91' larson, 4.3 timing issue

[thegoat86]

This should be the last of the gremlins.... hopefully. I replaced plugs and wires, noticed two wires were wrong. And further noticed the distributor was 90 degrees off. So...... I found #1 TDC compression, dropped distributor in correct alignment based on mercruiser manual, (this is thunderbolt IV ignition) Got it running, then tried to set base timing. Now all that sounds great, but my motor does not have degree timing marks. It has a v-notch. The breather cover states 8 degrees BTDC. When I time the motor to the mark, it runs rough and does not rev. If I time a half inch behind the mark, the motor revs and sounds great. I am going old school on this one by setting timing by vacuum on the water under load. But would love to have input. The intake and carb were replaced by the last owner to a four barrel setup. FYI

 

[alldodge]

This should be the last of the gremlins.... hopefully. I replaced plugs and wires, noticed two wires were wrong. And further noticed the distributor was 90 degrees off. So...... I found #1 TDC compression, dropped distributor in correct alignment based on mercruiser manual, (this is thunderbolt IV ignition) Got it running, then tried to set base timing. Now all that sounds great, but my motor does not have degree timing marks. It has a v-notch. The breather cover states 8 degrees BTDC. When I time the motor to the mark, it runs rough and does not rev. If I time a half inch behind the mark, the motor revs and sounds great. I am going old school on this one by setting timing by vacuum on the water under load. But would love to have input. The intake and carb were replaced by the last owner to a four barrel setup. FYI

Need to look close at the harmonic balancer to see if the markings are on the balancer it self. If not you have two choices, a timing light with an advance or timing tape. The cheap and easy is timing tape, just need to measure the diameter of the harmonic balancer. I think it should be 6.75 but measure to make sure. Then pick up some tape and stick it to the balancer.

Here is MSD set of 8 from 5.25 to 8 inch
http://www.summitracing.com/parts/msd-8985/overview/

 

[achris]

The notch on the cover and in the balancer line up at the TDC point. As AD said, you need either and advance timing light or a 'timing tape'.... I'm aware of the 'old school' method, but on these engines, that doesn't work.... You'll end up with the timing too far advanced and be blowing holes in the pistons....

Chris.......

 

[thegoat86]

Buying new balancer. I cleaned some rust off and saw some marking. Guess that would be the timing marks. Needed replacing anyways, the rubber looked to be coming out.

 

[thegoat86]

Silvertip; commented on my other thread about a knock sound coming from my motor. "Before you do anything, do lots of reading on the issue regarding balance shaft noise due to the bearings it runs in. This noise was very common on the balance shaft motors but had nothing to do with longevity of the motor. If yours is not a balance shaft motor then further investigation as to the noise is obviously necessary. My experiences with this noise compares it to pre-ignition (spark knock for old-timers) at various rpm. GM had a kit to take care of this but other than being an annoyance, most folks chose to live with it. I once bought a '92 AWD Chevy Astro van with about 50K miles on it. At about 60K the slight balance shaft noise appeared and was the same at 150K when I sold it"

I have a knock that starts around 1000 RPM, I thought it might have something to do with timing. So his pre-ignition idea sounds right to me. But, my friend is telling me its a mechanical knock like a wrist pin loose. Motor runs great and strong. But that doesn't mean much. What is balance shaft motor? I am replacing the harmonic balancer if that is what he is talking about.

 

[bruceb58]

Later 4.3L engines have a balance shaft that sits underneath the intake manifold. You can see it in this picture. If the engine in your boat is original, you don't have it. Balance shaft engines didn't go into vehicles until 92 and likely not into boats until 93 or later.

 

[thegoat86]

Figured it out. On non-balancer motors the timing cover is level with the top of the water pump ports, on balancer motors it goes up another inch and a half. Checking momentarily. Why would this cause a very audible knock? I guess the best way to tell would be to pull the balancer gear and rev the motor.

 

[thegoat86]

Yes my motor is a balancer motor. Guess the person I bought it from changed the motor. Now, would I hear an audible knock from that? very loud around 3000 RPM. And am I correct in assuming that if I pulled the chain and removed the drive gear from the balancer, that I can determine if the noise is from there?

 

[Scott Danforth]

use a stethoscope. you may simply have balancer noise which is somewhat common with balance shaft 4.3's. also do a balance test. the 4.3 with balance shaft will run smooth on 5 cylinders. you could have a bum plug

 

[JaCrispy]

You can mark the 8* BTDC using some geometry. If the radius of the balancer is 3.375" and you need to find 8*, measure back from 0 (TDC) 0.471"

http://www.handymath.com/cgi-bin/arc18.cgi?submit=Entry

 

[thegoat86]

Balancer is around 6 1/2", I will check and try that. (awesome find ja)

 

[thegoat86]

use a stethoscope. you may simply have balancer noise which is somewhat common with balance shaft 4.3's. also do a balance test. the 4.3 with balance shaft will run smooth on 5 cylinders. you could have a bum plug

How is this test done? I unplug a spark plug wire and see if the motor shakes? Please elaborate. Gracious

 

[thegoat86]

couldn't wait for reply. I tore into the front of the motor, found the timing chain one tooth off. Reset chain, took off the cog that runs the balancer, reassembled the chain, and test fired the motor. I have a little valve train noise because the timing is still a little off now that I made the tooth change, but the loud knock is gone all through to WOT. So, do I need to run this balancer? I will try to align the balancer with the timing chain and try again. Assuming maybe it was off like the chain. The person who put this motor together was def a hack.

 

[achris]

Yes, the balance shaft needs to be set up to the camshaft correctly.You'll find alignment marks on the balance shaft gear and the camshaft gear....

Chris........

 

[thegoat86]

Ok, done as indicated in drawing achris. The loud knock is still there. It is def the internal balancer. But now its a little less obnoxious. I have a small oil leak where the timing chain cover meets the oil pan..... Arghh. At least all I have to do now is drop the pan and re-gasket. Just time consuming.

Wondering if I can just keep the balancer gear out and run it. I am only keeping the boat another year or so. Then moving up to a larger cabin cruiser. As this is my starter boat, it is not the nicest. I did not want to destroy a new boat while learning. So, I am probably taking it to a donate your boat place in a year or so. Not reselling.

So, with all of that info in mind, what would be the popular vote on disconnecting the internal balancer? (it is a very loud annoying knock at speed. kinda like having a hammer drill going while you drive)

 

[achris]

...Wondering if I can just keep the balancer gear out and run it....

No... The blocks without the balance shaft needed a special fluid mounting to reduce the vibration transmitted by the normal rubber mounts. GM put the balance shaft into the block for a reason... 90 degree V6... That's why (inherently unbalanced).... And a 60 degree V6 doesn't need them....

 

[Silvertip]

You seem to be coming up with symptoms that don't make sense. Having valve timing off one tooth does not create valve train noise. The valve train works the same way regardless. The valves are just not operating at the correct time. Balance shaft noise is not typically a hard knock unless there is extreme wear. As I pointed out earlier, it was more akin to spark knock/pinging/pre-ignition so more of a rattle than a knock. It was also not an across the rpm band noise. In my experience it was a low rpm part throttle noise and was not noticeable under load or at idle. Since you ran the engine with the balance shaft drive gear removed and didn't hear the noise, then you need to inspect the bearings and the gear for excess wear and end-play. Wrist pin noise and piston slap can be isolated as Achris indicated. Pull one plug wire at a time. If the noise is isolated to one cylinder, that cylinder will go quiet when the plug wire is pulled. Those noises also appear deeper in the block whereas valve train and balancer noise is higher up.

 

[Bondo]

couldn't wait for reply. I tore into the front of the motor, found the timing chain one tooth off. Reset chain, took off the cog that runs the balancer, reassembled the chain, and test fired the motor. I have a little valve train noise because the timing is still a little off now that I made the tooth change, but the loud knock is gone all through to WOT. So, do I need to run this balancer? I will try to align the balancer with the timing chain and try again. Assuming maybe it was off like the chain. The person who put this motor together was def a hack.

Ayuh,.... Considerin' yer pullin' the pan to regasket it,....

I'd check the rods, 'n mains at the same time,.....

If the guy that assembled it can't get the timin' marks right, I'd be concerned the bearin' clearances are also suspect,.....

 

[thegoat86]

Silvertip, motor was timed today and runs great now. Nice idle, very smooth. Knocking noise was def internal balancer. It is all through the power band. Motor did not knock at all when balancer was disconnected. I agree with excessive wear. But am not going to change it.

Bondo, yup yup. I agree totally.

 

[thegoat86]

Guess the guy only messed with timing chain and dist. This may be a reman longblock with the parts swapped. Everything checked ok, no wear visible. Looks like a new motor to me. I even popped off a cap to check bearing wear. Since The balancer is under the intake, I may decide to take a peek and make sure its not something silly like the wrong intake was put on from an earlier vortec motor and it may be hitting the underside slightly, or tapping the windage tray if there is one. Which could have been installed improperly. I am not putting anything past this motor now.

Resealed and ready to go now. Purrs like a kitten, but taps like a hammer drill. The best of both worlds I guess.