Checking/adjusting engine timing

[s2cmpugh]

Good day everyone. Changed the timing belt myself last weekend (car runs good, revs freely, no weird noises), but I want to double check the timing. I was going to rent a timing light from Autozone, but wanted to get some help on exactly how to set up the light, adjust the timing, and a general process for it.

Thanks,
Cris P.

[deevergote]

The timing light is to check ignition timing. It really has nothing to do with the timing belt.
The light should come with illustrated instructions.

[batever]

Good day everyone. Changed the timing belt myself last weekend (car runs good, revs freely, no weird noises), but I want to double check the timing. I was going to rent a timing light from Autozone, but wanted to get some help on exactly how to set up the light, adjust the timing, and a general process for it.

Thanks,
Cris P.

To check the base ignition timing:

Jumper the service connector on the right side firewall under the glove compartment. It is a small blue connector with two openings: put a bent paper clip or staple in both holes to connect them electrically. This tells the ECU not to modify the timing (according to rpm) beyond the base timing (Base timing is set up by how you have set up the camshaft pulley in relation to the crankshaft pulley during your timing belt change. Since the distributor runs directly off the camshaft, the camshaft setting directly affects the distributor timing).

Now hook up the timing light with the inductive clamp over spark plug #1 wire, and power it from the car's battery with the two leads supplied.

Now start the car and let it warm up till it drops to warm idle, around 700 rpms. Technically this shouldn't matter but that's what they say to do.

Now flash the timing light onto the flywheel throught the hole in the tranny bellhousing and see which mark the light lights up and how that mark lines up with the pointers. If the red (+15) mark shows up right in the center of the timing pointer, then the timing is right on. If it show up "below" the pointer, then the timing is retarded. If it shows up "above" the pointer then the timing is advanced.

Get the timing as close as possible to +15 degrees by turning the car off, loosening the 3 12mm mounting bolts on the distributor, and slightly rotating the distributor (by infinitesimal amounts) and see how that affects the ignition timing and gets the +15 mark right between the pointers. Secure the distributor each time before starting the car up again.

ignition timing is based off the valve timing in our cars, which you set with the timing belt. generally you can be either +2 or -2 beyond +15 degrees before top dead center and the car will perform pretty well (those two marks on either side of the red +15 mark are the marks for +2 and -2 degrees from 15 degrees BTDC). But dead on at +15 degrees is a good place to be.

don't forget to remove the jumper from the service connector when you're done or the car won't be able to modify the base timing according to the rpms of the engine (the ECU will slightly advance the timing as the rpms climb in order to make the combustion event happen as close as possible to the ideal time (right at/slightly before piston top dead center) vis a vis piston movement at all engine speeds).

[johnl]

The timing light is to check ignition timing. It really has nothing to do with the timing belt.

The distributor is driven from the end of the camshaft, and the camshaft is driven by the timing belt. So, if the old timing belt were slightly stretched then fitting a new unstretched belt would result in both the valve timing and the ignition timing being slightly advanced compared to the timings with the old belt.

However, I've heard that these belts are reinforced with kevlar cords, which is highly resistant to stretching. If so then I doubt there is likely to be any significant difference in belt length between an old and new belt.

The only way to know would be to check the timing before and after changing the belt. If there was any significant stretching of the old belt, then it should show up as the ignition timing being slightly retarded, assuming that the timing was set perfectly when that belt was new...

[deevergote]

If the timing belt is stretched or improperly fitted, checking the ignition timing is a BAD way to check it. The proper way to check the physical timing if the engine is with the markers on the cam gear and crank pulley.

[batever]

The distributor is driven from the end of the camshaft, and the camshaft is driven by the timing belt. So, if the old timing belt were slightly stretched then fitting a new unstretched belt would result in both the valve timing and the ignition timing being slightly advanced compared to the timings with the old belt.

However, I've heard that these belts are reinforced with kevlar cords, which is highly resistant to stretching. If so then I doubt there is likely to be any significant difference in belt length between an old and new belt.

The only way to know would be to check the timing before and after changing the belt. If there was any significant stretching of the old belt, then it should show up as the ignition timing being slightly retarded, assuming that the timing was set perfectly when that belt was new...

Regarding either improper fitting or belt stretch:

Shooting from the hip, if the belt or pulley is off by one tooth measured at the crankshaft end, it will put the valve timing off by ((1/number of teeth on the crankshaft timing pulley)*360/2) degrees while putting the ignition timing off by (1/number of teeth on the crankshaft pulley* 360 degrees).

If the belt (or pulleys) are off by one tooth at the camshaft end it will put the valve timing off by a *lot* more, I believe it will be 2* (1/number of teeth on the camshaft pulley)*360 degrees while the ignition timing will be off by a lesser (tiny) amount, I believe (((1/number of teeth on the camshaft)*360)/2) degrees.

I have never counted the number of teeth on the respective pulleys so that's why I can't give the exact answer in degrees.

However, my ignition timing became something like an estimated 8 or 10 degrees retarded when I did my timing belt job and ended up with the crankshaft timing pulley off by one tooth, so something on the order of 8 degrees per tooth for that is probably right.

Anecdotally, with regard to the lack of stretching of the belts under use, other members, who, unlike me, work on cars for a living have responded to one of my posts to say that they have never seen an Accord timing issue due to a stretched belt. Kevlar could be the reason.

[batever]

If the timing belt is stretched or improperly fitted, checking the ignition timing is a BAD way to check it. The proper way to check the physical timing if the engine is with the markers on the cam gear and crank pulley.

It's not a conclusive way but it's a lot faster as an initial diagnostic than pulling the timing covers off if they are already on the car again. If the ignition timing is off by more than 5 degrees or so you might have cause to suspect improper timing belt installation, assuming the ignition timing was close to on target before the timing belt job was done.

[deevergote]

The ignition timing will be off as long as the distributor was removed and the position was not marked. If it is 5 degrees off, that could simply be due to the way the distributor was replaced.

If you use a timing light properly and you can't find the timing marks on the flywheel... THEN it would suggest that the timing belt was off in some way.

[batever]

If you use a timing light properly and you can't find the timing marks on the flywheel... THEN it would suggest that the timing belt was off in some way.

That's exactly what happened to me. No ignition timing marks were in sight when using the timing gun after the t.b. change (1st attempt). I guess it was off by a lot more than 5 degrees.

I wish I knew the number of teeth on the pulleys so I could figure out how much each tooth of displacement of each pulley affects the valve and ignition timing. However I'm not going to pull the car apart just to count them!

[deevergote]

That's what junkyards are for Or a good picture found online.

If you can't get the timing marks in sight by moving the distributor as far as it can go in either direction, there is a problem. OR you have a replacement flywheel without markings. My XTD POS flywheels don't have markings (I just pulled one out and installed another one...)

[s2cmpugh]

I think I might be OK, but let me tell you guys how I did the TB change.

1. I made sure everything was at TDC, but looking at the various reference marks.
2. I made a mark that connected a valley on the old TB thru to the camshaft pulley. I then made a second mark on the crank pulley and onto the old TB. This allows me to know the EXACT distance of the belt
3. I then counted the valleys b/t the marks on the old belt, and transferred those markes onto the new belt so the distance was the same.
4. I installed the new belt lining up the marks I made on the new belt w/ the marks on the camshaft pulley and crank pulley.
5. After installing the new TB and BB we rotated everything once and it lined up perfectly.

This helps to make sure I didn't get anything off when I put the new belt on.

[batever]

I think I might be OK, but let me tell you guys how I did the TB change.

1. I made sure everything was at TDC, but looking at the various reference marks.
2. I made a mark that connected a valley on the old TB thru to the camshaft pulley. I then made a second mark on the crank pulley and onto the old TB. This allows me to know the EXACT distance of the belt
3. I then counted the valleys b/t the marks on the old belt, and transferred those markes onto the new belt so the distance was the same.
4. I installed the new belt lining up the marks I made on the new belt w/ the marks on the camshaft pulley and crank pulley.
5. After installing the new TB and BB we rotated everything once and it lined up perfectly.

This helps to make sure I didn't get anything off when I put the new belt on.

If you did all that you're golden, especially if the car still runs good after the job.

[s2cmpugh]

If you did all that you're golden, especially if the car still runs good after the job.

Awesome! The car runs real good. Only issue I have is a cold start problem, but I'm going to replace the plugs, fuel filter, rotor button, dist. cap, and get some new wires. If the car sits for a couple days (fully cold start) sometimes I have to crank it twice, but it does start.

Should I check the timing anyway to be sure?

Thanks,
Cris P.

[batever]

Awesome! The car runs real good. Only issue I have is a cold start problem, but I'm going to replace the plugs, fuel filter, rotor button, dist. cap, and get some new wires. If the car sits for a couple days (fully cold start) sometimes I have to crank it twice, but it does start.

Should I check the timing anyway to be sure?

Thanks,
Cris P.

Well it can't hurt to check the ignition timing, particularly if you have never checked it, but it certainly doesn't sound like it's a problem that needs addressing or anything in your case. Your ignition timing is probably pretty "on" if the car is running well and has a nice smooth powerband.

I would put it on the "B list" for things to do when you get around to it and do other stuff first, particularly if you've owned the car for a while and never had any real problems with for example low mpg. If you had a timing light it's no problem to check whatsoever later.

The cold start problem is not going to be related to the ignition timing; your approach of checking plugs, wires, battery, and dist cap is the way to go with that.

[johnl]

If the timing belt is stretched or improperly fitted, checking the ignition timing is a BAD way to check it. The proper way to check the physical timing if the engine is with the markers on the cam gear and crank pulley.

Yes of course, I was assuming correct instalation of both the old and new belts. Given that, if the new belt results in the ignition timing becoming advanced over what it was with the old belt, it's a reasonably safe bet that the old belt must have been significantly stretched. It's an academic argument though considering that the timing belts seem fairly immune to stretching...