Tech time mag probe

[quickster]

Hey folks. I can't get the probe to fit in the tube over the damper. A 5/16 drill bit doesn't help any. Anything else I can use that I'm not thinking about? And also should I set the unit to 9.5 before timing- I seen some posts that folks left the unit at 20 degrees to time, but you don't want 9.5 at idle. You want 9.5 at 2000rpm. This is for my 87 6.9. Anyway, I can't do squat till i get the thing in the hole. Thanks.

 

[CharlesG]

Try a larger drill bit or a small file. Some people have filed the probe to get it to fit.
The tube for the probe is 20 degrees off of TDC, so you need to set your meter to account for the offset.

 

[ComatoseLlama]

I had to use my bench grinder to take down the probe to get it to fit. It also seems to be tricky to get it to work correctly, mine won’t work and I believe @TNBrett is having trouble getting his to work.

An alternative is a 7” timing tape on the harmonic balancer and using a normal timing light along with the tachtime inducer to measure the timing.

Here’s the thread on timing tape

 

[quickster]

I have an adjustable timing light with a timing unit that has a line clamp, but it's so erratic that I figured if I get a proper timing unit I wouldn't have to second guess the readings anymore. I'm going to try and find a 8mm drill bit cause that's the size of the probe. I know if I try and file the probe down , Murphy's law will come into full effect.

 

[Big Bart]

That is the issue with some of the Tech Time's on Ebay, some were made for other engines. If you want to use the probe method some have had to drill out the hole or grind down the tip (Could cause it to break if not careful.) to make it fit.

Also as I recall there is a warning not to hook up the timing probe until the unit is powered up. Double check in your manual, I have not heard of folks having a issue, but often folks say the probes later do not work. I wonder if due to the fact they are fragile, or many just made the mistake of hooking up prior to powering up.

When using the timing light method, the light will be erratic but I find generally at 2,000 rpm the light seems to even out and only miss a blink occasionally but does not seem to bounce the timing all over. Just goes on and off, the timing mark seems to mostly be in the same place. So do not be concerned if your light evens out at 2000 rpm. Now if your timing is all over the place at 2000 rpm, then your pulse sensor/piezo is not reading right, or your light does not like the Tech Time. (Move it, do not place on turns in the pipe, and sand the paint off the lines before putting it on.) Many have had to try a different timing light to get it to work with that metal pulse bar. I use a Snap On and I have pretty good luck.

Yes you can set the timing to 9.5 degrees BTDC as many like it there. Ford said 8.5 degrees BTDC, you choice. Per many a member who did, do not leave the IP loose when starting and try to adjust. Shut off, adjust, retighten, and then re-check.

Keep in mind you need to do the 20 degree offset if you use the probe on the crank dampner. (Not the timing light.) That is because the hole you are supposed to use is not at TDC. It's 20 degrees ATDC. There is a smaller hole at TDC, but that is not the hole you should use. If you use the timing light, you do not use an offset, rather you set your timing light to the desired timing (9.5 or 8.5) till your dampner timing mark is at TDC. That is because there is no 8.5 or 9.5 marks on the timing tab coming off the gear case. So the only known mark to align up with is TDC. So the advance on the light causes the flash and what you see to come 8.5 or 9.5 degrees late. Thus flashing on TDC but the engine is at say 8.5 BTDC.

 

[TNBrett]

Mine has worked fine for me. I just had to file my probe down a bit to fit. I believe they may be meant for an 8mm tube, and ours are 5/16”. With variations in tolerances it may or may not work in your engine, but it’s only a few thousandths that it needs to be taken down. It’s a job for a file and some emery cloth in my book, I would avoid a grinder.

 

[quickster]

I went out and picked up a 21/64 drill bit with a hex end and drilled out the hole. Had to remove some belts and alt bracket, but got it done. Going to try the timing unit out tomorrow. Just so you know, that tube will spin on the mounting plate, so you need a pair of vise grips to hold it from spinning. I used a 1/4 in drive ratchet and socket to "drill" the hole out. A couple turns in, then back it out. Took forever but what are you gonna to do. And lots of oil.

 

[gandalf]

This is all interesting. Are there perhaps slightly different models of this timing unit? Mine is a Model 3300-S. As I recall the EBay ad said it was for a Hummer, but would work on other engines also. Initially I had trouble getting the probe to fit into the hole. I used a 5/16 drill bit to clean the hole, holding it and rotating it by hand only. I had no problem with the probe following that. I did have to hunt for a good ground, ending up using a bolt on the engine. The cords were long enough that I could set the unit on the hood and read it from inside the truck, using the throttle as normal to control engine speed. The timing unit and my tachometer disagreed on the RPM by as much as 200 RPM.

 

[Big Bart]

They only make one size of magnetic pick up probe. So perhaps the hole in the idi corodes/rusts over time. Thus the need to drill them out. Perhaps they were intended for another engine like for a Hummer or Duramax and you have to make the idi hole bigger.

 

[TNBrett]

Make sure the hole is clean. Use a 5/16 drill bit with your fingers, gun cleaning bore brush, etc. But, 8mm is .315”, and 5/16 is .3125”. It doesn’t take much to take .0025” inches off with a file, and you can do it standing up at your workbench as opposed to laying under your truck. Plus, I’d rather risk damaging the magnetic probe rather than the timing indicator on your engine.

 

[quickster]

The 5/16 fit good, actually a little sloppy. But the probe is 8mm. I bored it out rather than mess up the probe. The timing unit is most likely intended for a certain mfg. Or more like the probe is intended for a different truck.

 

[Scotty4]

The military national stock number (NSN) on the front is for timing the Humvees.

 

[quickster]

So 21/64 works perfect. Ok, so now that it all works, the 6.9 is set at1400 rpm iirc, correct? At@1400 my timing is at 8.7 to 9. You have to hold the rpm's dead nuts to get an accurate reading. I'm impressed. So I timed it pretty damn close with my other timing unit, which will be going up for sale shortly.

 

[Big Bart]

Quickster,

Not so fast, it’s 8.5-9.5 btdc at 2,000 rpm. Not 1,400rpm.

You will need to recheck and perhaps retime.

Let us know how it goes.

 

[quickster]

7.3 is timed at 2000. All I ever read on here was 1400 for the 6.9. Unless all that I read here was wrong, or mixing it up with something else. Was just double checking. Took it up a big hill near me and no smoke. Sounds and feels good.