where to next?

[simplydave]

1985 90 hp cross flow. Have 117 lbs compression on three cylinders and 85 on the bottom port cylinder. If I pull the head what should I be on the look out for? Does the entire power head have to come off to correct the low compression?

 

[Faztbullet]

If I pull the head what should I be on the look out for?

Broken/rolled ring .

Does the entire power head have to come off to correct the low compression?

Yep...

 

[boobie]

If it's just a blown head gasket it doesn't. Pull the head first.

 

[emdsapmgr]

Agree, pull the head and examine the stainless compression/seal ring on that head gasket. If it's broken or deteriorated-on the low compression cylinder, that's probably the problem. If that compression/seal ring is intact, then shine a light on the top piston ring and see if it is still in one pc all around the piston. If the ring is gone, likely you will see severe pitting on the head face and the crown of that piston. These older crossflows go thru piston rings a lot-common problem.

 

[tommarvin]

Why is it when there's a bad cylinder it's seems to always be the bottom/lowest cylinder? Why is that?

 

[emdsapmgr]

Depends on the failure mode. If it's due to an internal water leak in the exhaust chest, resulting in a bad cyl-it's most common on the bottom cyls.

 

[simplydave]

ok, pulled the head and the gasket looks ok as far as I can tell. The combustion chamber on the lower piston was clean, like water was in it. The upper had carbon on it. I am at a loss as to how to find an inspection port to see the ring on the piston. Any help there is appreciated. The head bolts seemed to have neversieze on them, I thought they were supposed to be torqued dry, Oh, the cylinder itself didn't have any deep scratches or pits, just the look of a cylinder after 35 years of use. Can that be honed or the glaze cleaned up without a complete teardown?

 

[racerone]

There is a small cover on the side of the cylinder.-------6 small bolts 1/4" hold it on.-------Remove to look at the upper piston ring.

 

[simplydave]

dilemma, Looks like the powerhead has to come off the exhaust adapter in order to access the bottom screw on the cover plate. I guess it makes sense at this time to have it honed and any possible problems taken care of. The word I'm looking at is "rebuild". My dilemma comes in with still having a 35 year old motor, bright spot is cost, not so bright spot is something breaking all over again. What do you guys think?

 

[racerone]

????---The powerhead does not need to come off to remove bypass covers !

 

[simplydave]

sure looks like it to me. The bottom most bolt doesn't look accessible unless I take off the lower pan. I've already taken off the solenoid, the power pack and moved most of the wiring out of the way but I can't get a socket or a u joint socket on the bolt.

 

[racerone]

The bypass covers are on the sides of the block !-------6 screws on each cover.--Very easy to take off to look at pistons and rings.

 

[emdsapmgr]

The piston has a lot of slop between it's sides and the walls of the cylinder liner. You can move the piston around inside the cylinder with your fingers. (slightly) As you move the piston around, you can shine a light down the space to see the top ring. Usually you will be able to see the shine of the light on the stainless ring and can see if it is in one piece or not. Pulling the bypass cover off is another good alternative..

 

[simplydave]

got the inspection cover off and only used 3 semi bad words. The top ring looks ok, there is an approx 1/8 inch gap on the part that I can see. I tried to shine a light between the piston and the cylinder wall but can't twist my head down far enough to see between the lower pan and the bottom side of the piston. Any tips?

 

[boobie]

Get a small flexible mirror like a dentist mirror and try that.

 

[racerone]

You should not be able to see a gap on the piston rings when inspecting through the bypass cover.

 

[simplydave]

thanks racerone. I wondered about that, like I said the gap is about 1/8 inch mol and it's right at the port. I used a small blade screw driver to try and move the ring and it does move but only so far before I have no purchase on it. I guess it's time to think about rebuild or replace.

 

[racerone]

Piston ring gaps are positioned with locating pins.---That makes sure gaps are not near the ports.----These crossflow motors are easy to rebuild and will give many more years of service.

 

[emdsapmgr]

Pay attention to post #18. You should not be able to see the ring gap through either the exhaust ports or the intake ports. The ring locating pins are at 90 degrees to the drilled ports. If you can see the ring gap, the ring is either broken or has rotated due to a missing pin. In any case, the ring ends can catch on the port openings during rotation-causing disastrous problems.

 

[simplydave]

thank you very much both you racer and emd. I'm in the process of deciding whether or not to turn this into a core for a new block or have it done locally. I'm in west central Florida, any recs? Don't know if I can ask that but what the heck. Local (well not really) the rebuilt is about 2300, I definitely don't have the where with all to do this my self and I don't want to put 5 or 6 K out there presently.