Burning oil then low compression

[chris90gsx]

My 90 GSX with 100k miles was burning oil under hard acceleration for about 2 months and was possibly doing it during other conditions, but I could not be certain. I have a brand new head on with new valve stem seals, a fairly new 16g (1 year old), and timing is right on. I am pretty sure the rings are worn and need replacement. Then I started losing compression the other day and the car will not start. Did a compression check and found cyl 1 to be at 60psi and cyl 4 to be at 90psi. I didn't bother checking the rest as those numbers alone were low. Could this be anything else besides the rings? I have bought a good 6 bolt block and plan on just swapping that over instead of doing just a ring job. Besides, that will give me an extra block to work with on the side. Thanks for your suggestions and help in advance.

 

[ITSME4G63]

you might have some bent valves, or valves that have married the pistons

 

[WhiteCloud]

Looks like you're going to have to pull the head either way, so you can check bent valves too.

 

[chris90gsx]

Finished up most of the work today. I got a good 6 bolt block from a guy locally and swapped this shortblock over for use in my car. I pulled the head and everything was in tact with no bent valves at all. Block looked good and head gasket was not blown and had sealed very nicely from when I replaced it back in the early summer when I did my timing belt. Cam timing marks were all right on and everything looked fine. I did notice some grit on the top of the pistons besides the normal carbon build up...possibly pieces of deteriorated ring? It must be the rings at this point, which was what I had thought all along since I have a new head, 1 year old 16g, and just replaced alot of parts. What worried me was that compression seemed to drop all of a sudden. Although I hadn't done a compression check near the time that the car stopped running, the car was showing no signs of failure or struggle, just burning oil under hard accleration. I will be pulling the block apart to take a look. Thanks again for the suggestions and replies.

 

[dynatos]

careful: if you fried your piston rings then make sure it didn't blow the welds on your intake

.. if anyone doesnt know what the heck i'm talking about there, don't pay any attention..



Did you have any problems like this before putting the rebuit head on?

 

[chris90gsx]

! Quoting F&F for those who didn't get it :laugh:

No problems before with putting the rebuilt head on. In fact, the head was not necessary when I did it. The dowel pin on my intake cam snapped some how and the cam gear was floating in a sense. It retarded intake cam timing by 3 teeth but did not cause any damage whatsoever. I noticed that the marks were off and when I went to reset them, I could not get the cam marks to line up so I assumed I had bent a few valves. Got the new head and transferred my old cams and found the same problem. I took an extra cam I had laying around and held it above the head in the aligned position to compare the position of the lobes and found that they didn't match oneanother. I undid the cam gear bolt and sure enough it was just freewheeling. Not sure how that ever happened but it did not damage any of my valves or cause any problems beside a bad idle. Possibly a valve guide caused a valve to stick or something. After changing over to a spare intake cam I had the marks lined right up and the car ran excellent and continued to even when burning the oil a few weeks ago. Hopefully I will get some time this weekend to pull the pistons and see what caused the compression to leak.

 

[chris90gsx]

Well I got everything put back together on the car today and fired it up. I am hearing some valve tap and will have to further investigate tomorrow. Cam timing marks are dead on and the head is a rebuilt one with about 5k miles on it maybe. I did swap in a block that was "supposedly" rebuilt 25k miles ago so I am thinking that it was possibly decked too much (possibly blown headgasket before) and might not be allowing adequate piston to valve clearance. I'm kinda stuck between a rock and hard place as I am uncertain as to how to approact this to determine what the fault is. I will pull the valve cover tomorrow and see if I see any springs that look compressed but the car ran and idled fine otherwise. I let it run for about 2 minutes and then turned it off. I checked compression for the second time after the valve tap to make sure nothing went south, and compression did not change. Before it was showing roughly 120psi across the board, but I think the compression gauge I borrowed from a friend was not working properly as it leaked compression immediately and would not hold a reading. I will be getting my good one back from someone who is borrowing it from me and recheck the numbers. I guess I will also check the cam gears again to see if a dowel pin sheared since it has happened before. Otherwise I don't know what else to do. Any suggestions or comments on the situation to get me going for tomorrow? Thanks again.