mm (60 thou) larger than the largest lotus
shim of 150.
Will I run into trouble getting some special shims made - or should
I

start again and have the valves remade to the proper length, and
match

them to the cut seats (they are about .5mm larger than the big
values)


Thanks
Rhys

Valve clearances - Larger than 150 shim - what to do?

PostPosted: Tue Mar 01, 2005 9:32 am
by rgh0
Rhys

Before deciding on thicker shims or longer valves you need to check
that the rest of the valve train will still work with the shorter
valves. Your valves are probably around 0.1 inch shorter than normal
which is similar to putting a 0.1 inch higher lift cam on a standard
length valve and this normally requires special design to get it all
to work.

You need to check

1. Spring load installed and at full lift. This will be higher than
orginal with the shorter valves. You need to keep installed spring
load around 75 to 85 lbs and keep the full lift load under 200 lbs in
a road engine for acceptable cam and follower life.

2. Clearances at full lift. You need to check for spring binding and
retainer to valve guide clearance at full cam lift as these will have
closed up with the shorter valves.

If you dont know how to do these checks with equipment you have
available then get the help needed as getting it wrong can ruin a
head.

If the valves are not the approx 0.10 inch too short suggested by
your measurements then you also need to check the valve location in
the head as they may be mounted to low.If they are too low you then
have risks around interference with the pistons or between the valves
themselves on overlap. Checking all of this is harder still but
starting point is to know exactly how much shorter the valves are
from standard.


Making or sourcing thicker shims will work OK if all the rest checks
out. If they do not and there is a reasonable chance of this
depending on the rest of your head details then you need to go back
to the standard length longer valves.

Rohan

Valve clearances - Larger than 150 shim - what to do?

PostPosted: Tue Mar 01, 2005 1:41 pm
by "Roger Sieling"
Rhys,

After reading Rohan's suggestions to you and remembering a friend's Europa rebuild and his difficulties with valve clearance ( the machine shop didn'tcut the new valve seats deep enough), I wonder if you aren't suffering from the same sort of problem.

You mentioned that the valves you've had made are about .5mm larger than big values[sic], and I assume you mean big valve. I don't know why you had valves made rather than just buying them off the shelf, but that makes me wonder if you opened the ports and valve seats up to match the larger heads onthe valves? If you didn't do anything to the seats, you will see no performance benefit from the larger valve, and in fact, because they would then protrude into the combustion chamber, and would also shroud the open port more than the proper sized valve, you would actually acheive a lower power than standard. This would also cause the valve to sit lower in the head, requiring the thick shims you have described.

Just as Rohan suggested, you would also be overloading the valve springs causing premature wear on the tappets and cam lobes, and even possible coil bound condition and possible serious damage to the head.

BE CAREFUL!!!!!!!

Roger


>> ***@***.*** 2/28/05 4:22:33 AM >>>


Hello,
I've had some inlet valves made, and after a stuff up with them being
too long, they are now too short.

To work the proper clearances I've doubled up some shims and get:
1 215 thou
2 192 thou
3 183 thou
4 201 thou

So the shims are about 1.5mm (60 thou) larger than the largest lotus
shim of 150.
Will I run into trouble getting some special shims made - or should I
start again and have the valves remade to the proper length, and match
them to the cut seats (they are about .5mm larger than the big values)

Thanks
Rhys










To search the mailing list archives:
http://www.escribe.com/automotive/europ ... index.html



Yahoo! Groups Links










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Valve clearances - Larger than 150 shim - what to do?

PostPosted: Wed Mar 02, 2005 11:16 am
by garyeanderson
Rhys
I was looking through QED's catalog that I picked up at Donington
last March and there is a listing for a "top hat shim" of .220 inch
for 2.50 gbp, grind away .005 and you should be all set. Part numbers
for custom shims over .150 inch is 101xxx where xxx is the shim
thickness. Cost is 3 gbp + VAT each.

Gary

--- In ***@***.***, "garyeanderson"
<[email protected]> wrote:

Hi Rhys
Cosworth BDA type shims are available in sizes up to .200 inch,
but

that still leaves you with one valve that needs a custom shim.
Burtons and Dave Bean carry them.

Gary

--- In ***@***.***, "bridgitwilliams" <[email protected]> wrote:
>
> Hello,
> I've had some inlet valves made, and after a stuff up with them
being
> too long, they are now too short.
>
> To work the proper clearances I've doubled up some shims and get:
> 1 215 thou
> 2 192 thou
> 3 183 thou
> 4 201 thou
>
> So the shims are about 1.5mm (60 thou) larger than the largest
lotus

> shim of 150.
> Will I run into trouble getting some special shims made - or
should

I
> start again and have the valves remade to the proper length, and
match
> them to the cut seats (they are about .5mm larger than the big
values)
>
> Thanks
> Rhys

Valve clearances - Larger than 150 shim - what to do?

PostPosted: Thu Mar 03, 2005 9:21 am
by rgh0
Top hat style versus flat disk shims are normally only used on racing
engines with high lift valve setups and different style spring
retainers. Dont know why they offer them in such big thicknesses for
a twin cam as the problem with a race engine valve setup is normally
fitting it all in and ending up to very thin shims. maybe its just
because they are made for cosworth engine which are desinged to run
with a thicker shim ?

If you use top hat shims on a normal twincam to getthe extra
thickness you need to ensure no interference with the retainers being
used and also that extra thickness needed is not due to other
problems or will cause other problems in the engine as I previously
discussed.

Rohan

Valve clearances - Larger than 150 shim - what to do?

PostPosted: Thu Mar 03, 2005 12:13 pm
by "Sean Murray"
IMHO, the reason why top hat shims are used instead of the standard disc shims depends on whether the valve stem protrudes above the level of the top of the retainer. If it does, the shim is not sitting in the retainer cup and can slide out sideways, so a cup is then required in the bottom of the shim, making it a "top hat". Just depends on the relative dimensions of the valve, retainer, and cam, rather than the state of tune.

Sean Murray
----- Original Message -----
From: Rohan Hodges
To: ***@***.***
Sent: Thursday, March 03, 2005 9:21 AM
Subject: [LotusElan.net] Re: Valve clearances - Larger than 150 shim - what to do?



Top hat style versus flat disk shims are normally only used on racing
engines with high lift valve setups and different style spring
retainers. Dont know why they offer them in such big thicknesses for
a twin cam as the problem with a race engine valve setup is normally
fitting it all in and ending up to very thin shims. maybe its just
because they are made for cosworth engine which are desinged to run
with a thicker shim ?

If you use top hat shims on a normal twincam to getthe extra
thickness you need to ensure no interference with the retainers being
used and also that extra thickness needed is not due to other
problems or will cause other problems in the engine as I previously
discussed.

Rohan

Valve clearances - Larger than 150 shim - what to do?

PostPosted: Fri Mar 04, 2005 12:42 pm
by rgh0
--- In ***@***.***, "Sean Murray" <[email protected]> wrote:
IMHO, the reason why top hat shims are used instead of the
standard disc shims depends on whether the valve stem protrudes above

the level of the top of the retainer. If it does, the shim is not
sitting in the retainer cup and can slide out sideways, so a cup is
then required in the bottom of the shim, making it a "top hat".
Just depends on the relative dimensions of the valve, retainer, and
cam, rather than the state of tune.

Sean


I agree with you that the basic reason for top hat shims is to
replace disk shims when the retainer will not locate them. However
you only find retainers that do this offered as part of race valves
spring kits. Now this is a bit of a mystery as for race setups you
want the top of the retainer as high as possible to maximise spring
length and this ensures you can naturally locate the normal disk shim
OK. Any normal road setup I have seen does not require top hat shims
from any vendor and any sensible race setup does not need them either.

Thus I dont know why they are offered or used but people like QED
and Dave bean do it.

Rohan

Perhaps its about minimising weight by having a light retainer and
the top hat shim is smaller than and lighter than its disk equivalent
but I dont think this is signficant at any real rpm.