Sorry if this is a dumb question. I have read some other threads where people say an early knock can be repaired and others that aren't clear.

My 2.8 knocks, but only between 2500-3000 rpm. Once I open the bottom end to see how it looks, what will tell me if I need a rebuild or if I can just replace the crank bearings (if it's the main - and if that's possible).

I looked at the oil twice now and there are no signs of metal in the drained stuff. Perhaps she can be saved.

Am I totally screwed regardless?

Thanks for the help. I haven't had any luck finding another used block locally.

Cheers!

I'm not sure what kind of knocking you are talking about. If you mean a knocking sound that is like marbles bouncing around inside of your engine, that is knock from a lean A/F mixture causing your pistons to vibrate in the cylinders. That is usually caused by plugged or very poor firing fuel injectors.

I have not heard of an engine that only spins a bearing in that rpm range. Usually they will spin them at idle and if they are not too bad, may stop spinning them at a higher rpm. If that is the case, then you may be able to do a temporary fix by just replacing the bearing. That is a crap shoot. It may work for the next 100k miles or it may spin again the next day you drive it.

There are other kinds of knocking also such as I've heard transmissions knocking when the bearing preloads are too loose. It is hard to distinguish a transmission knocking from an engine knocking unless you place a hose or a mechanics stethiscope right up to it.

Saxman, how many miles are on this engine? When I was looking for a GT, I went and looked at one in Ohio. Started it up, everything was fine, took it out for a test drive on the highway, everything was fine. I turned around in a farm drive, and as I headed back, while accelerating (and not hard), it started knocking about 2500RPM until about 3500. We took the car back, pulled it into the garage, and tried to find the source of the knock. It sounded very much like a rod knock, and as I was about 700 miles from home, and had no way to get the car back home except to drive it, I passed on it. The owner later pulled the engine and put a different one in the car, and then tore down the original engine. Turned out it was a worn timing chain. It was stretched badly enough that it was hitting on the side of the timing chain cover. Why it only did it between 2500-3500 RPM, and not at a lower or higher RPM, or why it didn't jump a tooth or two, is beyond me, but John, the owner, said that it was very apparent, from looking at the inside of the timing chain cover, that is what was happening. Perhaps you might have the same problem...worth looking into.

Doug - thanks for the reply. The knock is not like a bunch of marbles. Here is the video.



I had another thread about this here - https://www.fiero.nl/forum/Forum2/HTML/090516.html

Thanks, litespd! I was hoping to hear something like your post. I hope this is the case.

This engine was rebuilt just 5,000 miles before I got it. I have the receipt for it. It did sit for a few years before I got it, though.

Here is what the timing chain looks like on the 2.8 now. I can see some dark rings around the inside of the cover, but it just looks like dried oil in the chain pattern. Is this too much slack?



Here is what the timing chain looks like on my new 3.4. Much tighter than the old 2.8



Thanks again. What you mentioned is just what I was looking for. It seemed really strange that it would only knock at certain rpm and only under a light load.

[This message has been edited by Saxman (edited 09-04-2008).]

Sounds like a rod or crank knock caused by worn bearings. A complete teardown and rebuild is most likely required. Get out the stethoscope and start listening but first check the chain as it could be the problem.

------------------
87GT - 3800SC Series III engine, 3.4" Pulley, N* TB, LS1 MAF, Flotech Exhaust Autolite 104's Custom CAI 4T65eHD w. custom axles
87GT - 3.4L Turbocharged engine, modified TH125H
" I'M ON THE LOOSE WITHOUT THE JUICE "

[This message has been edited by Dennis LaGrua (edited 09-04-2008).]

Most of the seasoned pros will say that you have to tear the engine completely down and rebuild it from there. In my case I had a rod knock between 1500 and 1900 rpm on very light load and heard it more towards the end of an oil change cycle.

I figured that $50 bucks for rod bearings, oil, filter and a gasket I really didn't have much to lose so I went for it. It's been 5 or 6 years now, still running like a champ.

The test was to disconnect one plug wire at a time and see if there was any change in the noise. In my case, it was #4 cylinder rod that was the culprit. I replaced all the bearings and #4 really didn't look all that bad. It took about 5-1/2 hours to complete, not too bad compared to a full rebuild.

My $0.02 worth for you.

Good point, Jetman. Since the cradle is already out, I can't try your plug wire removal method. I'll just have to look at each bearing closely. Thanks!

Engine out of car. drop the pan then it's Plasti gauge time. Oh, and read your spark plugs. Do they look like you're running lean? Fuel can gum up injectors when you let an engine sit too long. Good luck.

quote Originally posted by Saxman: So you guys think that bit of play in the timing chain is OK? I don't want to leave a bad one on there.

A 3 piece set is $30.00 or so. Change it and scratch it off of your list if "Maybe"'s Flip the engine and gauge all of the bearings but make sure each bearing half and the crankshaft is DRY all of the way around before you use the Plastigauge. Then scratch it off of your list also.

Before you can fix what is wrong, you have to know what is right. Then move along to the next item
Joe Crawford
Texas

Thanks for the advice (as always), Joe. Sorry I couldn't help you with the lower seat cover.