85 250SX help

[drsung]

Well, here is an update... I got the cylinder head cover off tonight. I have attached a picture. From what I can tell everything looks normal so I will have to keep going. The cylinder head will be removed next.

The only new development is that I noticed the banjo bolt was broken off in the head cover, not just missing. And, I am fairly certain the head cover was NOT removed recently. So, I am now thinking either he tried to take off the banjo bolt and it broke or he tried to get the head cover off and couldn't and he broke the banjo bolt putting it back on.

I want to ask this one more time because I am trying to understand and wrap my head around it. Why would the broken banjo bolt not cause a loss of compression? Seems like that would give the air a path to escape.

My new banjo bolt should be here tomorrow so I will work on getting the broken bolt out of the head cover before I remove the head.

[Dirtcrasher]

I have an ES parts motor; I forget what I gave to Loius Mielke but anything you need like that bolt, I believe I have.
Just post it here or PM me - DC

[Frankencelery]

I want to ask this one more time because I am trying to understand and wrap my head around it. Why would the broken banjo bolt not cause a loss of compression? Seems like that would give the air a path to escape.

Because compression takes place in the cylinder, and the oil passage doesn't lead to the cylinder. It leads to the top of the head. Make sense?

[Flyingw]

The thing to remember here is the oil is pumped out of the tranny case by the oil pump up to the top of the head and in to the CAM journals. The CAM does not have bearings. The oil that is pumped directly in to the journals forms an oil bearing. The oil leaving the CAM journals leaves the head and back down to the tranny by way of the CAM chain chimney where the cycle is repeated. Loss of compression has nothing to do with the broken off banjo bolt. The banjo bolt is a 7mm fine thread bolt so its only supposed to have about 12lbs of torque. Not much more than snug. Somebody probably broke it off by over-tightening it because it was leaking. It sounds like the top end needs to be rebuilt. Lap the valves and replace the valve stem seals. Bore the cylinder to the next size with a new piston, rings, and gaskets will give you a fresh top end good for many years.

[drsung]

Thanks for the education and clarification guys! I am hoping to have time after work today to take the head off.

[drsung]

Another update on my saga... I got the head off and it looks like both the intake and exhaust valves are bent. If I rotate in the valve guides there is quite a wobble on both of them. I have attached a picture which show some good marks of the valves hitting the top of the piston.

Nstyle73 - I'll take you up on that set of valves if they are still available.

Now for the next question... Could valve adjustment be off enough to cause the valves to hit the piston or do I have cam/cam chain problem?

[Flyingw]

No way to tell at this point since the head is off now. It could one or both. From here I'd say replace the CAM chain. They do stretch. As far as the valves go, using used valves is ok but just be sure to LAP then in and replace the stem seals and if were me, I'd have that cylinder punched to the next size with a new piston. Might as well since its all apart anyway. That will refresh your top end for a long while and since the clutch is apart, put some fresh plates in it. Might as well do it right and not worry about it for a while.