To make a long story shorter, I've got an '88 L98 with a botched rebuild by the previous owner. The engine has ~2000 miles on it since the "rebuild". I accquired the car back in April, (when it had about 1200 mi. on the engine) and noted that the car was burning large amounts of oil. I only observed big blue clouds of smoke on hard acceleration, but from the smell of the exhaust and look of the plugs it was getting a bunch of oil in the chambers most all the time. It didn't, however, smoke when it started, cold or warm. The car ran good and smooth, got respectable gas mileage, and seemed to have lots of power.

Fast fowrard to today: After putting 700 miles more on the engine with no change, I've pulled it and disassembled it. Now I'm trying to identify what was causing the oil consumption so I can fix it and put it back together. The cylinders didn't show any wear, since the rebuild. The engine has been bored .030, but doesn't show the cylinder-wall finish that I think it they should. Here's the real question: The engine was assembled with Sterling H423NP30 pistons that have the deep oil ring grooves. The ring set used was a Sealed Power E377X which is for a shallow ring groove piston. Would excessive back-clearance behind the oil ring cause excessive oil consumption? Sealed Power, as well as Hastings, says that once the difficulty of installing the shallow rings on the deep-groove piston is overcome, they should seal fine. Everyone else I've asked seems to think otherwise.

Considering some of the other shoddy workmanship I've uncovered (that I won't go into here) and the questionable finish on the cylinder walls, I'm wondering if the block was machined properly. I know I need to mic it and find out, but right now the block is sitting in someone else's shop, and I'm just asking for opinions. I'll attach a close-up picture of the cylinder wall finish. Most of the "round-and-around" marks from the boring bar are still visible--- it looks like the cylinders weren't honed much at all. I'm trying to decide on a strategy for putting this engine back together. I want to be sure it is right this time, even if it ends up costing me more than I planned on (which, of course, it already has).

What do you think of the deep-groove/shallow-groove thing? Is boring these blocks .040 oversize a bad idea on a ~300 horse motor? I feel like .060 compromises cylinder-wall integrity. A couple more questions: Can I install new rod bolts myself without upsetting the cap alignment? Should the roller cam & lifters be replaced on a 135K mile engine even if they don't look worn?

Thanks for any information!
Jason
(hope my pic works) [img]C:\MYDOCU~1\DCPICS~1\IMG_0971.JPG[/img]


[Modified by needanother1, 2:54 AM 8/29/2002]

 

Basically, you need to rehone and rering your engine...at the least. While you're at it, I would also replace all the bearings and check all clearances...basically, rebuild your engine again.

If the hone finish is too smooth, that'll cause the problem. In all likelihood, your rings never seated. Your heads however, are fine, (oil-consumption wise), based on the fact that you get no puff of blue on start up.
It's rings, my friend.

Just have a machinist check your block to see if you can just get away with a rehone job and no overboring. If you're lucky, you'll only be out the money for a new set of rings (DON'T reuse the old ones!!!), new bearing kit and gaskets.

Now would be an excellent time to change the cam if you weren't totally happy with the cam that was in there. There are lots of retrofit roller cams that reuse OEM roller lifters. (Wasn't the 1988 L98 a roller engine?).
Just the cam won't be much, as compared to buying an entirely new roller set up.

 

Definiately sounds like rings did not seat. Check the bore for size, taper, and roundness. If all checks out, hone it, install new rings, bearings, and cam if you want. You can install your own rod bolts, be sure to check the rod size(dia.) before and after, and follow installation procedures recomended by bolt manufacturer. If they say to resize/recon rod after installation, you only need to do so if your measurements(dia.) change. If you are considering to abuse it :D , it is usually very inexpensive to have the rods reconditioned at your local engine shop, and it is cheap insurance! The deep groove/shallow ring most of the time has no effect on oil use/consumption. I ran a DZ302 with the same situation and had no negative results, just make sure to install rings correctly and use quality brand! :cheers:

 

I don't have a new set of rings yet (trying to figure out just what I need before I start buying parts) and no bore mic, but last night I checked the ring gaps using the old rings. Top ring gaps ranged from .040-.050" and the seconds were even bigger :eek:. I think the machine shop that bored this block may have gotten a little crazy. The cylinders show no wear since the "rebuild": There's no step above or below ring travel.

What end gaps will you typically end up with for a good-quality, out-of-the-box ring set on a properly bored/honed engine? How about boring this engine (or maybe just honing) to 4.040? Would I be left with flexy cylinder walls? I'm not trying to build a race motor, but I want to be confident that I'm putting together a solid engine.

Jason