gearhdmilwright

On an earlier post, I asked one of the questions I asked was about an odd vibration at 2100-2300 rpm or so. The engine has less than 200 miles on it, so I wanted to throw out a few "what ifs". Sorry, this post is really long, but I'm getting desperate, and REALLY dont want to pull this engine again....

- I had the pistons replaced on the advice of my machinist (LONG TIME CHEV GUY/ RACER). The stock bores and pistons were nearly perfect, but the rings were looking pretty bad, and I was getting pretty bad blowby. (expected for a 200k mi. engine). We only replaced them because the rings for the stock pistons are metric (I checked it myself), and alone cost more than a brand new set of Speed Pros with rings.. The new ones looked nearly identical to the old, in that they too had the short skirts. Are there any guys out there who have had a vibe problem with new pistons on the externally balanced engines?
- The vibe almost sounds like a dead miss, and the car seems to not have the power I would expect. Idle is not perfect, but not as bad as I would expect if a spark plug were bad. They are fairly new, and look good. Would I get some sort of misfire code if plugs were the culprit?
-I understand that the TPI system is a batch fire deal, in that each bank alternates, firing all four on each side alternately. I am not entirely sure that I got all the injector connectors back in the original place, but as long as they are on the correct side of the engine , I thought it shouldnt matter.....no?
-The last thing I can think of is the torque converter. Just for fun, I had a very reputable converter builder in Portland, OR. modify mine to stall at 2000-2500 rpm. Maybe they got it wrong?
I've built a lot of Chevy engines, most really hot stuff, and never had a vibration like this. If it was carbed, I'd have this one licked. But the TPI throws a bit of a wrench in things in that I dont know what to expect if something's not right in the system. Any ideas?? Thanks!!!!

Vader

You've got it close. The TPI batch fire actually fires all eight injector simultaneously, and once per engine revolution (twice per cycle). In reality, the connectors don't matter, so long as they are connected somewhere. There is no sequence whatsoever.

Was the rotating unit balanced for the new pistons? Just checking.

Since the only other "wildcard" is the TC, and it was opened, I'd consider that as a possibility as well. Things happen.

gearhdmilwright

Thanks for the response, and the batch fire clarification. I think I have found the vibration.... I think it is indeed the converter. I disconnected the conv. from the flexplate and then ran the engine. Of course, it runs way funny (no flywheel effect), but no vibration. I would think that the conv. would act as a damper, and therefore the vibration would be amplified without it. Further, when I turn the converter by hand when unbolted, it makes a funny (not ha ha) gravelly sound, and will wobble up and down if I push it that way, indicating to me that maybe not only do I have a conv. problem, but possibly a front pump issue as well. Seems strange though, as the trans was behaving pretty well before the engine rebuild, though I removed the engine in the first place due to a "rod knock", which still exists after the rebuild. As I mic everything before I assemble an engine (and after dissassembly), and everything was at spec, I now suspect the trans as the culprit of my knock. Just goes to show that even a veteran mechanic / hotrodder can be wrong. So, back under I go to remove the transmission. If this fixes the problem, I'll post and let everyone know what it was. Still, if anyone has a suggestion, I'm open.......

Vader

If this is the 4L60E, you may be able to get by with a pump bushing and new converter. If you're lucky, the bushing (a normal wear item) is the only problem. Since the converter was pounding away at it, it's worth a look.

Check out Edge converters if you're looking for a replacement. At least take a look before you settle on your choice.

gearhdmilwright

Yeah, the converter I have is the stocker, that I had modified by Superior Converter here in Portland. I had it done while the engine was in the shop this time, so its basically new. Only cost 150 bucks to do, and should still be under warranty. If it doesnt work out, and I dont roll the car into the Columbia, then Ill check out the converter you mentioned.