Lancia Motor Club

I have just done a cylinder head compression test and don't know what to make of the results.
All 4 cylinders give a reading of around 90 psi which I believe to be quite low - 140 psi should be achieved
with a compression ratio of 8:1 according to the instructions that came with the tester.
I think the Appia engine is rated at 7.8 so I appear to be at least 40 or 50 psi down.

I intended to do a top end overhaul sometime soon but perhaps it needs more than that?

Hopefully someone will say 90 psi is fine, don't worry about it ....... :)  ???

When I've got a few minutes I will pop a plug out and test mine

seems OK to me I had 0,0,0 and 50psi. problem was the rings sticking in the piston grooves and one broken top ring

Based on those results mine is positively brilliant....... :)

My engine man mumbled something about having the block rebored and the pistons on the conrods by Friday we will see..when it is all back together we will see what a new engine compression should be
Clarkey

90 psi is very good on the  Appia and should be uniform on all 4 cylinders, Andrea

That's good news - many thanks for the info Andrea.

Checked mine yesterday - 105 psi

Many thanks Simon.
Did you do much to the engine that would have improved the compression during the recent extensive restoration of your Appia?
I am now wondering if just a top end overhaul would make any significant difference.

Slight change of subject .......
Since buying my Appia I have been using a lead substitute additive in the fuel because the guy I bought it from said he always had, even though he was unsure if it needed it. So if I do remove the head should the valve seats be changed?

Re engine work, all I did was replace the rings - the bores and pistons had some wear, but within tolerances and I wanted to keep the cost down

The rest of the work was on the bottom end

However, the engine does smoke quite a lot due to valve guide wear, so that is next on my list - I have a new head with new guides and stem seals ready to fit. I did change the valve seats as well so I don't plan to use a lead substitute

I have not been using a substitute in my current engine, because I had always planned to change the head, so it will be interesting to see if there has been any seat damage in the 3,000 kms since it went back together

Hi Guys,
If I could add my two pennorth of years of engine building, a compression test alone is not conclusive, it only tells you how efficient the engine is acting as a pump but not what the problem is. You then need to carry out a cylinder leakage test. This will determine where the losses are, inlet or exhaust valves, piston rings or head gasket. Obviously not many people possess the tester, but worth borrowing/ hiring one before stripping the engine. At least you`ll know it`s possibly just in the head and not tear the bottom end apart unnecessarily. Also as you know, a cold engine will give lower readings due to oil drainage from rings. If the leakage test suggests worn rings, a few squirts of oil down the spark plug holes will temporarily seal the rings and a retest will maybe confirm a valve seating problem. I hope I`m not preaching to the converted.

Thanks Jaydub, all info gratefully received.
My compression test was carried out on a warm engine and in a strange way I was hoping for No 1 cylinder to show
a lower reading than the other 3. The reason being that I suspected those valve stem guides were worn because of the fairly regular occurrence of a misfire and an oiled up plug.
Perhaps the loss of compression due to worn valve guides is minimal and would not show up with a basic (i.e. cheap)compression tester?

I would suggest that valve guide wear leads to oil consumption and perhaps smoke but not loss of compression.

I think 90psi is fine especially if all cylinders are the same. If it was mine I would leave well alone,assuming your oil consumption is not excessive.

In simple terms 110psi is the theoretical max for 7.8 to 1 compression ratio although it will depend on the design valve overlap and the cranking speed I would imagine.

Thanks Ben
Oil consumption is not at all excessive so for the time being I will monitor the situation and leave things as they are.
 

Some other tests you could do is determine if the oil is being burnt on the over run (worn inlet valve guides) or on acceleration (worn pistons/rings).

Am I right in thinking worn valve guides give white smoke whereas worn piston rings give a darker, grey, smoke?

Hmmmm ....more interesting points to investigate. Close observation of exhaust fumes is next on the list.  :)

The most recent compression readings for the carefully built 5th Series engine in my 3rd Series B20 (which has standard pistons and lightly skimmed heads - i.e not high compression) are 172,164,169,165,170,168 with all readings taken at starter cranking speed.
I have a spare race engine which has high comp pistons and more heavily skimmed heads so at some stage I will try to get some readings from that as well as from a standard run in Aurelia engine in another car.
Chris

Chris, I would hate to turn that one over by hand .....

Update......
After a recent long run the small amount of exhaust smoke was black, at tick over speed. I adjusted the carb mixture screw
and there was  a noticeable increase in engine speed so adjusted the idle speed screw as well.
Now no noticeable smoke from the exhaust at tick over but when the throttle is depressed there is some blackish smoke evident.
Assumption now is that perhaps the valve guides are not a serious problem and the likely culprit is piston rings being slightly worn.
Oil consumption is negligible so will leave well alone for the time being I think.

Sounds like things aren`t so bad John. You will usually get black smoke when you press the accelerator after idling because older engines tend to have less well  designed combustion chambers and do not burn all the fuel mixture efficiently and the richer mixtures created under acceleration tend to exit the exhaust system unburnt. Plus of course possibly worn jets, incorrect float levels, ignition timing and valve clearances. You cannot successfully tune the carb without first ensuring all those things are correct.
As a rule, white smoke is water related eg. Head Gasket problems. Blue smoke is oil related. Worn guides will show up if you back off the throttle when slowing down, the ensuing high depression created in the combustion chambers will suck oil down worn guides. Also on start up after standing awhile and oil has run down the guides.
Black smoke is rich fuel mixture created by the things mentioned earlier.
All the best
John

Thanks for your informative reply, valve clearances have been checked and are correct.
I think a carb overhaul will now be next on the list.

check out this site for carb overhaul kits
http://stores.ebay.co.uk/alfa1750scarburetorspartsstore/

clarkey

Excellent, will order one now.  :)

Update.......
Kit ordered and delivered quickly, good service from this eBay seller, they also gave me a rebate on the stated delivery cost because it was being sent from Italy and also delivered to Italy.
The carb has now been stripped and rebuilt with the new kit, first impression is positive - only driven 10 km but definitely seems better to drive now. A longer drive required now and then check plugs and exhaust fumes etc.

Sounds promising John. I like the Al Fresco sun lounger with a Lancia as a sun shade, but I doubt it would have the same appeal in the UK!

John.