out of ideas 76 124 spider 1800

[majicwrench]

Just to save you the time....

Setting at TDC and filling w compressed air will force piston down every time. You have to secure crankshaft somehow.

Keith

[RAD]

tonight I took a closer look and examine the cams and found nothing wrong there checked under the distributor cap and no problem there. so far all the ignition system component has been replaced everything from the coil distributor cap rotor points condenser plug wires spark plug,have been replaced, also timing belt and valve clearance has been corrected. someone mentioned something about funny oil well you know the first thing I did was change the oil and filter and it did smell funny and very thin possibly they added something to loosen a lifter or something for whatever reason it smelled like it had bad gas in with the oil. so it would makes sense to have a bad or stuck lifter. how can I check the lifters?

[hayesbd]

I once had a distributor cap on a 600 that had an internal crack/void, causing a similar issue. There was no tracking to see on the inside of the cap - I had to break it apart later to discover this problem. It's a long shot, but if you happen to have a spare cap, you might just swap it out.

Brian

[So Cal Mark]

Again, magicwench i wrong; a leakdown test will not spin the motor if the piston is at tdc. The pressure is pushing down, but the piston/rod is straight up so it doesn't turn the crank. The motor only turns if you're not exactly at tdc. Leakdown tests are much more informative than a compression test.

[toplessexpat]

I once had a distributor cap on a 600 that had an internal crack/void, causing a similar issue.

I had a similar issue on my '76 a while back. Tiny crack meant that #2 was acting up, similar issues to what you described. I replaced the cap and it got MUCH better (but not perfect), I replaced the entire ignition with one of Mark's distributor-less ignitions - and it's now perfect (famous last words, I'll go down to the garage now and she wont fire knowing my luck!). I found some poor innards in the old dizzy which I replaced too so I have a spare.

[RoyBatty]

That is correct Mark.
That is why it's the only way we check compression on aircraft recip engines.
Granted, it can be tricky to get things squarely on tdc, but I manage to do it in my driveway on a regular basis as required.
The thing that works best for me is to position the cylinder as close to tdc as possible, then apply only about 30psi to the cylinder and then using a socket on the crank pulley nut with a large drift, I rock the cylinder back and forth slightly. The low pressure applied will let you feel when you are truly on tdc. It goes without saying that you need to be careful doing this to avoid pinching your fingers and such.
Once tdc is found I remove the drift from the socket and bring the pressure up to 80psi to perform the check.
Once you learn to interpret the results and how to use the tool, you can find out whether you're leaking past the rings or the valves or whether or not you have a head gasket leak between cylinders or into the cooling system.

[majicwrench]

Again?? Was I right or wrong about the camshaft lobes??

Again, Mark is wrong, sorta. Try it and see. You have to have it EXACTLY at TDC is cannot be off 1/2 degree or piston will be pushed down. Try it and see how it work for you. Good luck. For someone who doesn't do this on a regular basis, good luck.

[MrJD]

call me crazy... but could you not get it close to TDC, put it in gear, and set the ebrake?

There, done. Fixed.

[majicwrench]

Sure, like i said, gotta secure crank somehow, or fight it getting to TDC exactly. Still, engine may turn enough to start opening valves, lots of slack tween crank and tires.

Bottom line, leakdown test is not gonna show the OP much. If compression is fine as he says it is, really spinning wheels.

[Kevin1]

I am no pro, but from reading above it seems there is good compression in all 4 cylinders with correct valve clearances, valve timing, and ignition timing. Wouldn't it stand to reason that the first problems to eliminate should be either no spark or no fuel?

Does the car hace a mechanical fuel pump? If it is leaking it could be diluting the oil with gasoline.

Every once in a while you get to a stumbling point where getting it to a local mechanic might be a good idea. One worth their salt would probably diagnose it pretty quickly.

[chrisfiat]

I am no pro, but from reading above it seems there is good compression in all 4 cylinders with correct valve clearances, valve timing, and ignition timing. Wouldn't it stand to reason that the first problems to eliminate should be either no spark or no fuel?

Does the car hace a mechanical fuel pump? If it is leaking it could be diluting the oil with gasoline.

Every once in a while you get to a stumbling point where getting it to a local mechanic might be a good idea. One worth their salt would probably diagnose it pretty quickly.

bingo

[RAD]

all of the common sense stuff has been eliminated it has spark it has fuel it has an electric fuel pump. I did the leak down test my question is should it hold the air pressure I pumped in (100 lbs) for short time? it stayed for 2-3 seconds or so. placing the cylinder on top dead center slowly increase pressure it stayed on TDC and no noticeable leaks in a radiator hose or the carburetor very very slight hint in the exhaust I mean taking a hose put it inside exhaust tailpipe and listening, good? Bad? so tomorrow I'll check the tappets

[So Cal Mark]

if you're hearing air in the exhaust then an exhaust valve is leaking. A leakdown tester will show the percentage of leakage, more than 10-15% is too much

[RAD]

so you're telling me it should hold a 100 lbs that I put in for more than 2-3 seconds. all the cylinders tested the same. leak down tester is something I just made out of a blowgun, pressure gauge, and a broken compression gauge

[RoyBatty]

this leakdown test is also known as a differential pressure test.
you are applying a known amount of pressure to the cylinder while at TDC and comparing the amount of pressure held in the cylinder to the amount of pressure that was applied. this value, coupled with where you hear the air leaking from its the a great way to diagnose a problem such as yours.