Effect of MisMarked Damper +5 degrees?

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jimmyray

jimmyray

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I was recently mocking up my 408, after I recently tore it down. With the crank back in and damper installed, with a dial gage, I determined true TDC to double check the damper marks. Low and behold, the damper was off by 5 degrees! Effectively increasing whatever i thought my timing was by 5 degrees. Since I thought I was running at 34 degrees total, I was actually at 39! Although I never heard pinging or detonation noises, even with 87 octane, this could not have been good.

My motor combo was:
408 Eagle cast crank, Eagle rods, KB Hyper pistons, all from Hughes
9.6:1 compression
93 Octane gas
mild port/polish on Edelbrock al perf heads, closed chamber, fresh valve job
M1 single plane airgap with gasket match (heads too)
Carter TQ - .102 & .161 jetting, 1.5” primary
Comp roller .544/.541 236/242 110 centerline
FBO ignition, ditributor curved to 16 inital, 34 total @ 2900 rpm
Hooker comp 1 5/8" headers (dented bottoms on driver side, naturally) 3" collector
3" pipes into/out of welded Summit 3" mufflers into a-body tips
4000 9.5” Dynamic Convertor
727 manual reverse
3.73 sure grip in a narrowed Dana

Race Weight – 3400 + 200 driver = 3600 lbs total


The best I ever got out of the combo was a 12.13 @ 110. By the time I took it apart, after 130+ runs and 6500 miles, the blow by was enough to push off the EGR breather and blow oil out of the dipstick tube, and it was losing water bad.


Thoughts?





BTW, the Damper was the summit $89 job.

ScreenHunter_01 Dec. 13 20.14.jpg


ScreenHunter_02 Dec. 13 20.16.jpg
 
nice find im sure if every one checked,,most would be off,,,to many variables,,, crank key,,,timing cover markings,,,dampener stamping,,
 
Make a nice mark on your cover for true TDC.

Was the 35 (39) degrees you had before where the engine gave you your best ET? If there was no sign of detonation (tops of rod bearings worn to the copper), I would put it back there as a starting point. Next test and tune day I might play with less timing, to see what happens just in the interest of science.

Ever figure out why you had so much blow-by? Rings? Blown head gaskets?
 
With the combo you had I dopnt think 5° did much of anything. The static compression was a little low for the cam so it would be sluggish there. And the convertor is high for a mild geared 4" arm engine adding to the soft lowend. The blow by is more the result of poor bore finish and ring seal. Just for fun... Did the machinist (or yourself if you assembled it) measure the side clearance on the rings? Too much side clearance (not end gap, but the clearance between the ring and the ring land) will also let a ring flutter and lose it's sealing.
 
Interestingly enough, the front rod bearings (1 & 2) were in fact worn to the copper, with the others showing wear as well.

Did not check for ring to land clearance, first I have heard of that.

Interestingly enough, I made a run a while back, suspected the timing, and double checked it. Since the bolt was not tight, timing had slipped to a 24 degree reading (actually 29 degree!) I set it to the correct 34 (actually 39) and saw no difference in ET. I thought it was odd at the time, but it makes sense now. As a result, I have never had the timing anywhere near the reccomended spot by KB, which is 32-34. I have only ever ran the car at 29 (by accident), and 35 to 40, which i thought was 30-35. Car did seem to like the 30 (actually 35) better.
 
moper said:
With the combo you had I dopnt think 5° did much of anything. The static compression was a little low for the cam so it would be sluggish there. And the convertor is high for a mild geared 4" arm engine adding to the soft lowend. The blow by is more the result of poor bore finish and ring seal. Just for fun... Did the machinist (or yourself if you assembled it) measure the side clearance on the rings? Too much side clearance (not end gap, but the clearance between the ring and the ring land) will also let a ring flutter and lose it's sealing.
Click to expand...

I was also thinking that is a lot of converter for that motor. Could use a little more compression too.
 
Generally bearing wear is a sign of oiling issues. Not timing. Loss of bearing crush without showing wear on the bearings could be timing. I'm not sure what crank you used or what the clearances were originally. But if a few bearings were worn I would be suspect of the journal finish on those journals rather than the oiling system as a whole. If you crank was simply re-used you will want to make sure there is no taper and the clearances are right. The typical stroker setup with closed chamber heads and pump fuel will like less total but the same or more initial timing. that has to do with the way cylinder pressure builds as the mixture burns and the angles of the rod and crank. As your static ratio is a little low (again, IMO) you never would be near the detonation threshold nor would you have hot spots leading to pinging. So there wouldnt be much of a loss with more timing. There's extra "room" in the chamber and loss of pressure that regardless of what you do it would run. That's more than likely why it was built just that way. More room for error without damage. If you've never had the engine itself dyno'd you might want to save up and have it done. You might be surprised at where the power peaks really occur. I think the torque peak's lower than your convertor stall.
 
I have not had the engine dynoed, but I did get a Chasis dyno run in at the Souther nationals 2 years ago. Also, below is a pic of the est. from Dyno2003.

Reckon the +5 degrees could cause blowby?

Screen 01.jpg


Screen 02.jpg
 
piston rings cause blowby and those look like really low numbers for a stroker??
 
74Burntorange said:
piston rings cause blowby and those look like really low numbers for a stroker??
Click to expand...
Yeah, this is before tuning, a worn out convertor and with the excessive timing. With tuning and the new convertor on slicks it did get into the 12 teens.

When we took it apart, the rings looked good, but the cylinder walls were smooth. Still not sure why I had so much blowby, unless the rings were collapsing, or just never seated well. I am now hypothesizing that the excessive timing may have been partly to blame.
 
I don't think the timing had anything to do with your ring seal/cylinder surface. If it wasn't pinging, its nothing to worry about. The pistons get hurt from too much timing, I've seen a few engines with cracked and blown out ring lands from really bad pinging. It seems the cylinder surface was just not prepped right, and or bad clearances.
 
ah that would do it, i have oil coming out of my filter but I have no baffles
 
5° will not destroy an engine unless it's boosted and on the verge of detonation. It's simply not that big of a deal. I know you've already had it assembled... what did the bores look like? Ring wear is affected by a few things... The two biggest are wall finish and cleanliness when assembling. You ned to wipe the bores until the cloth comes off totally clean. Any particles left stuck in the surface features will damage the rings and negatively affect ring seating and eventual sealing. You also need to realize that the wall's surface looks different when the finish is correct. It might feel smooth if it's wrong, but it will look different. I'm attaching one so you can see the almost polished finish of a correct bore finish for a moly coated top ring. If you see the cross hatch prominently and it's not shiney, it's way too rough and the rings will seal, but not very well, and not for very long. I'm thinking if it's got that much blowby either the original finish was wrong or the walls were dirty when it was assembled. Overall the engine makes some steam. But I believe you were leaving a lot on the table and it had nothing to do with 5° of ignition timing. What was the trap speed of the 12.1 runs?

006.JPG
 
did you ever check and make sure the cam was degreed correctly again..I know since you did the degreeing your self
 
Was looking at old posts and if the damper in this post 0,s at 5* atdc wouldnt he always be setting the timing retarded instead of advanced or am I missing something?
 
daredevil said:
Was looking at old posts and if the damper in this post 0,s at 5* atdc wouldnt he always be setting the timing retarded instead of advanced or am I missing something?
Click to expand...

I think your looking at it backwards Pete. With the balancer the way it is it showing 5 degrees retarded he would be advancing the timing 5 degrees to make up for it.
 
daredevil said:
Was looking at old posts and if the damper in this post 0,s at 5* atdc wouldnt he always be setting the timing retarded instead of advanced or am I missing something?
Click to expand...

Think of 34* as 2.125 inches from 0 on the dampener/timing cover. If 0 is actually 5* retarded then he`s been setting his timing closer to 2.75" from actual zero (-5*) or closer to 39*btdc. It is a bit confusing.
 
I have the same balancer must be pro/street and mine was off by the same not only that my pully was out of alignment also.
 
so I take it you have found tdc going clockwise and then counter clock wise thensplitting the diff, right?

cause there be some dwell time at tdc.

most are off, my cover is marked too.
 
1wild&crazyguy said:
so I take it you have found tdc going clockwise and then counter clock wise thensplitting the diff, right?

cause there be some dwell time at tdc.
most are off, my cover is marked too.
Click to expand...

Yes, that is the correct way to do it. As you said, there is too much dwell at TDC till the crank starts moving the piston down again. To be fair, it was a 60's engine with the bolt on timing tab. Almost all are off in my experience, most not worth worrying about. Unless you are as picky as I am.

You should start a thread for engine builders/machinists/anyone about mistakes or things way out of tolerance you have found or seen. I still remember a couple of doozies.
 
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