Tag axle pros / cons

The worst thing is people let their MH sit for months. Corrosion starts and that's what eats up low hour engines. I have run Cummins and CAT engines about 600,000 between Overhaul and the reason was it was cheaper to do a major at that mileage than a complete new engine at 1 million.On a 40 ft I'd run 350 HP in line CAT or Cummins. A 3406E CAT is a stong engine. New engines run about 3X an overhaul.got so we just traded in at 400-450K because Cat had a 500K warranty and we let someone else do the work. Also, at around 450K door piano hinges, hood rivets and wear items start giving way. It just comes down to how much you want to invest and what your return is on anything.Tag axles are useless in snow or when it's slick. They do add stability, ran them in the 70s but they tend to bounce around and wear tires more rapidly. If you run pretty hard, say 25K a year the tires still would last 10 yr or more. Our Michelin truck tires go 100,000 mi. Agree with Kayteg, balanced everything makes a longer lasting engine. You need to pull the dynamic balancer and redo it even.

There are no heavy diesels manufactured with RV only in mind.
Most of them are design for heavy trucking and RV use is just side business.
I can only guess, when you ask diesel mechanic about his opinion -it will be based on commercial trucks, not on those few engines used in RV.
Still remember one of the members here reporting that he rebuild old Detroit (in his dump truck?) for about $12k.
Even newer engines save fuel, their cost would take decade to recoup.
Per my experience with wet sleeves, the major difference for RV owners is checking SCA balance. Additional task to do every few months.

SoCalDesertRider wrote:

msmith1199 wrote:

BigD629 wrote:
When I was looking for our DP, I asked a long time Cat Service Tech what he would recommend. He advised me to avoid the C7, as it is a non-sleeved block. I ended up with a 400HP Cummins ISL in a 36'.

Somebody can correct me if I'm wrong, but my understanding is the disadvantage to the "non-sleved" block is it is much more expensive come rebuild time. So after you've put two or three million miles on your motorhome the rebuild would be more expensive?

An engine with wet sleeves, such as the DT466 in my International truck, can be rebuilt with the engine still in the frame of the truck. The block doesn't have to go to the machine shop for boring the cylinders.

You pop the head off, drop the oil pan, remove the rod caps, pull the pistons and rods, pull the sleeves, and put it back together with new gaskets, pistons/rings, bearings and new sleeves.

Also with a wet sleeve engine, because the whole circumference of the sleeve is surrounded by coolant, the sleeve expands and contracts evenly, holding a constant diameter, which extends its usable service life.

With cylinders cast into the bock, there are hot and cold spots in various places on the cylinder. This causes unequal expansion and contraction, which makes the bore out of round, which wears it out sooner.

But again the point being, wears it out in two million miles versus three million miles? If you buy a DP and absent some failure of a part, what are the odds you are going to put enough miles on that engine to wear it out and cause it to need to be rebuilt? I guess there are some people who may put a few million miles on a RV, but not most.

msmith1199 wrote:

BigD629 wrote:
When I was looking for our DP, I asked a long time Cat Service Tech what he would recommend. He advised me to avoid the C7, as it is a non-sleeved block. I ended up with a 400HP Cummins ISL in a 36'.

Somebody can correct me if I'm wrong, but my understanding is the disadvantage to the "non-sleved" block is it is much more expensive come rebuild time. So after you've put two or three million miles on your motorhome the rebuild would be more expensive?

An engine with wet sleeves, such as the DT466 in my International truck, can be rebuilt with the engine still in the frame of the truck. The block doesn't have to go to the machine shop for boring the cylinders.

You pop the head off, drop the oil pan, remove the rod caps, pull the pistons and rods, pull the sleeves, and put it back together with new gaskets, pistons/rings, bearings and new sleeves.

Also with a wet sleeve engine, because the whole circumference of the sleeve is surrounded by coolant, the sleeve expands and contracts evenly, holding a constant diameter, which extends its usable service life.

With cylinders cast into the bock, there are hot and cold spots in various places on the cylinder. This causes unequal expansion and contraction, which makes the bore out of round, which wears it out sooner.

Couple of points of clarification:

- Some MHs do have steerable tags, American Coach being one.
- If you get a 45' tag you will not lose a storage compartment.
- If you get a 42'/43' tag you will lose a storage compartment.

kgard1225 wrote:
Wow, lots of great info here !! Thanks to all who responded. I am definitely looking for more HP than I would have thought necessary. I was kinda thinking anything above 300 would be way more powerful than my current Ford V-10 but I see just about all the pushers weigh more than my gasser. It looks like they are made with higher quality materials . I am now posting another topic on which rigs come with solid fiberglass roofs. I am having trouble with the ads ..... I have to call each ad to see.

I have the 330 hp Cat in my 35 foot DP. It is adequate for my driving, but I think I'm right at the edge as far as having enough power. I have a Dodge Dakota toad so it's on the heavy side, but there are some grades on Freeways in California where I'm down to 45 mph with my foot on the floor. The Grapevine for example.

Tags are a direct relation to weight. I started out only looking at Tags because I thought I would have a bigger carrying capacity, but in reality the tags just means you needed the 30,000 instead of 20,000 lb capacity in Engineering, usually because of >40ft. We ended up with a tag because we liked the floorplan with the bath and a half, but we lost some cargo space below because of the tag. Pick the floor plan you like, and whatever axles it has - it has. We looked at many without tags that were just as nice (some even one and a half bath), they just didn't need he extra axle based on weight.

With the Cummins, I was told to try to get into the ISL (8.9L). That's the 400/450 hp versions. Don't know why, just what my Cummins folks told me.

Fiberglass roofs are the best invention ever made! After decades of caring for those rubber roofs and peeling that lap sealant off of them, it was a real pleasure to go up on a roof with a scraper and roll off that lap sealant in a few seconds and apply new (I just added vent covers and Travler antenna on mine).

Wow, lots of great info here !! Thanks to all who responded. I am definitely looking for more HP than I would have thought necessary. I was kinda thinking anything above 300 would be way more powerful than my current Ford V-10 but I see just about all the pushers weigh more than my gasser. It looks like they are made with higher quality materials . I am now posting another topic on which rigs come with solid fiberglass roofs. I am having trouble with the ads ..... I have to call each ad to see.

BigD629 wrote:
When I was looking for our DP, I asked a long time Cat Service Tech what he would recommend. He advised me to avoid the C7, as it is a non-sleeved block. I ended up with a 400HP Cummins ISL in a 36'.

Somebody can correct me if I'm wrong, but my understanding is the disadvantage to the "non-sleved" block is it is much more expensive come rebuild time. So after you've put two or three million miles on your motorhome the rebuild would be more expensive?

One reason for tag axles is the max allowable single axle load (per the Federal Standards) is 20,000 pounds. And that would be total weight including cargo and any weight a trailer may put on the axle.