Why 2650rpm max?

[patracy]

I don't know if anyone is still reading this post, but since I'm a Newbee and have only gotten so far in my reading I'm really behind the eight ball here.
As a ASE certified Master Mechanic for over 30 yrs I've seen a lot of engines blown apart. The main reason I've seen pistons ventilate blocks is due to
lack of oil. Most all diesels and heavy gas engines ( IHC etc.) have large surface areas on the rod bearings and when these engines start spinning high
they really need the lube to keep the clearances up. Remember, the bearing really rides on a film of oil not the bearing itself. When you spin high with a low volume
oil pump and low pressure like the multifuels (30 psi ) the system cannot keep up with the oil lose, this creates heat, which creates friction , which creates added stress to the rod bolts,
which ends up with rods flying through block ! That is why all racers use high pressure, high volume oil systems costing lots of money !
I've built up International engines that can really rev , but you need high tensile strength bolts, balanced rotating mass, and really good lube systems. Not to mention
high pressure valve springs and lifters and cams !

Pressure (PSI) is an indication of resistance, not flow.

Have you had a multifuel open before? There's two oil filters, huge pick ups (two), also they run 30psi at idle. Hot and at speed is typically 60psi. Also there's oil squirters for the pistons. I'd have to say these are not low volume setups.

The rod bolts tend to be a common theme to this discussion. There's a number of reasons they're discussed. But I personally would side more towards the fact that these engines (in their original diesel only config in tractors) had a much lower operating range. They were then asked to increase that range, increase the CR substantially, and then you also have to consider that most of the engines were "rebuilt". Often, the rebuilders had only picked up a wrench recently.

I'll see if I can find my scale, but I've got a set of take out rods and pistons from a MF. I'd be willing to bet there's a good bit of difference between them.

This is absolutely my opinion, but I believe a LDT/LDS could be rebuilt to balanced and blueprinted spec. A better set of rod bolts installed. And you could subject them to 3K rpm all day long. I do not however think I'd replace the valve springs, as the actual camshafts have been known to shear at the sprockets. (I would however check and shim all the springs to ensure even valve seat pressures)

 

[m-35tom]

original max rpm was 2200 when used in a tractor (white) increasing the rpm is always a case of diminishing returns higher rpm always = lower reliability shorter engine life. on top of that there is no good reason to ever run more than 2500 rpm.

 

[Jeepsinker]

What do people do when they rebuild these engines? Reuse the bolts again after they have been reused who knows how many times already? Is there even a reliable source for n.o.s rod bolts for these? If not there surely must be another engine that uses compatible rod bolts.

 

[JasonS]

PThere's a number of reasons they're discussed. But I personally would side more towards the fact that these engines (in their original diesel only config in tractors) had a much lower operating range. They were then asked to increase that range, increase the CR substantially, and then you also have to consider that most of the engines were "rebuilt". Often, the rebuilders had only picked up a wrench recently.

Just to be clear, the multifuel was derived from the TD6427 industrial/ transportation engine NOT a farm tractor engine. The white/ oliver tractors were a later adaption of the multifuel (with lower compression ratio, Roosamaster pump, etc). The multifuel was a SIGNIFICANT redesign of the TD6427. Maybe "derived" is a stretch as it really shares few aspects of the TD6427 engine. The TD6427 had smaller bearings, one cylinder head, oil pump driven off of the cam via a right angle drive, Lanova combustion chamber, bypass oil filters, block didn't extend below the crank center-line, etc. It is really more derived from the larger R series but with even larger bearings. The original rpm rating of the TD6427 was 2400 rpm. By the way, Continental had electric grid heaters for cold weather starting.

 

[rustystud]

Patracy, I said VOLUME and PRESSURE. I've seen and built many engines including the MAN engines people keep talking about, and in most all cases when there is major failure like a rod through the block it can be traced back to oil lose. Right now I work for a major transit agency with over 1400 buses. Recently we went through a series of Cat engines ( C9 ) that would lose there rods through the block. They had use replace the rods and pistons and bolts and you name it. It finally came out that it was a major engine flaw, especially in how oil was distributed. As far as the multifuel having 2 filters and 30psi at idle , that still does not mean it has sufficient VOLUME of oil to compensate for lose at high speed. The International Harvester engines where extremely dependable. I know, I worked at the dealership for years until IHC went bankrupt.
I also had over 10 IHC trucks . That was until the wife got fed up and made me get rid of most of them . At one time I decided I would find out why you can't rev a 392 or 345 IHC . I spent over $2000.00 on machining and parts and finally got an engine that would rev reliably over 4000 rpm. The most important find I found was that the block was stepped drilled for the oil passages. The front main bearing especially had only an 1/8" opening, though the main passage started at over 3/4". The reason they did this is because the passage was right at the edge of the block. I was able to drill this out to 5/16" being very careful to not exit the block thus increasing oil VOLUME to this bearing which also fed the rod. This did not increase PRESSURE . Later I installed a high PRESSUE and high VOLUME pump. At idle the pressure was 45psi and at speed it would reach over 85psi. With over twice the VOLUME of oil pumped. The gears in the pump where the same size only twice as tall . Meaning more oil was pumping out.
As a side note, most MAN diesels used over here are the PANCAKE style block, just like VW's and the Chevy Corvairs.

 

[JasonS]

Patracy, I said VOLUME and PRESSURE. I've seen and built many engines including the MAN engines people keep talking about, and in most all cases when there is major failure like a rod through the block it can be traced back to oil lose. Right now I work for a major transit agency with over 1400 buses. Recently we went through a series of Cat engines ( C9 ) that would lose there rods through the block. They had use replace the rods and pistons and bolts and you name it. It finally came out that it was a major engine flaw, especially in how oil was distributed. As far as the multifuel having 2 filters and 30psi at idle , that still does not mean it has sufficient VOLUME of oil to compensate for lose at high speed. The International Harvester engines where extremely dependable. I know, I worked at the dealership for years until IHC went bankrupt.
I also had over 10 IHC trucks . That was until the wife got fed up and made me get rid of most of them . At one time I decided I would find out why you can't rev a 392 or 345 IHC . I spent over $2000.00 on machining and parts and finally got an engine that would rev reliably over 4000 rpm. The most important find I found was that the block was stepped drilled for the oil passages. The front main bearing especially had only an 1/8" opening, though the main passage started at over 3/4". The reason they did this is because the passage was right at the edge of the block. I was able to drill this out to 5/16" being very careful to not exit the block thus increasing oil VOLUME to this bearing which also fed the rod. This did not increase PRESSURE . Later I installed a high PRESSUE and high VOLUME pump. At idle the pressure was 45psi and at speed it would reach over 85psi. With over twice the VOLUME of oil pumped. The gears in the pump where the same size only twice as tall . Meaning more oil was pumping out.
As a side note, most MAN diesels used over here are the PANCAKE style block, just like VW's and the Chevy Corvairs.

Won't keep an overstressed rod bolt from failing at extended high speed operation.

 

[JasonS]

Reliability reasons aside, the efficiency of the multi drops off significantly at high rpms.

 

[rustystud]

JasonS, I didn't go into all the details of the machining work done to the IHC engine. One of the mods was to use the Mopar Direct Connection 440cid HiPo rod bolts. This intailed drilling out the rod ends, fitting
the bolts, then machining the rod ends to the correct size.
Another thing that needs mentioning is that the bearing width on these old engines are much wider then new style diesel engines. Take the new CAT or Cummins engines. There rod bearings are almost the same width as a big block chevy 454 or a Chrysler 440. They are much larger in diameter, but the width is almost the same. Of course this is only possible due to the increase in the strength of steels used today in making the new rods. Surface area equals friction. So if we make a new crank out of one of the many new alloys ( forged of course). Install new H beam style rods, with new Hypertuenic Pistons , and a new
High flow-High pressure oil pump with a new style variable rate turbo, I believe we could make the multifuel really fly ! Of course we would also have to change the injection pump and injectors Just a few
simple mods that's all

 

[JasonS]

When rods have failed, it has been catastrophic with no apparent damage to the crank other than contact directly after breakage. If there were insufficient oiling, I would have expected there to be damage all the way around the crank.

Bearings need to have enough surface area (width and diameter) to support the loads. They also need sufficient diameter to achieve the surface speed to form a hydrodynamic wedge. It is this wedge which separates the crank and bearing; not the oil pressure. I don't have time to dig out my Clevite book but CAT and Cummins diesel engines have always had much larger bearings than 454s.

 

[gimpyrobb]

JasonS, I didn't go into all the details of the machining work done to the IHC engine. One of the mods was to use the Mopar Direct Connection 440cid HiPo rod bolts. This intailed drilling out the rod ends, fitting
the bolts, then machining the rod ends to the correct size.
Another thing that needs mentioning is that the bearing width on these old engines are much wider then new style diesel engines. Take the new CAT or Cummins engines. There rod bearings are almost the same width as a big block chevy 454 or a Chrysler 440. They are much larger in diameter, but the width is almost the same. Of course this is only possible due to the increase in the strength of steels used today in making the new rods. Surface area equals friction. So if we make a new crank out of one of the many new alloys ( forged of course). Install new H beam style rods, with new Hypertuenic Pistons , and a new
High flow-High pressure oil pump with a new style variable rate turbo, I believe we could make the multifuel really fly ! Of course we would also have to change the injection pump and injectors Just a few
simple mods that's all

We have had numerous guys come on here talking about "just need to"...
None of them follow through. if the motors fail from not enough oil, my motor would have had holes in it long ago. As I was driving down the interstate, I lost an oil drain plug from my oilpan. After another member brought me some oil and another turbo(losing the oil melted the original turbo) I filled up on oil, started the truck and finished my trip. That trip was another 30min to my destination and then 3hrs home.

This is the same motor that was in my truck when I rolled it while off-roading. I'm sure these motors fail due to the hard life they have led while in service and maybe some of the rebuild places didn't quite pay enough attention to what they were doing. Just a glimpse into what mine has survived and its still kicking azz and taking names.

 

[Jeepsinker]

There has to be another engine that uses compatible rod bolts. Anyone that rebuilds it diesels often watching this that can chime in? Seems to me that just balancing the engine and getting new rod bolts would be a big step up in reliability. They don't necessarily have to be performance rod bolts, just good new ones.

 

[JasonS]

There has to be another engine that uses compatible rod bolts. Anyone that rebuilds it diesels often watching this that can chime in? Seems to me that just balancing the engine and getting new rod bolts would be a big step up in reliability. They don't necessarily have to be performance rod bolts, just good new ones.

There have been two types of rod bolts used in the multis: 6 point and 12 point. It appears that the 12 point is in later build engines. It also appears that the failures have been predominately (or even confined to) the 6 point bolts. You can determine which bolt you have by looking through the rear oil drain plug. You can get new 12 point bolts from Hercules. I have posted several sources in an earlier thread.

 

[Tow4]

Just remember you need to resize the rod ends when you change the rod bolts. You can't just pull the pan and change the bolts.

 

[JasonS]

Just remember you need to resize the rod ends when you change the rod bolts. You can't just pull the pan and change the bolts.[/QUOTE

Why would you have to resize? Unlike a small block chevy with bolts/ nuts and and the bolts having interference fit in the rods; the multi's rod is threaded with bolts that fit loose in the cap and only provide a clamping force.

 

[Jeepsinker]

There have been two types of rod bolts used in the multis: 6 point and 12 point. It appears that the 12 point is in later build engines. It also appears that the failures have been predominately (or even confined to) the 6 point bolts. You can determine which bolt you have by looking through the rear oil drain plug. You can get new 12 point bolts from Hercules. I have posted several sources in an earlier thread.

Excellent, I've read a lot of threads on this topic and never seen you post that up. Must have been after I read through them. Really good news to hear though.

 

[rustystud]

JasonS, look at the new Cat C9 and the Cummins ISL & ISC engines. To gimpyrobb, how high of RPM was your engine running at ? At my Tech school to demonstrate the lack of oil on engine, we took a Chrysler 318
dumped all the oil and ran it with a brick on the gas peddle, full throttle. It lasted quite a long time. In fact we stopped it and drained all the coolant then restarted it and again full throttle. The engine never blew up, it just slowed down and then stopped . After tear down we checked the engine and of course the bearings where toast as expected. Now your probably saying "see you made my point ! " but what the tear down
showed was the clearances due to worn out bearings already. There was enough slop in the bearings to allow for thermal expansion, so the rods never seized up. Would this engine have lasted long in normal
driving ? No, that's why it was donated to the school due to rod knock. Eventually something would have gone boom.
JasonS said it himself when he talked about the wedge of oil. I said it before and I'll say it again, the rods and crank don't ride on the bearings, they ride on a film of oil. And when a engine is over reved it will fling out the oil faster then it is replaced by a stock style pump unable to keep up with the oil lose.
As far as you OLDER and WISER guys on this site knowing everything there is about these trucks, you should remember there are plenty of guys , like me who served in the military (Marines 6yrs) who drove these trucks as part of there daily jobs, worked in the motor pool, repaired them, drove them for days with seized clutches (try shifting with out a clutch) because the Captain said so. Slepted under them at night.
Got then unstuck on beaches with the tide coming in (the Sargeant Major was drunk and decided it would be a good idea to drive into the ocean) Who maybe know a thing or two about these rigs.
Of course I'm probably wrong, you guys know better, my bad.

 

[rustystud]

JasonS, when I went with the HiPo rod bolts I had to resize the rod ends due to the expansion from the drilling out to the larger size. It's not much, but remember that the clearances are in the thousandths of an inch.

 

[MarkM]

Interesting thread. It all comes down to the rotating mass of the assembly at higher RPMS and the imbalance, Extra heat soaking cycles, Tension on the rod bolts, Inherent tolerances of older designed engines and so on. The manufacturers goal is to produce an engine that will perform satisfactorily and reliably to a given workload and environmental conditions at the lowest possible overall cost. Sure you can do modifications so that the engine will be slightly more reliable at a higher max RPM but the gain will have diminishing returns in engine life longevity and premature parts fatigue and failure. Is it really all that necessary to get to the coffee shop 5 min faster?

Mark

 

[gimpyrobb]

Rusty, I was cruising about 2500rpms. When I heard the turbo burn up, I immediately shut the motor down. It has been a year or two and I have driven her a lot since then. I'm not saying I know it all, just what my experiance has been. The oil pressure has not dropped and there is no knocks, so I will truck on. I have had a lot of things break on my truck while out driving, but nothing makes me think I am driving a "time bomb" waiting to blow up on me. I am quite fond of the multifuels.

 

[JasonS]

JasonS, when I went with the HiPo rod bolts I had to resize the rod ends due to the expansion from the drilling out to the larger size. It's not much, but remember that the clearances are in the thousandths of an inch.

Apples and oranges comparison. One uses a bolt pressed into the rod with a nut on the cap and the other is just a bolt on the cap.