IMO, anything north of 160-ish is good. More important than actual numbers though is that all the cylinders are within about 10% of each other (some say 15%).

 

thanks. so i am sub 110 but all within 10% and no blue smoke.

would it be safe to assume i need a valve job?

 

Sub 110 ? Are you doing the test with the engine hot and with the throttle wide open ?

Steve

 

Sub 110 ? Are you doing the test with the engine hot and with the throttle wide open ?

JimPunkrockford's answer to GTA R's question (which was asked way back in post #4 ) would take us a long ways toward answering the original question.

Readings of 110 psi would be low for a warm engine with the throttles open. But if cold/closed, 110 doesn't sound so bad. So, which is it?

 

Static Compression

thanks. so i am sub 110 but all within 10% and no blue smoke.

would it be safe to assume i need a valve job?

Not at all. Static compression readings reflect several engine conditions but the chance of having all the valves leaking "evenly" is less than miniscule.

Since the motor isn`t smoking that says the oil control ring and 2nd ring are still wiping oil off the liners adequately.

With your discription my suggestion is to check your engine`s cam timing.
If the cam timing is off it will likely reduce the static CR.

One of the "urban myths" scattered by many sources was the added power from advancing the intake camshaft and retarding the exhaust cam a couple of degrees.
This might help but only at high RPM. In fact moving the cams in such a manner increases an already excessive amount of overlap killing low and mid-range torque/HP. The stock cams are not not going to reflect much power change at all due to their mild profiles.

Advancing cam timing needs to be clarified. Advancing the intake cam (clockwise) opens the valve earlier and retarding the exhaust (counter clockwise) closes the valve later. Both increasing overlap, reducing torque and reducing engine efficiency and reducing the static CR #s you get when checking the engine with a guage.

To be clear these 1750 engines came with camshafts timed at various points LC wise depending on whether Euro carbed models, or USA versions with variable intake timing. If it was a spica car it had the vvt unit and the timing was to be at 114 int (100 when advanced above 1700 RPM) and 102 exh.

Alfa issued a TSB changing weber carb`d versions to 104 / 104 in the `70s.
The Euro 1750 used a larger lift version of their standard lobe design, and LCs were set at 99.5/99.5.. The drivability of these cams improved as well when reset to 104/104.

If your car has Carbs now, set the cams to 104/104 LCs and recheck the CR. Should be a bit higher and drive much better.

If it still suffers the Spica curse, set the cam timing on the exh side to 104 and make sure the intake side is not less than 114. If it`s a bit outside the 114 mark (cam mark to the intake side of the cap mark) that won`t hurt either.

If there is leakage issues the only way to determine where the compression is going is with a leak down test.

 

...If it was a spica car it had the vvt unit and the timing was to be at 114 int (100 when advanced above 1700 RPM) and 102 exh...

Richard, you are confused. No 1750 SPICA motors came with VVT.
As far as I know VVT start with the 1982 l-jet 2.0 spider

 

would it be safe to assume i need a valve job?

It would be safe to assume nothing. Keep in mind a compression test doesn’t tell the whole story of an engines health and people often get hung up on the compression number. Typically if all compression values are within 10% then the engine passes the compression test. If you suspect you have a head problem I would do a leak down test.

 

Roger....
Back away from the keyboard slowly......

 

It may be that your gauge may is reading low. I've got 2 gauges and they read about 15psi apart. If your engine runs OK, you're not using oil and the relative readings are close then there's probably nothing that needs to be done.

 

If your engine runs OK, ..... nothing that needs to be done.

unfortunately the engine runs terrible. but i like your optimism

If you suspect you have a head problem I would do a leak down test.

i guess that would be the logical thing to do. then i can narrow this down. is there a thread about how to do a proper and comprehensive leak down test?

With your discription my suggestion is to check your engine`s cam timing.
If the cam timing is off it will likely reduce the static CR.

this has also been suggested in the past, i guess a leak down test first would be in order. but how would i go about checking cam timing? is there a thread or a book or something?

as always, all of this help is greatly appreciated

 

As far as I know VVT start with the 1982 l-jet 2.0 spider

It was introduced in 1980 on Spica 2L Spiders.

 

As always,
pictures of the offending motor would settle this.....

And as far as running poorly,you can spend the next year (some have !) going from suggestion to suggestion, changing parts and spending $$ or you can do what a competant mechanic would do.....
Trouble shoot each system in a logical order.
There are several books with this M.O. and it will save you time, money and grief.

 

is there a thread about how to do a proper and comprehensive leak down test?

I dont know, but there are some good YouTube videos on the subject. I would recommend that if you are not familiar with the leak down test to get a friend or find a mechanic who is. A miss diagnosis could be very costly.

 

Don't forget to dribble a little oil into each cylinder when doing the compression check. If you don't do this, you can end up with low readings.

 

Whoa, whoa - You're right, dribbling in a little oil will raise the readings if worn rings are the culprit. So yes, that's a diagnostic: if compression is low without oil, comes up with oil, blame the rings.

However, that doesn't mean:

1) you should always dribble in some oil before measuring compression.

2) if the readings are high with oil, then everything is fine.

 

My point is bad running can be many other things than low compression. Fuel, spark, etc.

 

Absolutely. Can be fouled plugs, bad rotor (burned) or cap (cracked or dirty inside). Those are the first things I look at.

 

I neglected to say anything about what it means if the readings do come up. I didn't say that the rings would be fine if they did come up as you imply I did in your second point. I think you misunderstood my comment, and just assumed that.

When I said, "If you don't do this, you can end up with low readings", I meant that it may be the case if the rings are worn, and it will result in those low readings.

It has been standard practice to use a little oil in the cylinder to see if that does happen. It is a check to see if the readings do come up, meaning that perhaps the compression rings are faulty; or if the values don't come up, valves are most likely dodgy.

 

As others have stated the running terrible is not caused by low compression in your case. 110 is not that low and they are even, so solve the other problems first. There are several tech articles about extreme wear in piston engines and the conclusion is that they can be run until the compression is so low they will no longer idle. I've seen engines run with numbers as low as 60 and once warmed up they run fine, of course they don't make the power they should.
If this was my engine I'd leave well enough alone and find the real culprit to poor running then only if I needed more power would I open the engine up.

 

dang

i am bummed about this. i bought a new compression test kit. and the compression seems okay now.

i really just wanted to know why the car runs so bad, bad rings would of at least given me something instead of just throwing money at this stupid car.

first pic is cold the second is hot.

so....
rebuilt the carbs,

new distributor and coil

good compression

should i still check the cam timing?

this thing is too much

 

Rebuilt carbs? I'm going guess the carbs are out of sync
New distributor, are you sure the timming is right?
It sounds like you have what you need, putting in new rings would be throwing money away.
Here is a good article on setting the carbs, Daves home page

 

carbs may indeed be out of sync. i need a sync tool and that link will be of great use, thanks

i believe the timing is right

Which carbs are you using - the full model number?

full number? i don't remember dcoe 40s xxxx....

Maybe your cams are flat......

interesting thought, i'll post some pics

It would probably be useful to define what the motor is doing:
Hard starting?
Rough idle? Rough running at certain speeds? At All speeds?
Lacking power at certain points?
Backfire out exhaust?
Backfire out of intake?
Is it worse cold, hot or all the time?
Blue smoke?, white smoke? Black smoke? No smoke?
Water in oil? Oil in radiator? Oil leaks around the head?

I'm sure there are plenty of other maladies, these are just off the top of my head.

If you can make a youtube video and post it, it may help in the diagnosis.

Sounds like you just need some tweaking and not a lot of money. I know this is not a SPICA motor but I find it interesting when you are dialing in the FI pump that as you go the motor runs crappier and crappier until the final twist of the screw driver and then every thing falls in place and it runs fine. Unnerving in the process though...

yes i should of said all this first, sorry

hard to start cold, rough idle, uneven idle, will go up then die down.

lacking power when you accelerate, also a large bog if you floor the gas pedal.

backfire out of intake, and i retarded the timing from the mark and it runs a little better.

no smoke, no leaks. here is a video of it running

thanks for the help everyone, and the shoulder to cry on :crying2:

 

Which carbs are you using - the full model number?

 

Maybe your cams are flat......

 

It would probably be useful to define what the motor is doing:
Hard starting?
Rough idle? Rough running at certain speeds? At All speeds?
Lacking power at certain points?
Backfire out exhaust?
Backfire out of intake?
Is it worse cold, hot or all the time?
Blue smoke?, white smoke? Black smoke? No smoke?
Water in oil? Oil in radiator? Oil leaks around the head?

I'm sure there are plenty of other maladies, these are just off the top of my head.

If you can make a youtube video and post it, it may help in the diagnosis.

Sounds like you just need some tweaking and not a lot of money. I know this is not a SPICA motor but I find it interesting when you are dialing in the FI pump that as you go the motor runs crappier and crappier until the final twist of the screw driver and then every thing falls in place and it runs fine. Unnerving in the process though...

 

I am joking about the cams, althou some here think all Alfa cams are worn.
This method of trouble-shooting is the least likely to get results as there are so many opinions to check.
On owner went on for a long while checking and replacing parts until he found that the exhaust pipe had been filled with acorns by an industrious squirel.
Do a proper trouble shooting method. System by system as a pro would do.

 

okay, checked the cam timing marks. i am assuming these are them and they are on at TDC.

i ordered a carb sync tool, so the carbs may still be out of tune here but here are some videos of the car running, the idle gets really fast after the car has warmed up, but like i said, we will see after i re-sync the carbs

 

Have you checked for air leaks in the rubber carbie mounts?
This will definitely make the car run like a dog when everything else appears ok.

Wazza.

 

i did a visual check before reinstalling the carbs. they seemed good, but i did not take them off the car to inspect. is there a way to test them? how do they come off?

 

You can check for air leaks by spraying starter fluid around the mounts. Some use propane gas. If the motor speeds up you likely have a leak.

 

ahh that's what i was looking for. thanks i will give that a try.

 

The theory of introducing some flammable gas into the intake manifold works. We recently did exactly that and appeared to find the culprit with the soft mounts. New soft mounts and $120.00 later the loping idle and lack of a decent reading with our vacuum gauge leads me to believe the starting fluid test did not perform as intended. Not sure where to go from here, has anyone had luck with the "smoke test" for vacuum leaks in the intake system?

Yes, we are off topic

 

The problem with starting fluid is that it mostly evaporates before reaching the suspected vacuum leak source. I use brake cleaner or carb cleaner. You can use water if you like. You'll know when it hits the leak......