John B
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« on: 16 July, 2016, 10:17:41 AM » |
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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 .......
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1961 Appia S3 1969 Fiat 850 Special
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simonandjuliet
Permanent resident
Posts: 2538
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« Reply #1 on: 16 July, 2016, 10:31:49 AM » |
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When I've got a few minutes I will pop a plug out and test mine
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AmilcarCGS, ApriliaCabrio,S2Aprilia,Ardea c'cino,S4 Ardea, Appia c'cino, Appia f'cino,B20 s4,4 R4 Sinpar, R4 Rodeo, 65 Moke, 2xR60 Tractor, 2xToselli 78, Moto Guzzi Ercole, Disco 3, Mini ALL4 JCW, Moto Guzzi Cardellino, Fulvia GT, RE Himalayan, Ypsilon
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lancianut666
Permanent resident
Posts: 1650
Slow but rough
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« Reply #2 on: 16 July, 2016, 02:22:48 PM » |
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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
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John B
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« Reply #3 on: 16 July, 2016, 04:14:06 PM » |
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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.......
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1961 Appia S3 1969 Fiat 850 Special
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lancianut666
Permanent resident
Posts: 1650
Slow but rough
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« Reply #4 on: 17 July, 2016, 08:58:50 AM » |
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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
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nistri
Megaposter
Posts: 530
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« Reply #5 on: 18 July, 2016, 12:51:48 PM » |
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90 psi is very good on the Appia and should be uniform on all 4 cylinders, Andrea
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Andrea Nistri
Ardea S2 Appia S2 Fulvia GTE Fulvia Sport 1.3 S Fulvia Montecarlo Fulvia Coupe 1.3 S
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John B
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« Reply #6 on: 18 July, 2016, 02:25:36 PM » |
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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
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simonandjuliet
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Posts: 2538
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« Reply #7 on: 19 July, 2016, 08:13:16 AM » |
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Checked mine yesterday - 105 psi
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AmilcarCGS, ApriliaCabrio,S2Aprilia,Ardea c'cino,S4 Ardea, Appia c'cino, Appia f'cino,B20 s4,4 R4 Sinpar, R4 Rodeo, 65 Moke, 2xR60 Tractor, 2xToselli 78, Moto Guzzi Ercole, Disco 3, Mini ALL4 JCW, Moto Guzzi Cardellino, Fulvia GT, RE Himalayan, Ypsilon
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John B
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« Reply #8 on: 19 July, 2016, 11:44:33 AM » |
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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
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simonandjuliet
Permanent resident
Posts: 2538
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« Reply #9 on: 21 July, 2016, 08:12:45 AM » |
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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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AmilcarCGS, ApriliaCabrio,S2Aprilia,Ardea c'cino,S4 Ardea, Appia c'cino, Appia f'cino,B20 s4,4 R4 Sinpar, R4 Rodeo, 65 Moke, 2xR60 Tractor, 2xToselli 78, Moto Guzzi Ercole, Disco 3, Mini ALL4 JCW, Moto Guzzi Cardellino, Fulvia GT, RE Himalayan, Ypsilon
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Jaydub
Megaposter
Posts: 344
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« Reply #10 on: 21 July, 2016, 07:48:18 PM » |
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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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1600 HF. S2.
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John B
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« Reply #11 on: 21 July, 2016, 08:54:26 PM » |
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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
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ben
Lapsed
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Posts: 456
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« Reply #12 on: 21 July, 2016, 10:23:27 PM » |
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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 » |
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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
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lancialulu
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« Reply #14 on: 22 July, 2016, 11:58:35 AM » |
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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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Its not the winning but taking part! or is it taking apart? Lancias: 1955 Aurelia B12 1967 Fulvia 1.3HFR 1972 Fulvia 1600HF 1972 Fulvia Sport 1600 1983 HPE VX 1988 Delta 1.6GTie 1998 Zeta 21. 12v
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