Getting a car for basically nothing, hoping to fix

hal

Messages
393
Location
NC
I have come across the opportunity to obtain a '91 Mazda 626. The car runs and drives, but the current owner says it has low compression in 2 cylinders. He also said his mechanic claimed it has something to do with the valves in these two cylinders. I'm guessing this is either caused by a burnt valve or possibly just bad carbon deposits not letting the combustion chamber seal. I guess my question is this- if the problem is maintenance-related and not a detrimental mechanical problem, what would be the best and most effective way to go about making this engine run better? I.E. making the valves seat better and restoring lost compression. Any info would be greatly appreciated as I am planning to fix this car up and give it to someone I know who is in need of one. Thank you!
 
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Messages
25,046
Location
ON, Canada eh?
Do you know if the valve-lash is just out of adjustment? I would take the rocker cover off and check the lash. I could see 1 burnt valve but 2 of them in an engine is pretty rare IMO.
 
Messages
2,759
Location
CarMax
What can a valve job cost? $500 or so? Assume the rest of the car is in good condition, is it worth $500+ to spend on this particular car? The simple ideas like Seafoam and a valve lash adjustment are good ones, and plenty cheap to do. Beyond that you have to decide if its worth the $$ to fix this car or to move on to something less needy.
 
Messages
8,988
Location
Marshfield , MA
I'm guessing the engine has mechanical lifters. Adjusting the valves may help, My BIL got the compression up on an Isuzu Trooper 4 banger, simply by setting the valves. I didnt get so lucky with a CRV. I had to replace 2 exhaust valves. I just bought 2 valves, lapped them in and replaced the Head. Valves and gaskets cost about 200$
 
Messages
25,046
Location
ON, Canada eh?
Even if you have to have the Engine rebuilt or put a used engine in it, it's still cheaper than new car payments, even if you only get a year out of it! ;\)
 
Messages
36,003
Location
ME
You can get an ebay head shipped for around $100 with valves etc included if you don't want to mess with a machine shop. Losing compression on two cylinders can easily be a head gasket which you'll find as you tear it down. Worst case is you'll have $50 worth of scrap metal, and learned something you would have had to pay a technical school to teach you! Several years ago I made a new years resolution to get "inside" an engine and learn something... so I got a 1994 Dodge spirit with blown head gasket for $160 and did in fact learn something and fix it perfectly, with only instructions off the internet and no previous experience!!!
 

hal

Thread starter
Messages
393
Location
NC
wow thanks for all these replies people! i did not even think about valve lash adjustments, it really could be that simple. the engine (as far as I know) has no irregular noises so I don't think anything is bent. if the valves are hydraulically-adjusted then there could be an oil flow issue, probably fixable though as well. I'm going to do all the maintenance that I can once I determine the actual problem. and seafoam is not a bad idea either. the engine has 164k miles on it, transmission has under 50k. the body/interior is in pretty good shape except for needing some paint. i haven't tried replacing valves in a head before but if a replacement head is ~$100 then that might be the way to go since i have done a headgasket before. i really know nothing about Mazda engines though- have never owned one, but this is a 2.2L I4 (I think). Looking at the car tomorrow afternoon, and probably picking it up. This is going to be a learning experience.
 
Messages
36,003
Location
ME
There are tests for screwed valves. One includes putting a dollar bill over the tailpipe, if it gets sucked in it means a bad exhaust valve. When looking at the car, pay a stupid complement "oh the interior's nice and clean" then look underneath and sigh heavily (and nonspecifically). Whip out your offer in small bills, cash, and say it's what "I can give you".
 
Messages
464
Location
Ft Lauderdale Fl
If the headgasket's bad you'll (generally) have water in the oil. Easy to spot on the dipstick. Given the age, it could have wrung a timing belt and ticked a valve. My 2c Jorge
 
Messages
25,212
Location
Upstate NY
I would run a compression test to verify compression then dump into any bad cylinders a little oil and retest. If the compression goes up to equal the other cylinders, then the rings are the cause otherwise its valves. If its valves I would try adjusting and see if that helps. If not I would look at a head off ebay for $100 assuming it was a head that had a valve job.
 
Messages
5,570
Location
New Zealand
Is this the 12 valve engine? If so,they have hydraulic lash adjusters....and no problems with the valves.But lots of cyl head problems - they warp badly,they crack,and go soft.New heads are cheap,but as they are made anywhere but in Japan,the quality is very poor.
 

hal

Thread starter
Messages
393
Location
NC
yea its the 12-valve 2.2L sohc I4. im hoping its just a valve lash problem. i have found a good guide on how to correct problems with that aspect. you basically gotta clean out the oil passages under the lifters or whatever by hand b/c they can get sludgy over time and fail to keep the valves adjusted. sometimes an engine flush works so i may try that first. if the head is warped i would think there would be coolant in the oil or vice versa.
 
Messages
5,570
Location
New Zealand
Never had any problems with them holding a valve open,mostly they collapse and become noisy.They are cheap and easy to replace,but when you times by 12 it gets expensive,but it's usually only 2 or 3,you just need to find which ones. These are a good engine,and the only problem I've had is with the cyl head - they can fail so many ways,they end up with various symptoms.As well as working on hundreds (I'm a mechanic,and had my own business for 11 years) I owned one that did over 400,000km....but we put 3 heads on it.In the New Zealand and Pacific Rim market they are also called a Capella and Ford Telstar.
 

hal

Thread starter
Messages
393
Location
NC
well, the car is mine now :) and in 10 minutes i fixed the misfiring completely. bad spark plug wires. there was a LOT of carbon in the engine from the misfiring, once i fixed the wires it smoked a bit when i revved it but since then it hasn't smoked at all. i have not run a compression test yet but with the ignition problem fixed the engine feels very smooth, idles fine and has good power, so the compression can't be too bad. it needs some things- fuel filter, oil/filter change, new plugs and wires (im using some old wires off a civic for diagnostic purposes), slight exhaust leak around the manifold so probably a new gasket there, definitely an intake cleaning and fuel system cleaning, change the ATF, valve cover gasket, check the hydraulic lash adjusters to make sure they aren't gunked up, and probably a few other minor things. might could use an auto-rx treatment or something but i am still weary about engine flushes. aesthetically the car is really good for its age, interior is real clean- it just needs some exterior paint. it leaks a little oil but not bad enough to be a problem, and there might be a slight power steering pump leak but honestly im not concerned about that. it probably burns a little oil but i did not see any abnormal smoke when i revved it (after fixing ignition problem), and i don't see any behind me when driving it down the road. there is no rust anywhere under the car, it has one tiny spot on the hood and thats it. the exhaust is loud b/c the muffler is old but i kinda like it that way. so yeah, i am pretty sure this is gonna be a good car- she just needs some maintenance. i can tell the previous owner took care of it as good as he could, plus it has service records. and everything on it works including the a/c, power windows/locks, etc. i'm pretty stoked about this, definitely got a good deal :)
 
Messages
36,003
Location
ME
Haha that's awesome. Probably a drinking buddy said, "you know it's the valves..." After the most basic maintenance, go rod the snot out of it. That smoke was unburnt gas and you'll find a lot of that in the oil so make changing that priority A # 1.
 
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