Firing Orders -> Bearing wear.... A Discussion.

[OVERKILL]

I've been thinking (a dangerous thing at times).

The traditional V8 firing order for both the SBC and SBF (things are a bit more convoluted with Dodge, so I'll omit them for now) was:

Ford Y-Block: 1-5-4-8-6-3-7-2
Ford 302/289: 1-5-4-2-6-3-7-8
Chevrolet/GM: 1-8-4-3-6-5-7-2
Ford "HO"/351: 1-3-7-2-6-5-4-8
Chevrolet LS1: 1-8-7-2-6-5-4-3

For reference.

As far as Ford goes, the change in firing order on the Windsor engine to the HO/351 version was done when they increased the power output. This has been Ford's "defacto" firing order since on all V8 engines. The reason for the change was that, from my research, it was shown to provide much more even loading of the crankshaft, reducing bearing wear.

Some may disagree, but I believe GM's own research agrees with this, and when the LSx engines were developed, they adopted the same cylinder firing order.

The Lopo Windsor, when it wore rod bearings, would wear the first couple cylinders. The 302HO does not have this problem, nor does the 351W. Keep in mind, it takes substantial mileage for this to be observed.

They have the same oil pump......

Where am I going with this?

Well, when I was thinking about the BMW S62 bearing wear "issue", it started me thinking about the firing order.... So I looked it up:

BMW numbers their cylinders in the same way as Ford does. And it appears they use the same firing order as the old Y-Block, which is much closer to that of the lopo Windsor and SBC, than it is to the 351/302HO and GM LSx engines.

The bearing "wear" with the S62 seems to happen regardless of oil choice. While most people who have done the "bearing swap" have been running the TWS 10w60, that is likely due to most people using that oil in the first place. How the sample of those who've replaced their bearings compares to the number of those who have not (the highest mileage forum member at the M5board doesn't use TWS, but I think that's a red herring) I'm not sure.

However, being a Mustang forum member forever and a day, and having owned a number of 302HO's, rod bearing wear is never an issue of discussion.... EVER. Unless somebody has an engine that has had a bad life.... And then upon tear down, the wear is on ALL the bearings, not just the rod bearings.

So I guess, and I am just thinking out loud here..... If the bearing wear on some S62's is related to BMW's (poor?) choice of firing orders compared to Ford and now, more recently, GM. We all know the Modulars routinely rack up ridiculous mileage. I've never heard of rod bearing issues with them, even in Cobra/Shelby/GT500 service either.

Thoughts?

 

[Charlie1935]

Some one screwed up on the flat head Ford.

 

[OVERKILL]

Originally Posted By: Charlie1935
Some one screwed up on the flat head Ford.


Noticed that! Go MSD! LMAO!

 

[dparm]

My 4.2L 40V V8 has the same firing order as the above BMW, for what it's worth.

 

[spasm3]

when i rebuilt a ford 302, i used a 351 camshaft so i could change the firing order. looked like the bearings were worn more on that end where 1 and then 5 fired.

 

[OVERKILL]

Originally Posted By: spasm3
when i rebuilt a ford 302, i used a 351 camshaft so i could change the firing order. looked like the bearings were worn more on that end where 1 and then 5 fired.


Exactly. 1/5 are the ones that wear with the "old"/lopo firing order. The HO/351 firing order "fixes" this.

 

[mechanicx]

I don't think the different firing order necessarily causes more bearing wear. The sbc is not know to wear bearings. It may be possible that some V8s due to crankshaft and block design or torsional damping could show more problems with the other firing order, but I'm not sure about that. I think the reasons for using one firing order or the other are for reasons other than just bearing wear.

 

[OVERKILL]

Originally Posted By: mechanicx
I don't think the different firing order necessarily causes more bearing wear. The sbc is not know to wear bearings. It may be possible that some V8s due to crankshaft and block design or torsional damping could show more problems with the other firing order, but I'm not sure about that. I think the reasons for using one firing order or the other are for reasons other than just bearing wear.


The SBF isn't "known" for it either. But a high miler will always have more wear on 1/5 with the "lopo" firing order, whilst an HO will have perfectly even wear, and less of it with the same mileage (generally).

I assume you've had a few SBC's apart, do you notice that 1/2 are more worn than the rest?

 

[Shannow]

Firing order can and does affect wear rates. They explained it at uni, and I'm pretty vague on it, but the beefier the bottom end, the less effect that it has.

 

[mechanicx]

I had never noticed a wear pattern on sbc main and rod bearing, but I wasn't really thinking about it and that doesn't mean none exists. Maybe someone else knows a pattern. On a lot of 90 degree V8 cranks some cylinders can rob another cylinder for air (but your Bimmer has an IR intake)so may see differences in pressure pulse vs other cylinders, that and I assumed some bearing journals may receive oil better (that might not be true though) and I assumed outside cylinders and front cylinder potential ran a tad cooler, plus slight differences in machining clearances. Another factor might be whether the engine is internally or externally balanced. So bottom line is I didn't expect to see a pattern because of the variables.

That said I do believe the 2 or 3 different firing orders that were commonly used on V8s can and do have some effect on crank load, but I think it depends on the engine whether it causes more bearing wear. I don't think the sbc firing order caused more wear on 1/2, but it might. On some V8s it could very well be a problem.

 

[SteveSRT8]

I have had more than a few high mileage sbc's, and never noticed this issue.

But logically it does make sense. I will run this past my BIL who is a third gen machinist, he may have seen something relevant.

 

[mechtech2]

Something must be flexing.
The oil is not induced in to the bearing by the firing order, and the loading is the same.
Could be crank or block flex.

 

[OVERKILL]

Originally Posted By: mechtech2
Something must be flexing.
The oil is not induced in to the bearing by the firing order, and the loading is the same.
Could be crank or block flex.


Explain please.

Obviously the oil distribution to the crankshaft in no way corresponds to the firing order. However, each cylinder, when it fires, induces a load on the crankshaft. It is the timing of these induced loads that is determined by the firing order. If you have a whole pile of them going off on one end of the crank, that end is going to experience more load.

 

[mechanicx]

AS I said earlier, I agree that the firing order has some effect on crank loading, but whether it actually has any effect on bearing wear is dependent on a particular engine's crank and block stiffness and resistance to harmonics. That's probably what mechtech is getting at.

Quote:
In the realm of OE production engines, the altered firing order is said to increase engine smoothness. In fact, when we questioned Gen III valvetrain engineer Steve Pass, he said the firing order was dictated by the crank guy. That was Bill Compton, who had this to say via e-mail: "Since the G3 engine was a clean-slate project, each group looked at things that they could change to optimize the performance of the small-block. Although we did not have an issue with crankshaft loading on the older V-8s, there was room for improvement in the area of distributing the peak firing loads among the five crankshaft journals. Analysis showed that main 4 had peak loads significantly higher than main 2. By changing the firing order, the peak loading on main 4 was reduced and the peak loading on main 2 went up. Overall, the loading through the mains was much better balanced. By improving the load balance across the crank, we created a better balanced oil film interface across the crank. The valvetrain group simply changed the cam lobe timing to work with the new crank firing order."

Read more: http://www.hotrod.com/techfaq/113_0701_lunati_cams/viewall.html#ixzz1XfcIPec7


According to that the old firing order didn't cause a loading issue for the sbc and the changed firing order moved the peak load from main 4 to main 2 but overall load was more even. This doesn't really address the question of whether changing the fire order resulted in actually lowering bearing wear or not. Perhaps it would on an aluminum block LS but make no difference on the SBC, but that's pure conjecture. However, the LS firing order "improving the load balance across the crank and better balanced oil film interface across the crank" suggest the pontential is there.


You have to wonder why GM and so many other manufactures used the 18436572 firing order. I'm betting they knew about the pros and cons of the different firing orders. It's just not clear to me why they didn't use the "LS" firing order when it seems to have no real downside. What was the common, old firing order giving them if anything keeping in mind dual plane carburetion, distributors and often but not always siamesed cylinder ports?

 

[Shannow]

When in University, I was living on the 7th floor overlooking a fairly decent road with a set of stoplights about 200 feet down the road.

Although a Holden guy, I certainly liked the bloke who designed the SBC firing order a lot more than the bloke who did the Holdens (1-2-7-8-4-5-6-3), which sound really "flat" when accelerating.

 

[mechanicx]

The "1-8-4-3-6-5-7-2" firing order does have a meaner sound to it. Who knows, back in the 50's when most of those V8 were designed it may have come down to the engineers liked the engine sound better lol. Besides most of those classic V8 bottom ends were over-engineered for the power levels and whatever harmonics advantage swapping 8-7 and 3-2 had was probably inconsequential.

I wonder if anything enlightening is in these papers:
http://papers.sae.org/550263
http://papers.sae.org/970915

 

[JHZR2]

My answer?

BMW makes INLINE engines. You strayed, now you may pay...

Go M42 and N55!

j/k, well kind of. I dont have a technical basis, but I think your observation is very good and may well have some basis. Problem is, what can you do? Somehow reprogram the ECU to fire differently? Install new cams and timing setup to enable this?

 

[OVERKILL]

Originally Posted By: mechanicx
AS I said earlier, I agree that the firing order has some effect on crank loading, but whether it actually has any effect on bearing wear is dependent on a particular engine's crank and block stiffness and resistance to harmonics. That's probably what mechtech is getting at.

Quote:
In the realm of OE production engines, the altered firing order is said to increase engine smoothness. In fact, when we questioned Gen III valvetrain engineer Steve Pass, he said the firing order was dictated by the crank guy. That was Bill Compton, who had this to say via e-mail: "Since the G3 engine was a clean-slate project, each group looked at things that they could change to optimize the performance of the small-block. Although we did not have an issue with crankshaft loading on the older V-8s, there was room for improvement in the area of distributing the peak firing loads among the five crankshaft journals. Analysis showed that main 4 had peak loads significantly higher than main 2. By changing the firing order, the peak loading on main 4 was reduced and the peak loading on main 2 went up. Overall, the loading through the mains was much better balanced. By improving the load balance across the crank, we created a better balanced oil film interface across the crank. The valvetrain group simply changed the cam lobe timing to work with the new crank firing order."

Read more: http://www.hotrod.com/techfaq/113_0701_lunati_cams/viewall.html#ixzz1XfcIPec7


According to that the old firing order didn't cause a loading issue for the sbc and the changed firing order moved the peak load from main 4 to main 2 but overall load was more even. This doesn't really address the question of whether changing the fire order resulted in actually lowering bearing wear or not. Perhaps it would on an aluminum block LS but make no difference on the SBC, but that's pure conjecture. However, the LS firing order "improving the load balance across the crank and better balanced oil film interface across the crank" suggest the pontential is there.


You have to wonder why GM and so many other manufactures used the 18436572 firing order. I'm betting they knew about the pros and cons of the different firing orders. It's just not clear to me why they didn't use the "LS" firing order when it seems to have no real downside. What was the common, old firing order giving them if anything keeping in mind dual plane carburetion, distributors and often but not always siamesed cylinder ports?


What you've quoted supports why Ford switched to that firing order back in the 60's on the 351's, and why only the 302HO got it, and not its "lopo" brother. I think on engines with lower power output, it is, as you've surmised, inconsequential. However, turn-up the wick and the "better" firing order results in less wear.

The LS1 made more power stock than any of its predecessors. Similarly, the 302HO, though by no means anything close to the power output to the LS1, made a lot more power than its "lopo" sibling, and made that power higher in the RPM range.

If we look at the modern examples like the Modular and the LSx family, there is a common theme in terms of both stupidly long-term durability as well as very good power output. Something the families they replaced didn't do. If we look back at the power output of engines through the 70's and 80's and compare them to what their displacement-similar cousins are making today.... Well there is no comparison. And these new engines last far longer than their predecessors ever did. I've never seen a 1.2 million Km Windsor. But I've seen a 4.6L with that mileage. How many miles do SteveSRT8's 6.0L GM's have on them now? And in what kind of service?

Perhaps I'm extrapolating a little too much on what the guy quoted stated. But at the same time, I think he has very much reinforced the logic behind Ford's decision so many years ago.

 

[BobFout]

Wow a V4, haven't seen those in a while.

 

[ms21043]

Some observations:

According to MSD's chart, flat head ford and modern Hemi fire 3 cylinders on one bank consecutively?...oops.

GM, AMC and Chrysler V8's except LS and nail head have the same firing order as Ford 289, 302, FE, 429, 460.

GM LS has the same firing order as Ford 351, 400, 5.0 EFI and Mod.