Hey yall,i have a 97 s10 blazer 4x4.It quit going down the road at about 60 mph.i got it off the road and tried to crank it and it sounded like the battery was dead.so i got my other truck down there and tried to jump it off and it just sounded out of time,so i got it home and and pulled the #4 piston to tdc and my marks on the timing cover and the harmonic bal. was lined up.so i pulled the dis. cap off and it was pointing a half around out.. 90 degrees out.so i tore it down and looked at the timing chain and it had some slack but not alot.the gears look ok but heres what i have any clue about,the balancing shaft gears.the gear that goes on the cam,that fits in that dail pen like thing.is it suppost to have alot of slack around where the gear slides on to the pen or what?what do the put them on there for?????if yall can help it will help alot.....

thanks brandon

 

I have a 95 Chev Blazer 4.3L vortec that I am checking the timing chain on. It suddenly felt like theignition timing had changed when I was gunning it to get onto a highway. Suddendly felt like the timing had advanced, and the engine began to ping horribly with accelleration. When I finaly got home and checked theBase timing(disconnected the timing plug on PCM),itlooked like the timing had changed pretty far. I had assumed my timing chain had slipped a tooth, since the distibuter was still buttoned down tight. So I started to tear into it, and found the timing gears to be perfectly lined up. I also noticed that my balancer has TWO marks on it ~90deg appart.I would like to know what that second mark is for??? My factory manuals don't mention anything about it...Has anyone replied to your post, or did you figure anything out. I would like to learn more about this...

As far as your question about the pin on the camshaft, I believe that the pin is only for gear to camshaft alignment purposes, and doesn't need to fit tight. The 3 bolts on the cam gear are what square the gear to the cam, and the pin is only there as a "marker". My chain also has some slack, but I think that is also normal, as would need to have a huge amount of slack to be able to slip a tooth.

thanks,
Mike

 

hey,i havent found out nothing about mine either.i have seached everywhere online and in the book to find out about those marks.i still cant get mine in time i dont understand.if anyone knows how to time 97 s10 blazer 4.3,it would help alot.....
thanks brandon

 

It took a while but I found something for you.
Rotate the number (1) cylinder to Top Dead Center (TDC) of the compression stroke. The engine front cover has 2 alignment tabs and the crankshaft balancer has 2 alignment marks (spaced 90degrees apart) which are used for positioning number 1 piston at top dead center (TDC). With the piston on the compression stroke and at top dead center, the crankshaft balancer alignment mark (1) must align with the engine front cover tab (2) and the crankshaft balancer alignment mark (4) must align with the engine front cover tab (3).


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Any luck?
Did my pm help?

 

My factory manual says that the #4 cylinder needs to be at TDC in the compression stroke when the timing gear marks are aligned. Do the #1 and #4 cylinders hit TDC at the same time, but one is in compression and the other is in exhaust??? I did notice that my mark on the harmonic balancer is lined up to the mark on the timing cover as well. So I am a little confused about the #4 vs #1 thing...

 

I have never heard of a motor being aligned to TDC #4... That is just weird... I'd have to look at a cam and crank to figure out if they are both at TDC compression at the same time... But I don't think they are...

 

My Blazer is running great again, and I learned a couple of things along the way. First off, my problem was with the pickup coil in the distibuter, and that's what caused the funky change in my ignition timing. When I think back on the symptoms now, it makes perfect sence. I was notcing for some time that my Blazer was not firing well at high engine RPM. When I would pass someone, I would notice slight cutouts, and sometimes I would hear significant pinging as it shifted to the next gear in full throttle. Since the pickup coil was starting to fade, it was not sending a clean signal to the computer, especially at higher revs. The computer did it's best to deal with the weak signal, but it effectively over advances the timing.It finally got to the point where the signal was weak enough thatwas effecting lower RPM's to the point where the computer was trying to compensate with timing changes that made the truck run horrible. When I checked the base timing (disconnected the timing bypass plug by the PCM), the mark had shifted, and I am assuming this had somthing to do with the weak coil as well. Before I tore into the engine to check the timing chain, I tested the pickup coil as per the factory manual. The problem is that those tests only check the pickup coil for continuity, and for shorts. The coil measured 1k ohm (middle of spec) and was not shorted to ground, so I thought I was good. The problem was with the perminant magnet strength had weakened over time. Therefore, when the coil would pass by the magnet, a lower voltage was induced. There was a big differance in the magnet strength between the new and old pickup coils. I purchased a aftermarket rebuilt distributer from Carquest, and the pickup coil is also a slightly differant design. My truck now runs like it did a few years ago in the high RPMs, and has really good power through the entire RPM range without any pings.

As for the timing marks on the timing gears. The timing marks on the gears are indeed lined up when the #4 piston is at TDC Compression stroke. (#4 is 180deg from #1 on the distributor firing order, and 360deg on the crankshaft). Therefore the ignition timing mark on the harmonic balancer will be lined up when the timing gears are lined up, but the distributer rotor must point to the #4 position, not the#1. I also did notice the my new timing chain was fairily tight and the old one was pretty loose by compairison, but it would have to be really, reallyloose to slip a tooth. I have 158000 on my truck.

The harmonic balancer has two marks on it about 90deg apart, so you can check the timing from under the vehicle as well as from above, as there are two marks on the timing chain cover that they must align too, as shown in Chevy Lover's picture above. Thanks for that by the way... I'm still trying to figure out where you got that.