i brought my 91 RS (305ci) to a mechanic. he has done a valve adjustment so far. but today he said that he found i have a loss of compression in two of my cylinders on the passenger side, so the car is only firing on 6 of 8 cylinders. what causes this ? i dont want to be uninformed, but i dont want this mechanic to "take me for a ride"(pardon the pun). any help on this would be greatly appreciated.

 

If they are 2 adjacent cylinders, then it's often a sign of a blown head gasket.

Why is the car at the mechanic getting compression-tested in the first place? That's kind of like root canals or something; while it may be useful and necessary and occasionally even desirable, people don't ordinarily just decide on a lark to casually have it done. Something wrong with how it runs?

 

Don't get scamed on a new rebuild.
Buy a tester and check it yourself.
Search here or anywhere on the net for a how-to...........

 

Just because you have a compression loss doesn't automatically mean you've got two dead cylinders. If the leakdown test and compression tests exceed "specs" then you're supposed to do something about it.


Think of all the things that retain compression; valves, head gasket, and piston rings. These three things are the most common (in no order) and many more things could affect compression and leakage... But focus on those. Basically, the most effective method to determine what exactly is wrong with your car is to DOUBLE CHECK the problem and then remove the head. There's a trick about putting a piece of paper up to the tailpipe when the car is on and if it sucks it back in then you've got a burnt valve- but I've never actually heard of anyone confirming a burnt valve using this method.


If you love your mechanic as much as your car, go ahead and let him work on it. If you're short on money and not afraid to get your hands dirty- yank that head after confirming his findings.


You're not burning any oil or coolant, are you?

 

im not burning oil or coolant. my engine troubles started out with a loud ticking noise in the engine. i tried to work on it myself, but i couldnt fix it, so i decided to bite the bullet and talk to the professionals. i dont know why they tested the compression in the first place, but all i know is i want my baby back on the road, while gaining a little wisdom along the way. thank you for the quick responses.
im not sure if the cylinders are adjacent or not.
i really hope its not the piston rings!
the previous owner rebuilt the engine recently before i bought it. maybe thats part of the problem? maybe he didnt do a good enough job. compression is just Greek to me.

 

long story short: you hear something wrong, the mechanic knows what it is but wants to feed you lines about what you "should" be looking at. you spend a grand fixing it, he gets paid. win-win situation right? or wrong? take a step back and see what's really going on.


get a compression tester, they're like $10 at Harbor Freight or you can even rent one at a parts store. they come with instructions that couldn't be easier.

 

Hows the oil pressure?
You need 10 lbs. for every 1000 rpm's in a sbc.
And check the exhaust manifold's bolts, if they are loose a "ticking" noise will be present.

 

Loud "ticking" noise often is created by compression exchanging between 2 cylinders.

Definitely get a 2nd opinion, or test yourself, or whatever, before just tearing into it or allowing someone else to do the same.

 

Can't stress it enough to get a second opinion at the minimum!! Especially when a thousand dollars of work is on the line lol

 

the guy from the shop calls me today and said it was he was going to replace the valves in my passenger side head, and send it to the machine shop, for a low low price of $1800. i said "there's no way im going to spend that on a 305"

he said alright, come pick it up. so i did and it runs just as crappy as it did when i brought to them (i paid them about $700 for work so far). that dude was totally trying to rip me off i know it. i could buy new heads for half of that. the car also shut off on me 4 or 5 times driving it home from the shop. the oil pressure was pretty low and i noticed a significant decrease in power than normal also.

 

$1800 to swap some valves!??!!?!

you can go buy a pair of complete AFR heads and still have beer money left over for that price!

 

 

Not really that much of a savings though, he still needs them installed.

 

it cant be that hard to bolt on some heads right?

 

Mostly it just takes some time.

 

oh okay. i think thats what im going to do. just get some new heads. or i might dog that 305 till it blows and get a 350. who knows.

 

The problem with that is that you never know where you and the car will be when it finally blows.

 

True but the tow home would probably still cost less than any temporary repairs!


Just make sure you always got your cell phone with ya!

 

what all did they do, and what's the labor rate you're being billed at?

 

valve adjustment and a bunch of bs = way too much..........

Bro, try and find someone who can help you at no charge (guys like us) in your area.
That's your best bet, otherwise you will get reamed with no lube......

 

to change valves and machine the head which I assume to mean just shaving a small amount to make sure it is flat is very easy fairly cheap work. at least cheap compared to 500bucks worth.
and what the hell 700 bucks and not a fix yet? what is he doing? charging you labor, beer money, money for meth, plus a few nights for him in a hotel plus some more money to rent a hooker for a few nights?

I would ask for reciepts to see what the heck he is spending all that hard earned money on.