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Mick Matheson
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Username: mick_matheson

Post Number: 1
Registered: 9-2014
Posted on Tuesday, 05 May, 2015 - 06:17 pm:   Edit PostDelete PostView Post/Check IP

I'm in the process of estimating the condition of the engine in 193 RY, a 1934 P II. The compression seems fairly consistent across all cylinders, but does anyone know what the optimum compression should be when measured in psi (or any other unit I can convert from)?

Many thanks.
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bob uk
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Posted From: 94.197.121.177
Posted on Wednesday, 06 May, 2015 - 08:50 am:   Edit PostDelete PostView Post/Check IP

Consistent readings within 5% to 10% are a good sign of heathlty compression.

I dont know what the actual figure is but if we assume 4 to 1 CR then thats 60psi plus say 10 psi due to valve overlap pumping the cylinder up.

So at a not so wild guess 70psi.
1 atmosphere is 14.7psi. Multiply by CR then add for overlap.

A camera in the spark plug hole is useful.

I am green with envy a Phantom 2 is a lovely old Roller. Bits are expensive but easy to work on.
They go well, they sort of gather speed in top gear from 10mph, happy to cruise at 70.

Back to compression. I have tested many cylinders and I have yet to find an engine that has miles on it where the figures are exactly right according to the book.

It all about consistency. I believe that like most engine makers RR dont give a figure because customets may get worried when their car fails to exactly match.

The pressure test is a bit flawed because the best way to check is by power balance. This is easy. Short out each cylinder in turn and note the rev drop. If all the tev drops are the same then the engine runs very smooth. This way the test is more dynamic. It does it on a running engine which is what counts.

When evaluating engines I like to reset things to see if the engines does as expected. Does a mixture screw actually work.

This habit caused a customer to blow steam. He asked me to check out a XJ6 with a rough engine. Whilst checking I released the stuck on autochoke. And of course the engine started to run nice. The seller of the car then decided since the car was now fixed and he watched what I did to get the choke, he would keep the car. My client was livid because he lost out on a nice jag at a bargin price due to rough running. Whoops. On the other hand it would have been dishonest to rip off the seller for a stuck choke, its a known jag fault.

(Message approved by david_gore)
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Mick Matheson
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Username: mick_matheson

Post Number: 2
Registered: 9-2014
Posted on Saturday, 16 May, 2015 - 06:18 pm:   Edit PostDelete PostView Post/Check IP

Thanks, Bob. Your insights are greatly appreciated. The readings I'm getting when cranking the engine are around 60psi. The claimed compression ratio is 5.28:1 but I have no idea what the combustion chamber volume is, so can't calculate a theoretical pressure. But as you say, if they're consistent, that's a good sign. The engine runs pretty roughly, a problem I haven't yet delved into, but it seemed to have plenty of power when it was running nicely.

I'll give your rev-drop test a go. It might be a while till you hear back - I have another car to service, another to put back on the road and a long list of chores to get done before I can return to the Phantom.

Thanks again.

Cheers,
Mick
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Bob UK
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Posted From: 188.29.164.55
Posted on Sunday, 17 May, 2015 - 06:44 am:   Edit PostDelete PostView Post/Check IP

Plenty of power is a good sign obviously. Rough running on idle. Just do the usually stuff and it should go.

Many moons ago I fixed a Vauxhall Cresta that idled roughly. The carb hot spot was burnt through and exhaust gases were mixing with the inlet stuff the hole was quite small, and the car drove fine but idled bad.

Just so you are aware that this can happen.

(Message approved by david_gore)
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Mick Matheson
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Username: mick_matheson

Post Number: 3
Registered: 9-2014
Posted on Tuesday, 09 June, 2015 - 01:20 pm:   Edit PostDelete PostView Post/Check IP

Just an update for anyone interested. Rather than look for the major issues I'd inferred were present, I've gone back to basics. Never a bad thing to do, is it?

I'd already done the valve clearances. At the time I'd fitted new plugs and set the gap at 30 thou as advised by someone else, but this time I re-set them to 20 thou as per the book. Suddenly the Phantom ran almost perfectly. Lots of power.

However, it idled a little roughly, showed signs as leanness when snapping open the throttle, and had a hint of hesitation under load such as long hills. Checked the float level and found it was low. It seems to me this float set-up is not easily adjustable (RY series car) but yesterday afternoon my neighbour announced he'd bought a small lathe. As the car's float needle has a pronounced groove worn into it, I think I'll give him an excuse to play with his new toy by turning up a new, shorter needle for me. I'm sure he'll jump at the chance.

At least by then I hope to have the Phantom running nicely. This still leaves the question of whether the engine is worn or not, but for now the only obvious signs of anything series being wrong are one very, very noisy valve and a couple that are a bit noisy.
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Geoff Wootton
Grand Master
Username: dounraey

Post Number: 751
Registered: 5-2012
Posted on Tuesday, 09 June, 2015 - 01:24 pm:   Edit PostDelete PostView Post/Check IP

Mick

If you get a chance, it would be great to see some pics of your P II.

Geoff
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Mick Matheson
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Username: mick_matheson

Post Number: 4
Registered: 9-2014
Posted on Tuesday, 09 June, 2015 - 05:58 pm:   Edit PostDelete PostView Post/Check IP

Hi Geoff, I'll get some pics next time it's out of the shed. It belongs to my father, John, who has had it out with the club a few times.
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Geoff Wootton
Grand Master
Username: dounraey

Post Number: 752
Registered: 5-2012
Posted on Wednesday, 10 June, 2015 - 12:19 am:   Edit PostDelete PostView Post/Check IP

Hi Mick

I look forward to them.

Geoff.
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Mick Matheson
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Username: mick_matheson

Post Number: 5
Registered: 9-2014
Posted on Monday, 22 June, 2015 - 04:11 pm:   Edit PostDelete PostView Post/Check IP

Hi Geoff, took the PII out to re-register it today and snapped a photo. Still haven't got the carb properly tuned but it's close.
PII Barker Sedanca Deville
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Geoff Wootton
Grand Master
Username: dounraey

Post Number: 786
Registered: 5-2012
Posted on Tuesday, 23 June, 2015 - 12:38 am:   Edit PostDelete PostView Post/Check IP

Mick

Superb.

I can only imagine the interest your car attracts whenever you take it out.

Geoff
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Randy Roberson
Grand Master
Username: wascator

Post Number: 458
Registered: 5-2009
Posted on Tuesday, 23 June, 2015 - 01:13 am:   Edit PostDelete PostView Post/Check IP

Hey, it's a beauty!
sort of Goldfingerish, also, although that was a III.

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