mattgadient.com

Sprint valve burnt because the valve was not closing

The title says it all. For the benefit of the search engines, I should mention that this should apply to most 1.0L 3-cyl Geo Metro, Suzuki Swift, Pontiac Firefly and Chevrolet Sprints made around 1991 (89-91).

Basically I can sum it up by saying this. We had an engine that started to perform badly and over the course of 2 weeks really took a hit to the point where it didn’t even want to go over 90 km/h. It seemed like the timing was retarded, and would sputter, cough, and had terrible performance at low rpm’s. I’ve read through the teamswift.net forums often enough to know that these engines are prone to burnt exhaust valves, so we figured that was probably the cause. A compression check verified this.

We pulled off the head and took a look. Sure enough, there was a flat section where the valve wasn’t sealing any longer. Seeing’s how we had a parts car and weren’t looking to feed any more money into this one, we pulled the head from the parts car which fortunately still had 1 non-burnt valve left on it (you can guess why it became the parts car). We grabbed the good valve from the parts car and swapped it with the bad one from the current one. Since we already had the head out, we took the opportunity to lap all the valves which was probably a good thing, since most weren’t in the greatest of shape. Once it was all said and done, we oiled everything up and put the head back together.

Before bringing the head back to the car, we thought it might be a good idea to turn over the camshaft a few times just to make sure the valves were all opening and closing properly. It’s a good thing we did, because the exhaust valve we replaced wasn’t closing all the way.

I’ll be honest. We were a little perplexed. Sure, it was a used exhaust valve we were using, but it still had a lot of wear to go. Our first thought was that somehow it was a longer valve than the others. We pulled everything apart and compared it to the others… it was the same size. One thing we did notice was that some of the lifters had leaked out the oil and when you pushed on them, they had some play (a springy feel). This happened because we didn’t take the steps you’re supposed to to keep the oil from running out. Some had managed to retain their oil though and still felt solid. The lifter on this exhaust valve was one of them. We decided to try swapping the lifter for another one that had lost it’s oil (felt springy). We tried a few actually before we found one that did allow the valve to close and seal.

This got us thinking… the original valve must have worn enough that it didn’t seal. Either the hydrolic lifter didn’t adjust itself (possible), or it had reached it’s limit, at which point not being sealed caused the valve to burn (probable).

At this point, we came up with 2 options:

  1. Put the engine back together and hope that it takes a long time for the valves to wear to the point of burning, or;
  2. Grind off a little bit of the top of the valve stems.

We chose #2. If we had replaced all the valves, then maybe we’d be fine, but since we were determined not to sink any money into this project, we decided to grind a little off the top of every valve stem.

There are a few things to keep in mind when doing something like this… First of all, if you grind off too much, the valves may not open very much. The hydraulic lifters should compensate to a degree once they’re pumped up with oil, but you still have to be careful. Second, you want to make sure you don’t end up grinding at an angle, because the lifter should have pretty even contact with the top of the valve stem. Third, you have to be careful not to grind too close to the groove in the valve stem where the keepers are. Not only might bad things happen if the lifter starts smacking the keepers instead of the valve, but if you manage to grind off that much, the valves may never open. Fourth, you should probably sand the end of the valve after grinding it, just to make sure you have a smooth area for the lifter to contact, and to make sure that you dont have jagged edges which might break off when the engine’s running. Finally, after it’s been done and the head’s back together, it’s probably a good idea to rotate the camshaft and watch the valves to make sure they’re all opening and closing fine.

As it turned out, the grinding seemed to work quite well. The valves all opened and closed fine, and the camshaft turned quite easily now (mainly because most of the lifters needed to be pumped up). We reassembled the head, and put everything back together. We risked re-using the same head gasket with some high-temp gasket glue and reused the stock head bolts. It happened to work well for us, but no guarantees if you try to do the same. The first start was met with some loud clackity-clacks, but once the lifters pumped up, it ran very smooth and quiet. It runs and drives incredibly smooth, and if we end up with a burnt valve down the road, at least we’ll know the cause isn’t a valve that’s worn so much that it stays open.

A few final thoughts, things to note, and things to ponder:

  • based on what we experienced, I wouldn’t be at all surprised if many of the burnt valves on these cars happen simply because the valve wears to the point of not sealing.
  • new valves are probably a better option for most people. I would assume that because a new valve will be thicker, it’ll seal if: a) the lifters are working properly and b) the head isn’t terribly worn where the valve meets it.
  • as far as grinding the valves goes… possible issues down the line..? I wouldn’t really think so, but it’s hard to say for sure. Since we didn’t take any measurements and simply ground them by eye, we’re totally reliant on the hydraulic lifters to adjust to them. Also, it’s possible that the integrity of the valve’s been compromised. For all we know, it might split, crack, shatter, or do something else funky some day. I think it’s unlikely, but only time will tell.
  • we swapped around a lot of the lifters, and exchanged the ones that still felt solid for the ones that were “unpumped” from the parts car. You’re not really supposed to do this. You’re supposed to number them and put them back in their original locations (unless you’re replacing with new ones). Again, it could cause issues down the line.
  • things turned out well for us – that doesn’t mean they will for you. Always follow the recommendations layed out in proper repair manuals. Of course if you’re looking to save a few dollars and have some parts lying around, maybe this post will help you. Just be aware that I’m disclaiming responsibility for anything and everything ranging from an engine malfunction/failure to your car exploding and taking everything nearby with it. You’re on your own.
  • finally, if you’re looking to do things the proper way, there’s a gentleman from the teamswift forums named Mike Cove who supplies certain parts at some very good prices (at the time of this post, $30 for a set of 8 headbolts/washers, valves starting at $6 each, and sells camshafts, heads, etc). He’s highly respected on the teamswift forums, seems to be a really smart guy, and I’ve bought from him in the past. And no, I don’t make any money/commission from any of his sales (I’m sure he doesn’t even know who I am). His prices do seem to be pretty good though (although you may want to check your local stores to compare), and from what I gather, the parts are pretty good too. You can find his site at http://www.teamswift.net/3tech or you can simply browse the forums there.

0 Comments

 | Leave a Comment

    Leave a Comment

    You can use an alias and fake email. However, if you choose to use a real email, "gravatars" are supported. You can check the privacy policy for more details.

    To reduce spam, I manually approve all comments, so don't panic if your comment doesn't show up immediately.