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Author Topic: compression down  (Read 1756 times)
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« on: 21 August, 2009, 12:36:26 PM »

Hi, Just came back from garage, news not so good. compression down no1= 50 no2=60 no 3=150 no4 =160.
What next,is this a major job? Cry Cry Cry
Rebel Poster
Posts: 980

« Reply #1 on: 21 August, 2009, 01:51:06 PM »

Oh dear, but it depends on what the diagnosis is. It is likely either worn or scored bores, sticking rings or a valve that is not seating fully. If it is sticking rings just driving the car can improve it, anything other means diving into the engine. A rebore with the associated parts will cost 500+. Having the valves reground should cost less than 100. If you rotate the engine so that the valves are fully closed and pressurise the cylinder with compressed air you should be able (if the leak is bad enough) to tell if it is the valves (leaking through the ports) or the piston (leaking out of the dipstick tube).

1969 Fanalone, Mazda RX-8, Fiat Multipla
« Reply #2 on: 22 August, 2009, 07:59:06 AM »

With those sort of pressures I am surprised the car was running! another way of checking is to pour some oil into the bore and redo the compression check if the compression increases then the leakage is past the piston rings, as Neil says this may be because a ring is 'stuck' and not fully expanded or the splits in all the rings were in line when/if the engine was rebuilt or because the bores are worn from mileage or scored, was the car using a lot of oil prior to the garage report?. If the oil makes no difference then it would indicate a lack of seal from the valves. Either way it looks highly likely the engine needs a rebuild. If it is the valves I have a complete head you could have to rebuild and then just swap over it would make the job quicker as you can just swap heads rather then remove yours, rebuild and then refit. I can also supply this head to you fully rebuilt; valve reground and cut etc.
Senior Member
Posts: 175

« Reply #3 on: 23 August, 2009, 05:09:14 PM »

Hello Bill

With these sort of compression figures, it all points to a gasket failure between number one and number two bores, and compression is escaping between them.

Roddy Young

Roddy Young
Dunfermline, Fife

1970 Fulvia Sport S1 1.3S
1972 Fulvia Sport 1600
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