Timing chain differences

[MeanLemons]

I was looking at timing chain kits on rockauto and eBay.  Noticed that there’s difference in various year ranges.

 

I'm wondering what’s the difference? 

 

If i put a newer block, for an example, in a renix. Does that mean I need to use renix timing sprockets & chain?

[Rockfrog]

From what I've found so far, the Renix timing set is advanced 4 degrees more that the later HO timing set.
Next weekend, I'll be swapping the timing set out of my old Renix block (was replaced and only used 3 months) into the 97 TJ motor I currently have.
What I've noticed between the old motor and the new motor is the 97 want to Rev high before making any real power. Which seem to support the newer timing being 4 degrees retarded.
From all I've read the Renix set should simply swap in up to late 99 when the newer cam retainer was introduced.

I'll let you know how it works out.

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[HOrnbrod]

8 hours ago, Rockfrog said:

From what I've found so far, the Renix timing set is advanced 4 degrees more that the later HO timing set.

 

First I've heard of that. Not saying it's not true, just haven't read it before. I'm on the strokers forum a lot and some those guys would be all over that....

[Rockfrog]

Yeah, there's not a lot of info out there on the differences. But from what I've found so far the timing (at the timing gears) was retarded by 4 degrees when the HO was introduced.
If it does ring true, it opens up a 4 degrees advance option by using the Renix set on up to a 99 engine.
Like I said, I should be swapping the old (new) renix set onto the 97 motor this weekend so I should have an update by Monday.

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[HOrnbrod]

6 minutes ago, Rockfrog said:

Yeah, there's not a lot of info out there on the differences. But from what I've found so far the timing (at the timing gears) was retarded by 4 degrees when the HO was introduced.
If it does ring true, it opens up a 4 degrees advance option by using the Renix set on up to a 99 engine.
Like I said, I should be swapping the old (new) renix set onto the 97 motor this weekend so I should have an update by Monday.

 

  Very interested.

[Eagle]

The problem is, without comparative dynomometer runs on the same engine and same camshaft with both chains ... how are you going to know? It's going to run. I think you'll have to have a very sensitive "seat of the pants dyno" to pick up on the difference, and if you're dropping a different engine into your truck, any perceived difference could be due to the cam timing, or to other factors.

 

The factory did make some changes but, of course, the parts manual doesn't tell us what the differences are, only that there are different part numbers.

 

87-93 . . . . Chain . . . . 3300 2977

. . . . . . . . . .Sprocket . 3300 2978

 

94-99 . . . . Chain . . . . 5302 0444

. . . . . . . . . .Sprocket . 5302 0445

 

2000 . . . . Chain . . . . 5302 0444

. . . . . . . . . .Sprocket . 5301 0400

 

2001 . . . . Chain . . . . 5302 0444

. . . . . . . . . .Sprocket . 53010 557AA

[HOrnbrod]

19 minutes ago, Eagle said:

The problem is, without comparative dynomometer runs on the same engine and same camshaft with both chains ... how are you going to know?

 

True, not exact science here, but if you throw a timing light on the 97 HO engine w. the new Renix timing set installed, read it, and it's higher than ~12* BTDC (stock HO timing), you'll know it did something...

[Jeep Driver]

I've posted on this before

Ignition timing and valve timing have no relationship to each other, a timing light will tell you nothing.

Particularly when you have no control over ignition timing timing is going to be set to the crank sensor.

The only way you're going to know whether or not you are Advanced or retarded at the valve is use a degree wheel.

I have watched racing engine builders who will factor in advance at the cam knowing that after a couple of runs down the Dragway when they factor in chain stretch they will be straight up when they check the valve timing again.

Some manufacturers will include some advance in the grind when you couple that with advancing at the gear you could be 4 to 6° advance the only way you will know is to either know what the manufacturer has ground into the cam or by putting a degree wheel on the engine and checking your valve timing.

I suspect that particularly if you were using a single roller chain after 40 or 50,000 miles you'll be straight up at valve timing even with 4° advanced

Advancing the timing at the valve creates power at the lower end retarding the timing creates power at the upper end of your RPM range.

[Rockfrog]

Which seems to coincide with the differences in peak RPM's between the two EFI systems. Renix had a torque peak at 2400rpm whereas HO bumped that up to 4000rpm, then dropping to 3400rpm with the new cam (dual pattern) in 97.

So as the early HO and renix Cams were the same, it seems to lend some credence to a difference in initial cam timing, rumor or not, I'll do it anyway, since I have a new (run for about 12,000kms maybe) set and the 'new' motor (97 TJ) has an old stock set with roughly 150,000kms on it.

 

Curiosity being what it is, what's the worst that could happen ....

 

I know, but can't hurt to try.

 

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[Eagle]

3 hours ago, Jeep Driver said:

I've posted on this before

Ignition timing and valve timing have no relationship to each other, a timing light will tell you nothing.

Particularly when you have no control over ignition timing timing is going to be set to the crank sensor.

 

 

The distributor is driven by the camshaft. Retard the camshaft and you retard the spark. Or, at least, you retard where the distributor rotor is relative to the turrets in the cap. And don't forget that there's a distributor sensor involved as well as a CPS.

[johnj92131]

For what it's worth I have read about the 4 degree different cam timing before to explain different peak torque rpm on Renex vs HO 

[Jeep Driver]

2 hours ago, Eagle said:

 

The distributor is driven by the camshaft. Retard the camshaft and you retard the spark. Or, at least, you retard where the distributor rotor is relative to the turrets in the cap. And don't forget that there's a distributor sensor involved as well as a CPS.

Again they're not related you can turn the distributor on a standard distributor ignition you can turn it to 34 degrees it doesn't really matter

As far as the CPS is concerned the ECU is reading the CPS at the crank which has absolutely nothing to do with cam timing or valve timing the cam only changes the relationship between the cam and the crank that's it everything else Remains the Same

[Eagle]

1 hour ago, Jeep Driver said:

Again they're not related you can turn the distributor on a standard distributor ignition you can turn it to 34 degrees it doesn't really matter

As far as the CPS is concerned the ECU is reading the CPS at the crank which has absolutely nothing to do with cam timing or valve timing the cam only changes the relationship between the cam and the crank that's it everything else Remains the Same

 

Yes, it does matter. At least on the Renix models. That's why the factory issued a TSB on "indexing" the distributor.

[Jeep Driver]

42 minutes ago, Eagle said:

 

Yes, it does matter. At least on the Renix models. That's why the factory issued a TSB on "indexing" the distributor.

OK. 

 

I'm not arguing anymore. 

 

The ECU will not allow you to advance timing. 4 degrees at the crank will only be 2 degrees at the rotor. Since the dist is fixed, as the rotor passes the post, if firing was early on the post before cam advance, it will now be late on the post. ECU will correct timing based on CPS. 

 

 

[Jeep Driver]

 

I watched this over a year ago, IIRC, you won't hear one mention of dist/ignition timing. 

 

Watch if you want to learn about cam timing.

[HOrnbrod]

Rockfrog, when you're done with the  Renix timing set install, please throw a timing light on it and post the results. Thanks.

[Jeep Driver]

Quote

 

Setting Base Timing on the 2.5L TBI Four and the MPI Engines

While the ignition timing is fully controlled by the ECU and ICM systems, the distributor plays a critical role in delivering spark to each cylinder. For the TBI four and later MPI engines with a distributor, the distributor mounts in a fixed position and does nothing more than “distribute” spark to each of the cylinders in the firing order. The ECU computer or PCM knows the piston positions from the crankshaft position sensor (CPS) signal at the flywheel.

Setting fixed timing requires a one-time location of the distributor. On a TBI or MPI Wrangler engine, you cannot adjust spark timing by moving the distributor housing! Timing is a programmed function of the ECU or PCM computer—not the distributor. 2.5L MPI and 4.0L MPI engines locate the rotor in a different position than the TBI distributor depicted in this section. (See ‘Note’ below for MPI timing details.)

 

 

 

http://www.4wdmechanix.com/Tuning-and-Troubleshooting-the-2.5L-Jeep-TBI-Four?r=1

 

 

Maybe you'll believe Moses?

 

 

 

I'm at 4 degrees advanced at the crank, I used a timing  light..........NOTHING changed. 

 

 

 

You guys should study more. 

[HOrnbrod]

1 hour ago, HOrnbrod said:

Rockfrog, when you're done with the  Renix timing set install, please throw a timing light on it and post the results. Thanks.

 

Rockfrog, when you're done with the  Renix timing set install, please throw a timing light on your HO engine and post the results. Thanks.

[Rockfrog]

Fair enough, no way to adjust ignition timing, all good, no argument.
But cam timing in relation to the crank Is Not controlled by the ECU. We are discussing a valve timing difference, the ECU has full and complete control of the ignition event, agreed. But any adjustment at the CPS is still only an electronic adjustment which the ECU can and will adjust for. Granted and agreed. So bear with me while I state my reasoning and understanding here if you would please ...
What I am talking about is changing the actual cam timing and thus the actual valve timing events. Something the ECU has no effect on whatsoever. The ECU/ICM can't adjust valve timing, it can only adjust ignition timing based on the CmPS/CkPS which is still an indexed ignition event. If the valve itself opens 4 degrees sooner (or later) the ECU has no knowledge of it and can't adjust it in any event.
This is what was in rumour/theory was adjusted with the later HO models, the cam timing itself was retarded 4 degrees allegedly. Whether it was for emissions (mimicking some effects of an EGR effect as some have speculated) or some other gloriously lost in the 90's reasoning, the fact remains that the Renix and early HO Cams were the same, and for the most part should (in theory, and from my limited understanding) follow fairly similar (obviously not identical) ignition timing curves given the similarity of the actual base engine .... So I ask then what did they change to create such a massive shift in power peaks? I mean when the TQ peak climbs from 2400rpm to 4000rpm and the overall numbers don't greatly change ... 224 up to 225 ft lbs. If three variations of ignition timing changes produced more and more power output, with no effect on peaks points ... There had to have been a large adjustment made somewhere, no? Which again, leads to a mechanical timing event change (cam to crank relationship).
The only thing the cam sensor and crank sensor really do is dictate where each cylinder is based on number one being at top dead center, I doesn't indicate if the valves are opening at any specific point based on either, that's where the cam lobes and the timing set itself are the sole means of adjustment. The ECU is in a nutshell, just concerned with point A, open injector, make spark, point B, open injector, make spark and so on ... again, all based on rotor position (cam sensor) in relation to cylinder position (crank sensor). The simple fact that the rotor is driven by the cam, does not mean the two events (valve and spark) are controlled or related to each other (other than the fact that they do have to happen within a given window of opportunity for the engine to function).
I'm not trying to pick fights here, I'm merely trying to find an answer to a question that has been asked repeatedly over the years (in my search for an answer I found several other questions on this), and very rarely ever gets answered, and usually with little more than look elsewhere.

Given that 4 degrees of cam timing can/will have a considerable effect of an engine (whether retard or advance from what I've managed to research) .... I aim to find out ... Something ... anything really.

So, what say the more knowledgeable?

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[Rockfrog]

 
Rockfrog, when you're done with the  Renix timing set install, please throw a timing light on your HO engine and post the results. Thanks.

I don't expect to see much change there as the relationship between the crank, the rotor, and the piston won't really change, and the ECM will adjust into spec as it always does.
I'm more expecting to see a basic shift back to the low grunt typical of a Renix, with the usual top end "wheeze out"
Right now, the motor literally runs like my 2000 XJ does, where the power really comes on above 2200rpm and keeps pulling up past 3500rpm (I hate pushing it past there personally). I mean there is some grunt, but not like the original (and quite worn out) motor had, it was a very noticeable difference. The new motor is way more powerful than the old one is by leaps and bounds (well given that it's 10yrs newer and in far better shape internally), but I hate pushing an inline so high, I'm merely hoping to shift the power curve back down lower is all. In no way am I thinking of any huge power gains.
Who knows, there may be no change at all, well, other than those of putting a less stretched timing chain into place. But, like the GM TPS swap I did, and the 97+ MAP swap .... only one way to know for sure. And since I have to do the whole cooling system anyway (rad, thermostat and pump), the front of the engine will laid bare for the taking so why not?

I dunno, I've had stranger ideas ...

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[Eagle]

You'll probably get better fuel economy, too. I recently did a 200 mile road trip in my 2000 XJ 5-speed. I had to keep the speed below 65 MPH due to a tire balance issue -- I got 20.4 MPG.

 

When my '88 XJ 5-speed was a couple of years old, I once got 28 MPG on a trip from Connecticut to Vermont -- with a girlfriend, two kids, and everything that entourage required for a long weekend.