Why is compression so low?

I've posted about this car before, engine rebuilt and still won't
start...

Old post -
http://groups.google.com/group/alt.autos.honda/browse_thread/thread/795504a695d910a2?hl=en

The thing is... I said all cylinders have compression, but I never
asked my buddy what the compression was. So, today I checked for
myself, and saw that the cylinders only had 90ish compression, and I'm
reasonably sure that's the reason the car won't start. The rings and
valves were all replaced, everything was torqued back to factory specs
with new gaskets blah blah... any ideas on why the compression is so
low?

 

Didn't read the old post, but if everything is new and good, then the
timing of the valves may not be 'in phase' with the crank. As if the
timing chain or belt skipped a tooth or three.

 

I'm with Brent - recheck the valve timing (the timing marks on the cam
pulleys compared with TDC). I bet you will find it at least one tooth off.
90ish compression won't prevent an engine from starting but valve
mistiming - which usually shows up as gross ignition mistiming - sure will.
Be sure to pull the engine through by the crank turning only CCW or the belt
will jump more.

In the original thread I saw you set the ignition timing by eyeball on the
distributor, but you will need a timing light to get it close enough to run
right... maybe even to run at all. First check the valve timing by the
marks. When the valve timing is right the distributor should go right back
where it was originally and it should be good.

Mike

 

Cam timing way off? If the valves open and close at the wrong times, it
won't build proper compression.

 

That can happen when the timing belt or chain is installed. If the
timing isn't right the valves don't close at the right times to get full
compression.

If the rings are no good or won't seat, that can blow the compression
out too. You can try a spoonful of oil into the plug hole just before
testing the compression again. If the compression comes up, you have
faulty rings, if not, look to the valve timing.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos: Non members can still view!
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If you failed to prop the throttle open, and the engine was dry, the
compression will be WAY LOW. You may have damaged the igniter too when
you cranked with the wires disconnected. Have you listened to the fuel
pump, and tried a bit of starting fluid to see if it will fire up even
for a second?

'Curly'

 

Soooo, find out WHY its so low!

Start with a leak-down test. If there are components leaking that
shouldnt you can find them easily with some smart listening.

Leakdown testers are available for under $100 and I just saw one very
cheap at Harbor Freight in their recent sale flyer. If you do ANY engine
work this tool will save you LOTS of guesswork.

-SP