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Valve Shims

PostPosted: Sat Jun 15, 2019 8:08 pm
by Melcher Roger
For shimming the exhaust Valves on a rebuild head i need Shims around 3,76-4,06 mm .
I have a Saab Shimming Set under the hand but thicknesses are going to 2,8mm only .
Is it Possible and Safe to use 2 shims per Valve on the right measure to obtain the correct clearance wich is possible with the Saab Kit.
The Upper Shim sits correct in the Collet
Good or Bad Idea ?

Thanks a Lot


Re: Valve Shims

PostPosted: Sat Jun 15, 2019 11:35 pm
by Hawksfield

NO NO :evil:

Re: Valve Shims

PostPosted: Sun Jun 16, 2019 12:58 am
by Chrispy
I wouldn't risk it. The correct shims are pretty cheap from Burton.

Re: Valve Shims

PostPosted: Sun Jun 16, 2019 6:05 am
by UAB807F
I wouldn't risk it either. In theory it should work and I'd have no problem in using 2 shims to confirm the required sizes, but given that the correct size one piece shims are around then I'd buy single shims.

A year or so back I found a batch of shims on Ebay for very little money, I think they were Rover parts rather than Lotus/Ford/Hillman Imp. I bought them because they had a good spread of larger sizes, IIRC there wasn't much below 100 thou. and most were 120+.

That might be an option if you need something larger than the normal range, although I'd expect Burton/QED to have everything you need.

Re: Valve Shims

PostPosted: Sun Jun 16, 2019 9:48 am
by TeeJay
In my opinion, Do NOT use 2 shims.

If you look at the details below, you can see that in the Spring Retainer, the shim drops into it and is retained by it. If you use 2 shims, there is a strong possibility that the top shim will not be retained and float around inside the Follower (bucket).

Valve spring retainer.pdf
(75.96 KiB) Downloaded 60 times

Re: Valve Shims

PostPosted: Sun Jun 16, 2019 6:56 pm
by Melcher Roger
Dear Gents .
Claer statements in your your honest opinions .
I will follow your advices .
Will order at QED the correct shims
It was a a time saving idea only to avoid waiting.....for the right parts .......

Thanks a lot


Re: Valve Shims

PostPosted: Sun Jun 16, 2019 8:45 pm
by rgh0
I would also be wary of needing shims that thick as it indicates the top of the valve stem is lower than desirable and potentially the spring loads have been increased and clearances reduced excessively if the valve is too low in the head


Re: Valve Shims

PostPosted: Mon Jun 17, 2019 9:54 pm
by Melcher Roger
Hello again

I agree with the No Go of using 2 shims per Valve
The Machine shop where the Head was rebuild has worked on the followings:

Inlets New Valves and Valve Seats
Inlets : New Bronze Valve Guides
Outlets : New Bronze Valve Guides , Lapping the existing Valve Seats
Plain Machining Head Surface
Crack and Pressure Testing
Cam Followers done new

The Head PartNr : LP 3215 was never in use since i owned it .
It was from of a complete Spare Part Twin Cam Engine i Purchased in bits togheter with the Lotus Cortina i restored in 2014
The LB Bloc is now done with Liners , New std bore Pistons, Lip Seal Crank etc
The goal is to build a Road / Lip Seal Spare Engine and put it in the 66' Cortina
(Rope Seal number one is still going strong despite his oil consumption with steel Valve Guides and rope seal pissing :-) )

Here is what i measured for a 0,25mm clearance on the EX Side with a new QED 360 Camshaft

1: 4,33mm / 0,170"
2: 4.02mm /0,158"
3: 4,04mm/0,159"
4: 4,03mm/0,159"

Inlets with 0,15mm clearance and QED 360

1, 1,73mm/0,068"
2: 2,09mm/0,082"
3: 1,70mm/0,067"
4: 1,58mm/0,062"

Strange to see the Inlets on the minimum scale and the Exhausts on the higher Scale of the Shims

Shim Sham Shimmy :-)
Thanks and Greetings from Luxembourg


Re: Valve Shims

PostPosted: Tue Jun 18, 2019 10:35 am
by rgh0
Hi Roger

If the head has been redone as described then I would definitely be questioning what is happening in terms of valve length and valve seating locations to get the large clearance between the valve stem tip and cam base circle on the exhaust and small on the inlet .

With the correct length valves seated at the correct location in the head ( to get the correct spring install height) and standard cam followers and standard cam base circle you should end up with shims around 2.8 to 3 mm thick.

You're exhaust shims are 1 mm to thick and you inlets about 1 mm to thin. Why that is the case is not clear but in a newly rebuild and nominally standard head I would be wanting to under the reason so I could understand the short and long term implications.

All the potential dimension variables on both the inlet and exhaust setup need to be examined to determine which are not standard. I you head machinist cannot tell you that immediately and why they did it the way they have then I would look for a new head machine shop.

You can run the head with these shim dimensions..... maybe..... but you may have a variety of problems such as clearance problems on startup or long term problems with excessive wear or fatigue of over stressed springs. It all depends on the cause of the need for these shim thicknesses


Re: Valve Shims

PostPosted: Tue Jun 18, 2019 2:46 pm
by nmauduit
fwiw QED (no afiliation) offers valve shims from 60 to 220 thous...

now to investigate why is there a discrepency inlet vs exhaust, as Rohan pointed out checking the specs of the camshafts may give a clue (are they reground? or only one maybe?), then since apparently exhaust valves and seats were kept (I would have used fresh exhaust valves at that point, for a few extra tenners) then a bit extra clearance comes from there on the exhaust side (also old valves may be of a different height).
Also, are all cam buckets of the same specs (there are thin and thick versions of the followers, though usually one does not mix)?

I'm assuming that the machine shop did a complete job and made sure the installed heights were at the proper resting pressure for each springs, using shims as required - maybe a quick check on that would help to rest assured and sleep well (checking inlet/exhaust the free length / resting height of the springs is not difficult - then if this looks funny, like there is a big difference between sides, take the time to make the calculation of compressed pressure and free gap at full height per spring to make sure the build is actually within specs).
It could be that the discrepency comes from cam base circle and valve length differences.

Re: Valve Shims

PostPosted: Tue Jun 18, 2019 8:01 pm
by Melcher Roger
As I mentioned the goal is to build a realible road engine and use it for longer journeys .
Realibility is much more important to me than searching the last quench of power .
I'll do that with my Lotus Cortina on several jouneys to England /France /Germany /Belgium.
1800 km in 5 days without trouble , driving from full to empty without sitting on eggs

So i will take the head off and bring it to the shop to solve the questions of Valve Lenght /Spring compression/Valve seat depht .
My Engine Shop is helpful and trustfull , no worries for me in that direction .
They are also specialised in Oldtimer running gear and holding her company since 1918 (!) in the same Familiy

Thank you very much for your kind help
Will Post News as soon as i have them .