DIY LTCC or similar system for LT1s

[vilefly]

Oh, I forgot. Did you intend to scan in your optical wheel? I think it would be a great idea, since it would allow us to copy it and check it for trueness with a CAD program. I am currently trying to draft one up using emachineshop.com 's free cad program. I intend to make another mountable wheel that would let one generate an LS crank/cam signals directly with no conversion. The great part is that the cad program lets you do estimates of the cost of a production run. It would be awesome to just drop in a wheel, and use any engine management system you like.

I have been known to scan in carburetor gaskets at actual size, and reproduce that which could no longer be bought. If I was feeling fancy, I would even load up the gasket paper directly in the printer. Works like a charm. Great also for making TBI to carb adapters from scratch, too. I had to remember to print out with the "actual size" option selected.

[spfautsch]

I did that today, but I wouldn't recommend using either of the wheels I have as a pattern.

Extremely disappointed with the remanned distributor base. I had high hopes of it being worthwhile b/c it was expensive for only a base, was described as a delco-remy and the rebuilder riveted their name to it so I assumed they were proud of their work. They shouldn't be - it was a remmaned aftermarket piece of garbage that I'm probably going to try to return. The trigger wheel had C4105-11 etched on it. The bearing was tight, but sounded like an egg beater when spun like the hub had been pressed in without supporting the center race. The optical sensor was marked J520.

To add insult to injury, when I put it on to test the low res signal was extremely inconsistent. The controller would lose track of whether it was on or off because it was giving multiple edge triggers. I seriously doubt it would have ran had I installed this in-car and tried starting it.

Out of curiosity I tried the old optical sensor that was in mine when I bought the car (that was setting a DTC for loss of hi res). I observed the same type of erratic behavior on the hi-res output.

The only positive that came of it is that the trigger wheel gave slightly better results. I put it in my distributor base because I didn't like the way my "good" AIP sensor fit in the aftermarket base. Timing was still skewed but the difference between cyl 6 and 8 was consistently 3 degrees instead of 4 with the 3001277 wheel. Putting both wheels on the hub and aligning them carefully I was able to observe differences in the size of the low res cutouts, albeit with a magnifying glass. Most were towards the indexed side of the slot, but #8 was on the TDC side.

I did quite a bit of experimenting with the mechanics of the opti today (mines a gen 2 vented). I found that removing the o-rings from the shaft made it obvious there's some slop between the cam dowel and the hub. Enough that I could consistently make the high res signal change state by wiggling the rotor back and forth. The o-rings damp this slop somewhat, until they get hard. I didn't have a chance to dig out my original cam and check the dowel diameter (think it's supposed to be .250"). But if the aftermarket cam dowel is within tolerance this would illustrate how big of a design flaw this is, and why most of the newer engines have the degree wheels integral to the crank casting.

I also removed the hub on my old opti to try and find sizes on the bearing. The grease seals on it were marked 6903-RS but it's obviously a custom-order bearing - the outer race has an integral shoulder for the retaining ring. Without this shoulder it would be dimensionally identical to a 6903 bearing (17x30x7) but didn't bother measuring the diameter of the shoulder.

Without more test subjects to confirm or disprove whether the timing skew I'm observing is common, I'm not terribly happy with the state of things so I'm back to looking for a source for an original degree wheel to test. That, or I dump another 5 bennys and a quarter on a dynaspark.

[vilefly]

How about this flanged bearing?
http://www.vxb.com/F6903ZZ-Flanged-S...-p/f6903zz.htm
F6903ZZ-2.jpg

If not, use the designation "NR" after the bearing number to do a search. 6903 NR, and similar, 6903 zznr, ss6903 nr, etc. I have to tend to the "squab", and keep her out of the bathroom before she develops a killer bacterial weapon in there.

[spfautsch]

I'll have to pull the hub back out and will post pics and dimensions. The shoulder is in the middle of the bearing with steps down to the nominal 33mm race size in front and back, so that probably wouldn't work just from eyeballing it. This is another area where GM really screwed the pooch on design - all in the name of saving a quarter of an inch.

The hub is a relatively loose press fit to the shaft and I believe even OE used threadlocker to secure it once aligned to TDC. It's fairly easy to remove by holding the hub with something and tapping the shaft out with a punch - no vise or pullers required. Most of the rebuilders drill a 3/32 hole for a roll pin at the mating line before disassembly so they don't have to re-index the hub. I don't want to attempt to remove the hub from the bearing without a replacement bearing, so that will be at the very bottom of my bucket list.

I'm not feeling like messing around in the garage any more tonight - just finished the 44th oil change (x 10,000 mile interval) and tire rotation on my daily driver, removed the trigger wheel to return the junk distributor base for a refund, and washed the sooty smelling oil off my hands. Going to spend some time relaxing and entertaining my daughter's dog that she swore up and down she was going to take care of. The animal would fetch the tennis ball from 6am to midnight if there was someone willing to throw the damned thing that long.

The results I had with the other trigger wheel seem to show the a similar pattern of timing skew, trending towards +3 degrees between cyls 1 and 8 and zero around cyl 6. The only explanation I can think of for this other than a junk trigger wheel is that my cam gear is slightly elliptical. Without others reproducing this test on different engines I don't really feel alarmed enough to warrant pulling the timing cover and possibly creating a new oil leak. For all we know at this point, a brand new OE timing set might produce more erratic results. And though we're geographically diverse beyond the pale of vision, I don't see a line forming of LT-1 owners wanting to yank their water pumps to attach a degree wheel and find true mechanical TDC to verify. Ultimately my intentions were to upgrade to an electric water pump so I can run a standard double roller timing set, so maybe that will be my excuse to pull the engine next winter.

[kur4o]

Why don`t you hit the local scrapeyard. There might be some cheap not working units. Anyway you only want the stock gm wheel.
New opti is almost impossible to find. Even GM sells only reman units now.

If we follow common sense you`re timing gear should be a little too tight. Since you hit alot of *5s at idle and stretched chain gives *7s.
Eleptical wheel will produce too many vibration when spun at high rpm.
You can compare chain link counts with crank sprocket tooth counts. If they have 2:1 ratio it is possible that half the chain is busted.

[Terminal_Crazy]

Why don`t you hit the local scrapeyard. There might be some cheap not working units. Anyway you only want the stock gm wheel.
New opti is almost impossible to find. Even GM sells only reman units now.

If we follow common sense you`re timing gear should be a little too tight. Since you hit alot of *5s at idle and stretched chain gives *7s.
Eleptical wheel will produce too many vibration when spun at high rpm.
You can compare chain link counts with crank sprocket tooth counts. If they have 2:1 ratio it is possible that half the chain is busted.

I have a stock 95 opti I can scan if you want when I get back home.

The gears have something like 15 and 30 teeth to give a 2:1 ratio but the chain is longer and the links should walk around so they don’t line up regularly.
Mitch

[spfautsch]

Why don`t you hit the local scrapeyard. There might be some cheap not working units. Anyway you only want the stock gm wheel.

The thought crossed my mind. Generally I go to <big auction site> when I'm looking for scrapyard parts since most yards list stuff there and it saves me the agony of using the telephone and a bunch of driving. I'm not seeing any salvaged optis there. Just one MSD that in the description says it was setting a CMP code so probably needs a new sensor and the MSDs use a proprietary sensor.

But in addition to wanting the correct wheel I'd like a new bearing, and I'm not hopeful of finding a source for one.

If we follow common sense you`re timing gear should be a little too tight. Since you hit alot of *5s at idle and stretched chain gives *7s.
Eleptical wheel will produce too many vibration when spun at high rpm.

If the timing gear wasn't perfectly circular or bore where the cam seats in the gear isn't perfectly centered that would cause the chain to be tighter for half a revolution.

Thinking about this, I've almost worked up the courage to pull the timing cover and see what I find. Maybe I'll put a double roller chain in temporarily and re-test timing. If the cloyes set I put in last year is egg shaped it would really burn me because if memory serves that was a very expensive set.

I have a stock 95 opti I can scan if you want when I get back home.

vilefly might appreciate it.

[spfautsch]

Found a double roller billet timing set (w/o water pump drive) for a very reasonable price so it's on the way.

If it improves or eliminates the timing skew I guess I'll take that last step off the cliff and buy an electric water pump.

Will try to post pics and measurements of opti bearing and base tonight. From extensive reading I'm not feeling very confident an alternative will be possible. I'd really like to remove the hub from the remanned delphi unit to see if there are any part #s visible on it. But I'd also like to be able to return it as it isn't worth what I paid just to gain a better quality trigger wheel.

BTW vilefly the metal shielded bearing type you posted a pic of would be a problem for vented optis because they need to hold vacuum. The vent system might suck the grease out of that one not to mention letting unmetered air into the intake.