Tight valve Clearances on an XUD7 engine

Unread post by **CitroJim** » 02 Dec 2006, 16:17

Junior has stopped driving me up the wall. I have found her problem (I hope!)

For background read the saga here:

http://www.frenchcarforum.co.uk/forum/v ... hp?t=20789

She has very tight valve clearances, especially on the inlet side. The minimum clearanace should be 0.10mm and the tighest (cold) is 0.02mm and the best is 0.075mm.

A re-shim is in order. Before I proceed further please give my proposals a check-over and see that I'm not being silly in my calculations.

1. I'm making an assumption that I should set the clearance to the "loose" end of the tolerance (i.e. 0.25mm on the inlet, 0.40mm on the exhaust). Is that right?

2. I calculate that the new shim thickness is derived thus:

New Shim Thickness = Old Shim Thickness - (Target Clearance - Measured Clearnace)

Putting figures into it: 3.40 (old shim) - (0.25 - 0.075) = 3.225mm (New Shim)

3. Are XUD shims the same as XU (petrol) shims?

4. The best way to obtain replacements? Are they available singly from Pug/Cit dealers or is there a better route to obtaining them?

I have created an Excel Spreadsheet to calculate new shim thicknesses but cannot see any way of uploading it to here. If anyone would like one, please PM me.

Many thanks for all your help

AndersDK · Unread post by **AndersDK** » 02 Dec 2006, 18:36

Hi Jim -

Calculating the new shims is easy.
Gauge the actual clearance, then gauge the shim after removal.
Then select and insert a new shim with a lesser thickness to account for the wanted clearance.

It is of course very important to keep track of which valves and shims goes where. If youy loose track - its double labour

Most garages & dealers would have a selection box of shims to rent exactly for such jobs.
Shims are the same for XU/XUD engine types.

Shims should be gauged with a good quality micrometer gauge.

Unread post by **CitroJim** » 02 Dec 2006, 20:57

Thanks Anders,

Excellent stuff

I shall go ahead now after finding a friendly garage to get the shims from.

First though I have to get a metric micrometer. I have an imperial one but there is no way I'm going to measure any shims in inches and then convert to mm. Too much risk of error for my liking

Unread post by **philhoward** » 03 Dec 2006, 21:37

1mm = 40 thou with a very small error (1.5%)...if you're using Excel, then just apply the 25.4 factor!

Unread post by **CitroJim** » 14 Dec 2006, 13:20

Reshimmed and bingo

Junior had lain for over a week with her top-end in bits and she started with half a turn of the starter after the reshim and settled immediately to a perfect idle.

Jobs a good 'un 8)

It was a lot of fun doing the job and quite easy really. If anyone is interested I'll do a blow-by-blow account of how to do it. I have also refined my Excel shim calculator somewhat so if anyone wants a copy, PM me.

fastandfurryous · Unread post by **fastandfurryous** » 29 Dec 2006, 19:53

citrojim wrote:First though I have to get a metric micrometer. I have an imperial one but there is no way I'm going to measure any shims in inches and then convert to mm. Too much risk of error for my liking

Funny you should say that, as the shims in XU/XUD engines are actually imperial, but sold/specced as metric.

If you grab a selection of XUD shims (I now have dozens of them) and measure them in metric, the intervals don't make sense. Measure them in imperial, and hey presto, they are available in steps of 1 thou'.

I now always work in thou' when shimming an XUD... it's so much easier.

Unread post by **lolingram** » 01 Jan 2007, 02:22

If you grab a selection of XUD shims (I now have dozens of them) and measure them in metric, the intervals don't make sense. Measure them in imperial, and hey presto, they are available in steps of 1 thou'.

I now always work in thou' when shimming an XUD... it's so much easier.
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Is this 'cam in/out' job?

Unread post by **CitroJim** » 01 Jan 2007, 07:48

lolingram wrote:I now always work in thou' when shimming an XUD... it's so much easier.
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Is this 'cam in/out' job?

A cam out job this but not as bad as it sounds. The BoL for once does the task quite well really and if you are careful you don't need to take the cambelt right off. Depending on the model, you can sometimes even escape the task of removing the cam sproket on the camshaft too. I pulled the 205 cam out complete with cam sprocket and PAS/vacuum pup pulley still attached. Main thing is to lock the fuel pump and crankshaft in their timed positions.

I now always work in thou' when shimming an XUD... it's so much easier.

Interesting. I noted they seemed very nominal in metric measure

How strange thay are imperial. This lends a bit of credence to the legend that the XUD engine was designed, in part at least, by Ricardo, the British firm famous for the Ricardo Comet combustion chamber. The XUD has such a combustion chamber in very classical form.

Unread post by **lolingram** » 01 Jan 2007, 08:30

A cam out job this but not as bad as it sounds. The BoL for once does the task quite well really and if you are careful you don't need to take the cambelt right off. Depending on the model, you can sometimes even escape the task of removing the cam sproket on the camshaft too. I pulled the 205 cam out complete with cam sprocket and PAS/vacuum pup pulley still attached. Main thing is to lock the fuel pump and crankshaft in their timed positions.

Quote:
I now always work in thou' when shimming an XUD... it's so much easier.

-------------------

Interesting. I noted they seemed very nominal in metric measure How strange thay are imperial. This lends a bit of credence to the legend that the XUD engine was designed, in part at least, by Ricardo, the British firm famous for the Ricardo Comet combustion chamber. The XUD has such a combustion chamber in very classical form.

------------------

If you care to read Harry Riccardo's 'The High Speed Internal Combustion Engine', it might be less of a surprise... he is the king of modern small diesel engines (until of course CR reared its sometimes ugly head).

Well worth seeking out a late edition IMHO - lots of info on Merlins as well as the Crecy.