If you haven’t encountered
this term before, in this context it refers to measuring the maximum
pressure in the cylinder while the engine is cranking over on the
starter (with the ignition disabled so the car doesn’t start).rubber auto oil seals Lexus.
Check the compressions if:
it is a new (to you) car – if this wasn’t already done prior to purchase
the car has been unused for some time (months, not weeks) as this can cause rusting on the valve seats and consequent lack of sealing
it is some time since you have done one and there is an unusual or elusive problem.rubber auto oil seals Lexus.
Compression testers are relatively cheap (cheaper to buy a gauge than to drive in and pay someone to do the job). Their instructions, or workshop manuals, outline how to use and interpret them. The only comments I will add are:
if you can’t find the correct cranking compression pressures listed for your car, work on 20 times the compression ratio as the figure for a good healthy engine. (For example, 8.8:1 should give about 20 x 8.8 = 176 psi on the compression gauge).
in the absence of any data from the manual, the best indication of condition is that the compressions between different cylinders don’t vary by more than 10 psi.rubber auto oil seals Lexus.
the actual compression readings will vary from those in the manual if the engine is modified.
A simple approximate compression check is to crank the engine over with the plugs in but ignition disconnected, and listen to the beat of the engine. It should be even. To hear what very “uneven” sounds like, remove a spark plug and crank it again (listen to the beat, not the whoosh of air in and out of the plughole).rubber auto oil seals Lexus.
Air leaks
As noted above, air leaks in the inlet tract can be the source of an elusive problem. Some sources are:
The gasket between manifold and head. In particular, the A series manifold gasket is very thin above and below the inlet ports and fails at this point relatively easily.rubber auto oil seals Lexus.
Cracks in the heat shield which extend into the join between carb and manifold
Faulty brake booster (if fitted). To eliminate this as a source, disconnect the vacuum hose from the manifold to the booster and plug it off.
Faulty PCV valve on mid-late 60’s B’s and Midgets. This can be accompanied by excessive oil consumption.
Carburettors or manifold loose. Unusual, but yes, it can happen!rubber auto oil seals Lexus.
Check the compressions if:
it is a new (to you) car – if this wasn’t already done prior to purchase
the car has been unused for some time (months, not weeks) as this can cause rusting on the valve seats and consequent lack of sealing
it is some time since you have done one and there is an unusual or elusive problem.rubber auto oil seals Lexus.
Compression testers are relatively cheap (cheaper to buy a gauge than to drive in and pay someone to do the job). Their instructions, or workshop manuals, outline how to use and interpret them. The only comments I will add are:
if you can’t find the correct cranking compression pressures listed for your car, work on 20 times the compression ratio as the figure for a good healthy engine. (For example, 8.8:1 should give about 20 x 8.8 = 176 psi on the compression gauge).
in the absence of any data from the manual, the best indication of condition is that the compressions between different cylinders don’t vary by more than 10 psi.rubber auto oil seals Lexus.
the actual compression readings will vary from those in the manual if the engine is modified.
A simple approximate compression check is to crank the engine over with the plugs in but ignition disconnected, and listen to the beat of the engine. It should be even. To hear what very “uneven” sounds like, remove a spark plug and crank it again (listen to the beat, not the whoosh of air in and out of the plughole).rubber auto oil seals Lexus.
Air leaks
As noted above, air leaks in the inlet tract can be the source of an elusive problem. Some sources are:
The gasket between manifold and head. In particular, the A series manifold gasket is very thin above and below the inlet ports and fails at this point relatively easily.rubber auto oil seals Lexus.
Cracks in the heat shield which extend into the join between carb and manifold
Faulty brake booster (if fitted). To eliminate this as a source, disconnect the vacuum hose from the manifold to the booster and plug it off.
Faulty PCV valve on mid-late 60’s B’s and Midgets. This can be accompanied by excessive oil consumption.
Carburettors or manifold loose. Unusual, but yes, it can happen!rubber auto oil seals Lexus.
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