Engine Mount Design Collaboration.

9550 Views 128 Replies 20 Participants Last post by MaxPF, 2 d ago

Dougal

Discussion Starter · May 13, 2021

Hi Guys

I know engine mounts are always a hot topic. Which ones work best, which ones fit best, which ones you can actually source.
I have reached out to Barry Controls: https://novibration.com/ and they're keen to design us a standard fitment to help out with vibration isolation and make all this easy.

But we need some info:
Weights. That should be easy.
Standard mounting configurations that work for most swaps. Particularly fore/aft location on the engine.
Space constraints inside frame rails etc.

I'm also going to forward some Isuzu 4BD1T info that can help too.

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char1355

· #121 · 5 d ago

Engine mounts for the 4bt have always been an issue due to vibration. The 4bt's firing order makes it a vibrating creature. The 6bt is very tame in comparison. You won't find 6bt mounts taming the 4bt. They generally transmit too much vibration to the chassis. Max, that is good info concerning mounting arm length. Those long arms become huge levers which could lead to problems. The 4bt vibration dampening cams are mentioned. They work great but have limitations. Max RPM is 2000. They were mainly on generator applications. There have been several models of those over the years. They aren't road practical and certain ones are horribly expensive. Plus they would need more lower clearance since they use the center sump oil pan. Here's a photo of one of the models 3914763. Retail price is around $5000. Bet that was a popular option. LOL. It's obsolete. No clue how much those bolts cost.

Road use 4bts came with 3 basic engine mounts. One was an angle type like is typically found on gas engines. They worked OK but transmit quite a bit of vibration. The second one was the Lord fluid type mount which replaced the angle type and was vastly superior. The third type was found in later delivery vans which used SAE transmission mounts. Those had a 3 point mounting system with one on each side of the flywheel housing and one up front in the center. Freightliner used this style. About every other type you can think of has been tried over the years. None have been found to be perfect, but some are definitely better than others.

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MaxPF

· #122 · 4 d ago

I don't see any reason why that counter-balance unit couldn't be spun to 2500-2800 RPM. I would feel safe doing so. As you pointed out though, availability and price could be an issue. And it requires a special, deeper oil pan that could cause issued in many, if not most, vehicles.

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char1355

· #123 · 4 d ago

Cummins claims that if those cams in that unit are spun too fast they will explode. They were mainly found on generators that spin at 1800 RPM. Not the same as having them inside an engine where you have more bracing. Many 4 cylinder gas engines have a balancing cam inside them. The oil pan is the same center sump model found on many industrial engines. It just won't clear most front axles of any type.

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MaxPF

· #124 · 3 d ago

It looks like those balance shafts have slugs of tungsten alloy pressed in them. My guess is that they are worried about a slug being thrown from the unit. Either that or maybe they are concerned about the amount f force applied to those four extra-long main bolts? I dunno. Seems odd to build something with such a small margin of safety.

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cliffpoint

· #125 · 3 d ago

What you are looking at are shafts with holes threaded, and bolts holding on half circle weights, more clearly seen at the
left end of the picture.

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char1355

· #126 · 3 d ago

Over the years Cummins improved on the design of those balancers. Here's one that was used on the ISB/QSB 4.5 engine. Cummins part 2831353. This one acts as a complete bottom end girdle and I'd bet there would be no RPM restriction with it like the earlier style. Of course this one isn't designed for the regular 4bt since the ISB 4.5 is rear gear train and uses a different block. Would be interesting if it would fit. It might fit the ISB 3.9 since it has the same block design. This one only costs $1522.64.

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SUBRUTUS

· #127 · 3 d ago

char1355 said:
Over the years Cummins improved on the design of those balancers. Here's one that was used on the ISB/QSB 4.5 engine. Cummins part 2831353. This one acts as a complete bottom end girdle and I'd bet there would be no RPM restriction with it like the earlier style. Of course this one isn't designed for the regular 4bt since the ISB 4.5 is rear gear train and uses a different block. Would be interesting if it would fit. It might fit the ISB 3.9 since it has the same block design. This one only costs $1522.64.
View attachment 136002

If it tames the beast why not....

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dreamin

· #128 · 3 d ago

MaxPF said:
It should be pointed out that long arms like the above, rigidly mounted to the engine and supported at the frame side, put a lot of bending stress on the block outer walls due to leverage. The Cummins install manual has limits on the bending moment that can be applied to any mount. As a rule, it is best to put the rubber mounts as close as possible to the engine, shortening the length of any support arms and reducing their resulting leverage.

I’ve never seen that. Kind of scares me. Mine are probably right around the 5” max or longer.

Levis said:
Thanks! I’m glad to hear that they are working well for you. Haven’t gone through your whole build but it looks like you have slid the engine rearward quite a bit from the original location, No?
-Levi

Yea, it’s as far back as I could make the rear driveshaft short.

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MaxPF

· #129 · 2 d ago

cliffpoint said:
What you are looking at are shafts with holes threaded, and bolts holding on half circle weights, more clearly seen at the
left end of the picture.

I see it now. Thanks for that explanation. That only strengthens my suspicion that the balance assembly itself can probably handle 3000 RPM just fine, and its the lengthened main bolts that are the weak link. These shafts are supported in the middle, and the casting is quite beefy. Compare that to the balance shaft in a GM 4.3L V6. Those balance shafts are unsupported in the middle, and since they turn at crank speed they can reach 5200-5500RPM peak, which is similar to the speed of the shafts in the Cummins unit.

char1355 said:
Over the years Cummins improved on the design of those balancers. Here's one that was used on the ISB/QSB 4.5 engine. Cummins part 2831353. This one acts as a complete bottom end girdle and I'd bet there would be no RPM restriction with it like the earlier style. Of course this one isn't designed for the regular 4bt since the ISB 4.5 is rear gear train and uses a different block. Would be interesting if it would fit. It might fit the ISB 3.9 since it has the same block design. This one only costs $1522.64.

What document from Cummins states that the RPM limit on the balancer unit is 1800RPM?

dreamin said:
I’ve never seen that. Kind of scares me. Mine are probably right around the 5” max or longer.

That's exactly why I replied to your post and inlined that page from the Cummins install manual. I'd highly suggest redesigning your engine mounts. As I mentioned in that post, you would be better off having a short arm coming off of the engine and sitting atop the fluid mount. The fluid mount itself can be supported on a long arm attached to the frame, provided the stricture has sufficient strength. That includes fatigue strength. Judging from what I've seen, most guys are so overkill on their mounts that strength and fatigue are not a factor.

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