Camshaft replacement, tappets and shims

[davidwinegar]

Hello all,

As I dig more into my engine problems I find more troubles--seems to
be par for a Lotus car.

The latest problem (in supposedly my rebuilt engine from a Lotus
dealer--what a sucker I was)is that I found one tappet in which the
surface was concave, the same camshaft nose on that tappet in bad
condition and some strange loking shims.

My quesitons are can I get a replacement cam shaft for a reasonable
price somewhere? Can I get just one or do I need to buy a set of them
and how can I tell what specs mine are--I believe mine are the
standard b-type accoding to the Wilkins book description, but are
there different specs that I should worry about? Any suggestions
where to find?

Second question is the shims in my car are very strange looking. Mine
are smaller diamter than the hole where they fit and are quite thin
1.75mm or thinner--is this normal? I had heard that the Saab 99 had
the same shims but when I looked at them the thinnest they had was
1.98mm. Can anyone enlighten me on this subject?

Thanks for the help

David
1970 +2S

[gjz30075]

--- In ***@***.***, "david_c_w" <david_c_w@y...> wrote:

David,
You might have a Cosworth setup, due to, perhaps, relatively radical
cam specs and/or springs. I don't know the size offhand but I know
they're smaller than stock.

Greg Z

'72 Sprint

[M100]

On Tue, 28 Jun 2005 13:20:14 -0000, "david_c_w" <***@***.***>
wrote:



The thickness (or lack of it) It sounds like a bodge usually used when
the valve seats are cut back too far. 1.75mm = approx 70 thou I seem
to recall 80 (or 100?) thou being the thinnest recommended. The
diameter reduction sounds strange as well. Is the diameter regular or
does it look like its been on a bench grinder?

Martin

72/45
--

[types26/36]

--- In ***@***.***, "Greg Zelazek" <gjz30075@b...>
wrote:




I think QED,Burtons,Cosworth and some others have "top hat" shims and
are as the name implies(top hat in shape) If your shims are just flat
and a smaller diameter so they are loose in the retainer that cant be
right! the T.C. shims are 5/8" diameter.
I have seen thin small diameter ones fitted in a T.C.and I think they
were from a motorcycle...Kawasaki I think.
Brian
64Elan/72Sprint/J.P.S.Europa/Birkin T.C.Seven

[rgh0]

David

By the sound of it whoever built your engine had no idea what they
were doing or no ethics or both. Hopefully they did not do to much on
the bottom end when they did the cylinder head

Specific responses to your questions

1. Individual Replacement cams are available from lots of sources to
lots of profile grinds. You need to really get your current cams
measured to determine what they are by a cam specialist to ensure you
buy a suitable matching cam you cant rely on the markings as many
cams have been modified by now. Cams lobes can be rebuilt by spray
welding and reginding or just regrinding on a smaller base circle.
Both techniques require some knowledge as they both have other
implications for other engine components so you need to have
knowledge to go down either route from an experienced engine builder
or by asking questions on the forum.

2. Shims at around 70 thou can be workable with careful design of
matching components ( valve tip length, retainer desing, bucket
design) but unless you are building a racing engine design with
limited space for a high lift camshaft they should not be required
and generally indicate valves that are too recessed in the head.
Shims that dont fit in the retainer recess properly just show
ignorance on the part of the engine builder. In general it is
possible with current valve train design and available components to
build a high lift racing design to .500 inch lift without resorting
to excesively thin shims or top hat shims so you should not need them
in a normal road engine.

I would suspect and question just about every component in your
cylinder head from your description of how the valve train has been
set up.
i.e.
Valve seats probably over cut and valves recessed.

The valves have probably also been recut to reclaim and match the
over cut seats and are probably getting to the end of their fatigue
life and you risk droppping a valve head, they will probably have
worn stems also.

The valve guides are probably worn.

The buckets will be worn and bucket sleeves probably worn also.

Springs have probably lost tension.

The retainers and collets may be reusable if your lucky !

Hopefully the cam tunnel bores are straight and you only need to
replace the cam bearings which will probably be worn and letting
excessive oil into the head.

Dont worry most twin cam head I have seen have most of these problems
and all can be fixed.

Rebuilding a Lotus head takes skill and money. The less skill you
have the more money you need to pay someone else who has the skill.
Even if you pay someone else to do the work you need enough knowledge
to ask the right questions which is the benefit of forums like this.


regards
Rohan