Home » Public Forums » GMCnet » Piston rod stretch in the 455 (Another mode of bearing failure?)
| Piston rod stretch in the 455 [message #279727] |
Fri, 12 June 2015 12:08  |
cbryan
Messages: 451
Registered: May 2012
Location: Ennis, Texas
Karma: 3
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After all the talk about lugging the engines being destructive to the well-being of the powerplant, resultant focus on the pistons, etc. I am still wondering about one more thing.
Note that Dick Paterson rebuilds his 455s with loose rod bearing clearances and with high volume oil pumps.
I gathered from some other sources that weak rods will go oval, egg shaped at the big end due not to compression pressures, not to detonation, but from rpm. The rod has to make sure the piston stops at TDC, obviously. It is stressed in the elongation direction there, especially at the exhaust stroke. If the rod isn't very strong at the sides of the big end, it might be possible for the sides to move toward the journal enough to cause metal to metal contact, heating, and knock, knock, knock. So, Paterson checks for ovality, and then makes sure there is a lot of area for the rod to collapse inwards before untoward noises spring forth. The Oldsmobile rods are supposedly not too strong. I do believe there are aftermarket rods that are much stronger. If we are to wind out our engines, are we not 'asking for it' with stock rods?
I write this not because I have conviction either way, only to broach another factor that may bear on the "normal" failure mode of the 455. It is rod knock. Presumably, if the oil pressure alone was the culprit, there would be an equal number of main bearing failures, and I am not positive about most of the failures being those of rod bearings. There is the problem of contaminated oil galleries, oil coolers in radiators with debris from the last fiasco still in them, oil pumps damaged and not checked, all can contribute to catastrophic failure. Lighter pistons might help with stock rods if a hedge of bets is called for.
Here's to a meaningful dialogue. Is this effect where the term "hot rod" comes from?
Carey
Carey from Ennis, Texas
78 Royale, 500 Cadillac, Rance Baxter EFI.
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| Re: [GMCnet] Piston rod stretch in the 455 [message #279732 is a reply to message #279727] |
Fri, 12 June 2015 13:12  |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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The big ends go out of round in Olds 455 and to some degree in 350 and 403
Olds as well. Testing in real world use kind of points towards high piston
loading at lower rpm's (lugging the engine) rather than stretching from
high engine rpm's. (Extension loads) Microscopic analysis shows
compression loads rather than extension loads in the grain structure. Our
coaches see a heck of a lot of low speed /high piston loading use, and
almost no high rpm's. That is what I see when I measure big ends of
connecting rods out of round. Couple that with machine shops that don't
re-cut the tang notches after resizing the rods and you have a recipe for
spun rod bearings and improper loading on the inserts. What's the fix? Rev
Em up. Regear the final drives. Shift them down, let the lower gears in the
transmission take some load off the tops of the rods. Take your foot out of
it on heavy climbs. Set your ignition timing correctly. Use gasoline
appropriate for your compression ratio.
Jim Hupy
Salem, Or.
78 GMC ROYALE 403
On Jun 12, 2015 10:08 AM, "Carey Bryan" wrote:
> After all the talk about lugging the engines being destructive to the
> well-being of the powerplant, resultant focus on the pistons, etc. I am
> still
> wondering about one more thing.
>
> Note that Dick Paterson rebuilds his 455s with loose rod bearing
> clearances and with high volume oil pumps.
>
> I gathered from some other sources that weak rods will go oval, egg shaped
> at the big end due not to compression pressures, not to detonation, but
> from rpm. The rod has to make sure the piston stops at TDC, obviously.
> It is stressed in the elongation direction there, especially at the exhaust
> stroke. If the rod isn't very strong at the sides of the big end, it
> might be possible for the sides to move toward the journal enough to cause
> metal
> to metal contact, heating, and knock, knock, knock. So, Paterson checks
> for ovality, and then makes sure there is a lot of area for the rod to
> collapse inwards before untoward noises spring forth. The Oldsmobile rods
> are supposedly not too strong. I do believe there are aftermarket rods
> that are much stronger. If we are to wind out our engines, are we not
> 'asking for it' with stock rods?
>
> I write this not because I have conviction either way, only to broach
> another factor that may bear on the "normal" failure mode of the 455. It
> is rod
> knock. Presumably, if the oil pressure alone was the culprit, there would
> be an equal number of main bearing failures, and I am not positive about
> most of the failures being those of rod bearings. There is the problem of
> contaminated oil galleries, oil coolers in radiators with debris from the
> last fiasco still in them, oil pumps damaged and not checked, all can
> contribute to catastrophic failure. Lighter pistons might help with stock
> rods
> if a hedge of bets is called for.
>
> Here's to a meaningful dialogue. Is this effect where the term "hot rod"
> comes from?
>
> Carey
> --
> Carey from Ennis, Texas
> 78 Royale, 500 Cadillac, Rance Baxter EFI.
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
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| Re: Piston rod stretch in the 455 [message #279745 is a reply to message #279727] |
Fri, 12 June 2015 16:51 |
Gary Mau
Messages: 152
Registered: February 2004
Location: Davenport, Iowa
Karma: 0
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Jim,
When you said " Use gasoline appropriate for your compression ratio" are you saying not to use premium in a stock 455? The only way we can get non ethanol here in Iowa is to buy premium, 91 octane.
Gary Mau
Former 76 Royale owner
Davenport, IA
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| Re: [GMCnet] Piston rod stretch in the 455 [message #279750 is a reply to message #279745] |
Fri, 12 June 2015 17:16 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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No, the problem comes from too low an octane rating, not too high. Some
coaches have had extensive modifications to the heads, larger bore sizes,
block milling, pistons changed, etc. All to increase the compression ratio.
As a very general rule of thumb, 8.5 - 1 C.R. should require a minimum 85
octane fuel. 10.0 - 1 should take 100 octane. These figures are not true in
every case. Too many variables to list. I won't even talk about blended
fuels here. Besides drinking, the one good thing that alcohol is okay as,
is an anti-knock compound. But I don't want to stray off topic too far.
Jim Hupy
Salem, Oregon
On Jun 12, 2015 2:51 PM, "Gary Mau" wrote:
> Jim,
>
> When you said " Use gasoline appropriate for your compression ratio"
> are you saying not to use premium in a stock 455? The only way we can get
> non
> ethanol here in Iowa is to buy premium, 91 octane.
> --
> Gary Mau
> 76 Royale
> Davenport, IA
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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| Re: [GMCnet] Piston rod stretch in the 455 [message #279776 is a reply to message #279727] |
Sat, 13 June 2015 08:48 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Carey,
What was the source of the information regarding Dick Paterson's engines?
Regards,
Rob M.
The Pedantic Mechanic
-----Original Message-----
From: Carey Bryan
After all the talk about lugging the engines being destructive to the well-being of the powerplant, resultant focus on the pistons,
etc. I am still wondering about one more thing.
Note that Dick Paterson rebuilds his 455s with loose rod bearing clearances and with high volume oil pumps.
I gathered from some other sources that weak rods will go oval, egg shaped at the big end due not to compression pressures, not to
detonation, but from rpm. The rod has to make sure the piston stops at TDC, obviously. It is stressed in the elongation direction
there, especially at the exhaust stroke. If the rod isn't very strong at the sides of the big end, it might be possible for the
sides to move toward the journal enough to cause metal to metal contact, heating, and knock, knock, knock. So, Paterson checks for
ovality, and then makes sure there is a lot of area for the rod to collapse inwards before untoward noises spring forth. The
Oldsmobile rods are supposedly not too strong. I do believe there are aftermarket rods that are much stronger. If we are to wind
out our engines, are we not 'asking for it' with stock rods?
I write this not because I have conviction either way, only to broach another factor that may bear on the "normal" failure mode of
the 455. It is rod knock. Presumably, if the oil pressure alone was the culprit, there would be an equal number of main bearing
failures, and I am not positive about most of the failures being those of rod bearings. There is the problem of contaminated oil
galleries, oil coolers in radiators with debris from the last fiasco still in them, oil pumps damaged and not checked, all can
contribute to catastrophic failure. Lighter pistons might help with stock rods if a hedge of bets is called for.
Here's to a meaningful dialogue. Is this effect where the term "hot rod" comes from?
Carey
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] Piston rod stretch in the 455 [message #279784 is a reply to message #279776] |
Sat, 13 June 2015 10:03 |
cbryan
Messages: 451
Registered: May 2012
Location: Ennis, Texas
Karma: 3
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Senior Member |
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Rob,
Here's a quote indicating Dick's preferences, though second hand:
"Thanks, that's good input. I'll probably do similar things, and although
>> 35 psi isn't too low, I like you, would probably be a little happier with it
>> a little higher. That 10 psi per 1,000 rpm rule of thumb has been around
>> at least as long as I have, and though I probably won't see 5,000 rpm, when
>> I go to 3.70 gears, being at 4,000 or a bit more is probably going to
>> happen at least sometimes. So, sounds like high volume oil pump it is!
>> Part of
>> Dick P's philosophy is to go on the loose side with clearances to get a
>> lot of oil flow to take heat away from places where it isn't good.
>> --
>> Craig Lechowicz
>> '77 Kingsley, Waterford, MI"
Dick does have some kind of magic that mere mortals rebuilding Olds engines can at times seem to get wrong.
Here's a quote from this forum, not Dick Paterson:
"Here's the thing with the Olds 455. These torgue monsters have over 13 feet
of bearing surface which is huge which means alot of flow is needed. The
big journsls and narrow bearing surface means oil has to get in and get
because of heat just like paterson says. That being said, the flow is more
important than pressure alone.
As far as clearances go, no less than .0035 on both rod and mains. Some of
my friends that build Olds, are hsrd and fast on no less than .0040. With
those clearances you'll see some pressure drop but you'll have good oil
flow through the the bearings reducing heat and the risk of those bearings
grabbing each other and spinning.
A mileage saver and wear reducer is to use forged pistons or cast with the
low tension rings 1.5mm rings and 3mm oil rings.
Sincerely?
Jim Ernst
77 palm Beach
77 Kingsley
Columbus, Ne"
Best,
Carey
Carey from Ennis, Texas
78 Royale, 500 Cadillac, Rance Baxter EFI.
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| Re: Piston rod stretch in the 455 [message #279789 is a reply to message #279727] |
Sat, 13 June 2015 10:48 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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As to the first paragraph and why more often the rod bearings than mains. Oil flows to the mains first but then has to travel through the crank throws to get to the rods. As RPM increases so does the throwing of oil at the rods. Not sure if the correct term would be centrifugal or centripetal force. So correct me. This is great news for the cly walls and pistons for cooling but the forces pull oil out of the throws and big rod ends to where the cushion layer is lost. Just like your washing machine extracts water during spin but this is at about 4 x the RPM compared to the washer where 1000 RPM would be a fast one. So call that the 'high RPM fail mode'. At the other end of the RPM range high load and low oil pump RPM, the rods are again last in line to get a drink and cly pressure loads can exceed the film layer thickness. Call that 'lugging failure mode".
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: [GMCnet] Piston rod stretch in the 455 [message #279805 is a reply to message #279768] |
Sat, 13 June 2015 14:23 |
BobDunahugh
Messages: 2465
Registered: October 2010
Location: Cedar Rapids, IA
Karma: 11
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Senior Member |
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John. You are correct about the cooling affect of oil spray. But if the oil pressure is at 35 PSI a 1000 RPM or at 4000 RPM. The clearance between the crank, and bearing remains the same. Thus the orifice so to speak remains the same. The same applies to a HV pump. You came increase the amount of oil to the bearing. But the clearance stays constant. Thus no extra oil can get thrue the clearance between the crank, and the bearing. Thus no extra oil to cool. Plus I have never heard of, or seen that there was a problem with over heating of piston's in the 403 or 455. To pump more of anything takes energy. That just makes more heat. Simple laws of physics. So to me. I see no reason to fix a problem that doesn't exist to begin with.Bob Dunahugh78 Royale
The stock GM rod is up to the task in our application. Don't lug the engine. Never let it ping from pre ignition. Have the rods re sized. And never have the bearing clearance over .001 Rod bearing clearance starts out at .0003 of an inch from GM. GM says that .003 is at the end of usable. The usable limit for me with the engines I build is .0007 tops. The rods that I use in my Yenko's are stock GM. Run them to 8,000 RPM's. Never had one fail in the last 25 years. But I do spend a lot of time making them perfect for the task.
Gary asked about using premium gas in a stock 455. Our stock compression 403, and 455 can use 89 octane gas if you set the timing, and carb up correctly. It's a simple rule. Use the lowest octane you can and not have it ping. I put 89 octane with ethanol in my 403. Have a 3:70 final drive. Pull up to 21,000 gross weight. I pulled my wife's lift van that comes in at 5,000 lbs plus for 3700 miles. And got 10.122 MPG. Higher octane gas is for engines that are of a higher compression desigh.
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| Re: Piston rod stretch in the 455 [message #279812 is a reply to message #279727] |
Sat, 13 June 2015 16:37 |
Chris Tyler
Messages: 458
Registered: September 2013
Location: Odessa FL
Karma: 7
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Bob, I think you'd have to agree all GM rods arent the same. Your Chevy rods in your Yenko were a better design even before you massaged them I would bet.
Olds rods arent the best, but at least they arent the cast junkers that Pontiac used. Ask me how I know.
Rod stretch is more of a problem with RPM, and more with free reving without a load from what I have seen
Id have to agree that lugging is a bigger problem for our application. Piston speed [discussed elsewhere today] is higher with a longer stroke, and energy being a function of mass x velocity it goes up exponentially, but not a problem with our RPM range. True, there is more friction, but via more leverage and a longer burn time, more torque.
When were talking about lugging, its really about preignition or detonation that spikes the cyl pressure or worse, creates too much pressure while still compressing BTDC. Plays hell with rod bearings and pistons, especially cast
Once the bearing goes, the rod follows.
Guys that worked for GM I knew swore Olds engines were more precisely assembled than other GM marks. I would bet their tolerances were on the mark, and most rod failures are either high milage or after a shoddy rebuild on the rod. The clearance is critical, and the bearing is held in place by proper crush. I dont know if olds uses tabs, but I have seen a lot of poorly resized rods that were not recut correctly and failed
Hard to find really good machine work anymore.
76 Glenbrook
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| Re: [GMCnet] Piston rod stretch in the 455 [message #279821 is a reply to message #279784] |
Sat, 13 June 2015 19:18 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Carey,
Thanks, I suspected the information was second hand and not directly from Dick.
I have an engine that I bought from a guy up in Canada that was removed from his GMC that burned to the ground. The engine was
supplied to the owner by Dick.
As I disassembled that engine I was overwhelmed by the phenomenal attention to detail I saw. Suffice it to say every time I removed
another component I found little things that would enhance increase power and longevity.
Dick and I have had many discussions about that engine during which he explained the "little things" and why he does them. They made
total sense to me.
It should be noted that Dick has supplied lots of Olds engines to GMCers with hi flow oil pumps in them and they perform very well
and are reliable. Furthermore when they do have a problem he takes responsibility and fixes the problem.
Regards,
Rob M.
The Pedantic Mechanic
-----Original Message-----
From: Carey Bryan
Rob,
Here's a quote indicating Dick's preferences, though second hand:
"Thanks, that's good input. I'll probably do similar things, and although
>> 35 psi isn't too low, I like you, would probably be a little happier with it
>> a little higher. That 10 psi per 1,000 rpm rule of thumb has been around
>> at least as long as I have, and though I probably won't see 5,000 rpm, when
>> I go to 3.70 gears, being at 4,000 or a bit more is probably going to
>> happen at least sometimes. So, sounds like high volume oil pump it is!
>> Part of Dick P's philosophy is to go on the loose side with clearances to get a
>> lot of oil flow to take heat away from places where it isn't good.
>> --
>> Craig Lechowicz
>> '77 Kingsley, Waterford, MI"
Dick does have some kind of magic that mere mortals rebuilding Olds engines can at times seem to get wrong.
Here's a quote from this forum, not Dick Paterson:
"Here's the thing with the Olds 455. These torgue monsters have over 13 feet
of bearing surface which is huge which means alot of flow is needed. The
big journsls and narrow bearing surface means oil has to get in and get
because of heat just like paterson says. That being said, the flow is more
important than pressure alone.
As far as clearances go, no less than .0035 on both rod and mains. Some of
my friends that build Olds, are hsrd and fast on no less than .0040. With
those clearances you'll see some pressure drop but you'll have good oil
flow through the the bearings reducing heat and the risk of those bearings
grabbing each other and spinning.
A mileage saver and wear reducer is to use forged pistons or cast with the
low tension rings 1.5mm rings and 3mm oil rings.
Sincerely?
Jim Ernst
Best,
Carey
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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