P2 compression

[RobHomewood]

I have been trying to identify the lack of power on my P2 16 engine - it loses power on hills- pretty tedious struggling along in third at 20 mph. As a first step I have done compression testing but cannot find anywhere what compression a healthy engine should produce. I have read that a rule of thumb would be 20X the compression ratio which in the case of a 1947 16 engine would be 6.5 x 20 = 130 PSI. My results were 110, 112, 111, 97, 105, 110. Obviously No 4 looks low but maybe just within tolerance? Retesting with some oil in the bore (wet test) brought it up to 127 PSI which may indicate poor rings I understand. (wet testing No 1 and No 5 for comparison gave 133 and 125 PSI respectively). Trouble is I am not sure whether the other cylinders' compression figures are what should be expected as a baseline. The engine has only done about 13.5k miles since the rebore in 1973 after about 62k previous miles. Does anyone have any comparable data please so I can work out how serious the issue is? If those levels are acceptable then I shall work through timing,ignition,carb etc

[Chris C]

Has this particular problem suddenly become noticeable, or has it crept up on you ??
If it is a sudden problem, then it is unlikely to be an engine compression problem.
However, your figures suggest that it could well be a compression pressure problem.

It is important to first check and reset the valve clearances for your engine. Get the engine up to normal operating temperature, then check the
compression pressures by cranking over the engine, with the carburettor butterfly valve fully open.
A good engine should produce 120 - 130 psi comp pressure (dry test) On a part worn engine you may see up to 3 - 5 psi different between cylinders
Once it gets to more than 6 psi and up to 10+ psi then you are loosing too much pressure via the rings or cyl bores or both.
The difference you have found between a dry and wet test probably means that you have ring or bore wear.
However, it is worth checking the carb, you could possibly have a blocked filter or blocked jet.
Also best to clean and reset the plugs & points, if you haven't already done so.
(above compression figures come from a S1 Land Rover manual)

Hope this info helps you somewhat in getting to the bottom of your current problem.

[luli]

Quite often the issue is`not (only?) the rings and bores, but the valves. There are established methods to distinguish between them. Is your car consuming oil? Is there blue smoke coming out of the muffler? Has the head been modified to use unleaded petrol?
I am using a vacuum gauge which is very efficient in detecting engine problems.
You can see some pictures here: http://wp.me/pXLKy-1r2

[chris dancey]

Sorry if I am a little late with a reply, just come ' on line ' again.

The above replies are valid. I have just overhauled the cylinder head on my '38 coupe. That is lapping the valves, new head gasket and resetting the tappets. The difference is quite marked. I have also an increase in the compression figures from 110-130 on all cylinders, I also ( like Luli ) have a vacuum gauge fitted and have seen a marked increase in the vacuum value.

The problem would suggest that you may have a leaking head gasket / valves need lapping / head bolt tightening ? Head bolts can loosen , especially after engine strip down allowing gases to pass the head gasket..worth checking.

Chris

[RobHomewood]

I have just got back on line and thank you all for your replies.
Chris C- No, the problem is not new I dont think but I have spent nearly a year getting to know this car and am only just addressing this problem. I did warm up the engine before the test and tested with the accelerator fully open but I shall re-test the carburettor. (I have previously cleaned the air filter by soaking in paraffin etc.)
Luli- if I get a vacuum gauge where do I connect it? I have seen it suggested that I may have to drill a hole in the (inlet?) manifold to attach it. Is that the only way? Or would a leak test be equally effective way of identifying piston v. valve fault?
Chris Dancey- the lower figures for cylinders 4 and 5 could indicate a head gasket leak I guess but I have seen no other evidence- no water loss, no white gunge on the oil cap etc. Not sure how else to check this without removing the head. I would like to pin down the basic issue before starting work if I can.
Can you recommend anyone here in the deep south west to re-seat valves etc or should I take the work up country? I dont have the expertise myself and I wouldnt want to risk learning on the job! I am also worried that the piston rings may also be at maximum size in which case is re-sleeving the only viable option?
Thanks again- the advice on this forum is really invaluable.

[luli]

The natural place to take vacuum measurment on a P2 Rover is the manifold outlet to the automatic oiling system. You can disconnect the present tube and replace it with the vacuum meter tube if the connection is temporary, or use a T connector if you want to have it permanently.
See an example here: http://wp.me/pXLKy-sa

[chris dancey]

Yes Luli, I have made this conversion exactly as you describe, it does make the connection very easy....I just wish I could read your text. I can speak English, French and some Greek, but not got around to Urdu ?

Chris

[luli]

Many people "read" the site with the help of google/microsoft translator, which, at least, gives some idea of what is written. I will try to add english captions to the pictures.

[lakesrally]

I enjoy looking at your site luli but I'm sure I'm not the only one whose PC comes back with a message saying that it cannot translate the page for some reason.

[luli]

Have you tried the google chrom browser? It is a no charge software and it translates, sort of.