compression check results

[tilleytr7]

ok, here are the results that i got when i did a pressure on my 1980 tr7, cylinder one 105, cylinder two 120, cylinder three 120, cylinder four 105. are these numbers that would show that i might have a broken ring, or that the hose off of the valve cover might not be ventilated enough, thanks chuck.

[jclay (RIP 2018)]

It could be a broken ring or a leaky valve. You should do a cylinder leak down test.

Since you did the compression check and two of the cylinders tests low, then a cylinder leak down test will help you determine the cause of the weak cylinder. Special equipment (leak down gauge) is required which can be purchased at most auto parts stores. With all the spark plugs removed, rotate the engine so that the cylinder to be tested is on top dead center and ready to fire. This will assure that the valves are closed. Install the leak down gauge in the spark plug hole and apply air pressure.

The gauge will register the pressure drop indicating the percentage of leak. In addition, by listening at the exhaust pipe or air intake system or the oil breather you may hear escaping air, which means one of the components, is leaking. Example: air out of the exhaust pipe means the exhaust valve is leaking. Air coming out of the intake, an intake valve is leaking. Air coming out of the breather tube or oil dip stick tube is ring blow-by. By removing the radiator cap and observing the coolant, you can tell if there is a blown head gasket and or a cracked head if there are bubbles.

If the air is coming out of the exhaust/intake, check the valve clearance first.

Hope that helps!

Have fun, drive fast & safe, be kewl,

jclay

[Hasbeen]

Chuck, those compression figures do not mean all that much. The
pressure depends on so many things, that the only indication is from
the difference between cylinders. What cranking speed, how warm is
the engine, was it run recently, what cam is in it, how long [ie
months, or years] since it was in regular use, etc?
As Jclay says, a leak down test may give you a bit better handle on
the state of the thing.

YOURS ARE NOT TOO BAD.

Do you have a problem you are looking to locate with these tests, or
are they just general maintenance?

If the car has been in regular use, I would give it a bottle of STP,
oil treatment, & see if that helps. If its been out of use for some
time, see below.

When I bought my present 7, it had been retired from rallying, with
a clutch which would not disengage, 3 years before, & would not
start. It is a UK spec engine, & I gave it a compression test,
before I bought it. It had, 1 to 4, 140, 140, 115, 115, PSI, on a
slowish cranking rate.

When I got it home, I got it going with some fuel & electrical work.

The oil was very dirty, so I gave it a change with 10W30 cheep super
market oil, & gave it 2, 15 minute runs, around my bottom padock. I
figured this would get any surface rust off the bores.

I then gave it an oil filter, & a change to a highly detergent diesel
oil, 20w50, {I use Shel Rimula X] & a bottle of STP oil treatment.
This to free up any gummed up rings, & clean a bit deeper than the
first oil change.

The thing was now road registered, so I did about 300 miles on that
lot. By then the oil was pretty dark, & I gave it another filter, &
a quality 20W50 [older engine] oil, with another bottle of STP.

When I did another compression test, 500 miles later, it had 1 to 4
180, 180 175, 180 PSI. It has since done about 40,000 Km, [25,000
miles] & is going strong. I always run STP in anything which may sit
for any tine, unused, as it prevents the oil draining, & surface
rust forming. It also prevents things getting gummed up, as the oil
dries out.

Most engines will benefit from a good clean out, but, just be aware,
that some are only held together by the gunk in there, holding
hands. Cleaning out one of these will only hasten the inevitable
rebuild. If only we knew some way of telling the difference, before
we start.

Hasbeen