Gamble?

[gregmercer]

Heres the scoop....<br /><br />I have a 1993 Volvo 230. It overheated one day due to insufficent water from the garden hose, the temperature got around 250 degrees. It has 150 psi of compression on cylinders 2,3, and 4. It had 50 psi on cylinder 1 with 90% leakdown. I pulled the head hoping to find a blown head gasket. The head gasket looked fine so I pulled off the cam, lifters and valves. The valves look fine to me.<br /><br />Now I don't know what to do, I could take the head to a machinest, spend lots of money and have them plane it and do a valve job, put a new head gasket on it and hope it fixes the problem. It would unless... I have bad piston rings in that cylinder. Then I would have spent all the money for nothing.<br /><br />What would you guys do? What are the chances I have bad piston rings in just one cylinder? I kind of think the rings are good because it wasn't smoking and burning oil.<br /><br /><br /> Are there any problems I could be overlooking that are causing the low compression in that one cylinder?

 

[calwldlif]

Re: Gamble?

Magnaflux the head.<br />Can you remove the valves and <br />reassemble? Valve could be warped.<br /><br />I would think the head is cracked.<br />But thinking gets me in trouble

 

[gregmercer]

Re: Gamble?

I can't visually see any cracks but I guess its possible.<br /><br />I'm pretty sure magnaflux only works on cast iron heads though, mines aluminum. I have allready removed the valves and I can put them back.<br /><br />Thanks!<br /><br />Greg

 

[cjflanagan]

Re: Gamble?

 

[cjflanagan]

Re: Gamble?

Sometimes valves (exhaust in particular)will 'cup' when they overheat (typically when running real lean and not just over heat), but my point is, how are you so sure that they are alright?

 

[calwldlif]

Re: Gamble?

aluminum? Kool<br />I don't know what to tell you.<br />250 deg closed system just doesn't<br />seem that high. I was thinking<br />cast iron head and they do crack for<br />various reasons. How much room in your<br />motor area? can you pull the pan?<br />if so you could change the rings.<br />I guess I would have the head checked for warp<br />/valve seat integrity/ pressure holding.<br />it is easier/cheaper. if it checks then<br />deck flatness/crack.<br />You sure the head gasket is OK?<br />They do let go. Not always easy to see.<br />It would explain the prob. #1 cyl is on the end!<br />Not thinking to clear about now.<br />hope its the gasket.<br /><br />Check the deck and head for flatness first,<br />look real close at the gasket on the end where<br />#1 cyl is(outside edge) then do what I scribled above.<br />I hope you find it.

 

[Kevin70]

Re: Gamble?

You can put a spoonful of oil in the spark plug hole, turn the engine over a few times to distribute the oil, then test the compresion again. If there was an increase in pressure, then it's a ring problem.

 

[gregmercer]

Re: Gamble?

I don't know that the valves are perfect. All I know if from looking at them with my un-trained eye they look to be good. <br /><br />I also am not sure that the head gasket is ok, I'm pretty sure that coolant would have leaked into the cylinder is the head gasket had a leak though....<br /><br /><br />I plan on getting the head checked for warp. Thanks a lot for everyone's help!<br /><br />I put some oil in cylinder number one and didn't notice any compression change.

 

[Don S]

Re: Gamble?

For anyone else reading this thread, this is why you do your troubleshooting BEFORE you take it all apart. <br />Greg mentioned he had a 90% leakdown, at that point, listening would have told the story.<br />If you could hear the air coming out the carb, that indicates the intake valve is source of the leak, coming out the exhaust would indicate a problem with the exhaust valve. If you could hear the air in the valve cover, that would be rings or piston, cylinder or leak to an oil passage. Coming out the sparkplug hole next to the offending cylinder would indicate a blown head gasket between the two cylinders.<br />Bubbles in the cooling system would be a leak into a cooling passage from a possibly bad head gasket.<br />While it wouldn't tell you exactly what the problem was, it would sure narrow down the search. As an example, if you hear most of the air coming out of the carb, it could be a valve is warped, or stuck, or even the seat is damaged in the head itself. But at least you know it's not a hole in a piston or a cracked cylinder wall, or blown head gasket, or a damaged exhaust valve.

 

[gregmercer]

Re: Gamble?

I did a lot of listening before I pulled the head but couldn't isolate where the air was escaping. There were no bubbles in the coolant, I couldn't feel any air comming out of the dip stick hole or valve cover, and couldn't feel the air comming out of the air filter. I could hear the air escaping but couldn't isolate where it was escaping from.<br /><br />Don S - How likely do you think it is that my piston rings are shot?<br /><br />I don't know whether to gamble and get the head work done and hope it solves my problems or not.<br /><br />Greg

 

[gregmercer]

Re: Gamble?

One more thing - there was no excessive play in that piston and no markings on the cylinder wall. Is there any other ways to check for bad rings without pulling the motor out of the boat and tearing it apart?<br /><br />Greg

 

[Gary H NC]

Re: Gamble?

At this point i would get the head checked and put it back together.A bad head gasket is not always visible..<br />If it was piston rings i would think the cylinder walls would show that.<br />Just my 2 cents worth..<br />Good Luck!

 

[gregmercer]

Re: Gamble?

I am thinking about getting it ported and polished while the head is at the machinest. Think I could gain a noticable amount of power???<br />Anybody done this on there volvo 4 banger before?<br /><br />Greg

 

[calwldlif]

Re: Gamble?

With out seeing you head its hard to<br />know. <br />Porting will depend on the "land" area between<br />valve seats. If larger valves are even available.<br />Polishing could backfire on you because,<br />too smooth won't atomize you fuel well.<br />Exhaust polishing is limited by the manifold.<br />I would have the chambers "CC"ed for balance<br />and if you don't have any roller valvetrain<br />parts I would look into availability.<br />Alum head are machined and port surface <br />is well addressed. Be carefull when surfacing<br />because increased comp/ratio will demand higher<br />octane. Check on avail of different thickness<br />head gasket to offset head surfacing if it turns<br />out its warped.<br />I would build for smooth balance and rpm turning<br />ability.<br />You might look into a "performance" head already<br />built with bigger valves/ wedged chamber.<br />Remember the top is dependent on a good bottom.<br />I hope you find the compression leak and its <br />an easy fix.