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Author Topic: S3 Appia compression test  (Read 9096 times)
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John B
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« on: 16 July, 2016, 10:17:41 AM »

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 ....... Smiley  Huh?
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1961 Appia S3
1969 Fiat 850 Special
simonandjuliet
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« Reply #1 on: 16 July, 2016, 10:31:49 AM »

When I've got a few minutes I will pop a plug out and test mine
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Amilcar CGS, Aprilia Cabrio, S2Aprilia, Ardea camioncino, S2 camioncino, S2 furgoncino, R4 Sinpar, R4 Rodeo, 65 Moke, R60 Tractor, R60 S, Toselli 78, Moto Guzzi Ercole, Disco 3, Mini ALL4 JCW, Moto Guzzi Cardellino, Fulvia GT, RE Himalayan, Ypsilon
lancianut666
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Slow but rough


« Reply #2 on: 16 July, 2016, 02:22:48 PM »

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
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Fulvia Coupe S2 Flavia Coupe 1967 1.8 Kugelfischer Prisma 1.6 carb Y10 Fila Y10 Touring Dedra 1.8 Dedra 2.0 Turbo Appia S1
John B
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« Reply #3 on: 16 July, 2016, 04:14:06 PM »

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....... Smiley
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1961 Appia S3
1969 Fiat 850 Special
lancianut666
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Slow but rough


« Reply #4 on: 17 July, 2016, 08:58:50 AM »

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
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Fulvia Coupe S2 Flavia Coupe 1967 1.8 Kugelfischer Prisma 1.6 carb Y10 Fila Y10 Touring Dedra 1.8 Dedra 2.0 Turbo Appia S1
nistri
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« Reply #5 on: 18 July, 2016, 12:51:48 PM »

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

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Fulvia GTE
Fulvia Sport 1.3 S
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John B
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« Reply #6 on: 18 July, 2016, 02:25:36 PM »

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.


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1961 Appia S3
1969 Fiat 850 Special
simonandjuliet
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« Reply #7 on: 19 July, 2016, 08:13:16 AM »

Checked mine yesterday - 105 psi
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Amilcar CGS, Aprilia Cabrio, S2Aprilia, Ardea camioncino, S2 camioncino, S2 furgoncino, R4 Sinpar, R4 Rodeo, 65 Moke, R60 Tractor, R60 S, Toselli 78, Moto Guzzi Ercole, Disco 3, Mini ALL4 JCW, Moto Guzzi Cardellino, Fulvia GT, RE Himalayan, Ypsilon
John B
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« Reply #8 on: 19 July, 2016, 11:44:33 AM »

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?

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1961 Appia S3
1969 Fiat 850 Special
simonandjuliet
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« Reply #9 on: 21 July, 2016, 08:12:45 AM »

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



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Amilcar CGS, Aprilia Cabrio, S2Aprilia, Ardea camioncino, S2 camioncino, S2 furgoncino, R4 Sinpar, R4 Rodeo, 65 Moke, R60 Tractor, R60 S, Toselli 78, Moto Guzzi Ercole, Disco 3, Mini ALL4 JCW, Moto Guzzi Cardellino, Fulvia GT, RE Himalayan, Ypsilon
Jaydub
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« Reply #10 on: 21 July, 2016, 07:48:18 PM »

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.
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John B
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« Reply #11 on: 21 July, 2016, 08:54:26 PM »

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?

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1961 Appia S3
1969 Fiat 850 Special
ben
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« Reply #12 on: 21 July, 2016, 10:23:27 PM »

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.
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John B
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« Reply #13 on: 22 July, 2016, 10:24:25 AM »


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.

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.
 

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1961 Appia S3
1969 Fiat 850 Special
lancialulu
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« Reply #14 on: 22 July, 2016, 11:58:35 AM »

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).
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