black mamba

Ok. I just got one of each off of ebay and I don't know which one to keep. My wife said I can only keep one. LOL, so I'm asking the guys that have them, which one is the better engine. I'm not just looking at all out power, but rather reliability and tuning stability as well as I plan on racing this spring/summer.

Chronic

How about pulling both of them apart and showing us some side by side pics of the internals... I know some people don't like to tear them apart for such a trivial issue, but it would clear up a lot of arguments. They are the same essentially the same engine, but the Axial has made slightly more power than the K4.6 in two dyno tests now... I'm sure it's just a matter of different head clearance or testing procedures, but some people claim that the two engines do have some differences. I'd really like to see some comparison pics if possible.

I would keep the Axial though. The HPI has a higher retail cost new, so it makes sense that it should carry a higher resale value.

HerrSavage

LOVING my Axial 28... SO easy to start.. - so far..

benzzyo5

i never had the k4.6 but i have the axail .28 and i really like it. easy to tune hold's a pretty good tune, and cuz of that it does make it easy to start. break-in went very smooth. i would just go with the axail

black mamba

Thanks for the replies! Keep them coming. As of right now, I'm leaning towards keeping the Axial and letting the K4.6 go.

Chronic, if I can stomach tearing apart two brand new engines, I'll post pics.

Vigilante212

You should always take a new engine apart just to flush the insides out with nitro cleaner to remove any leftover debris from manufacturing, youd be surprised what can get left in it.

SAVAGEJIM

I cannot agree more with this here. There is so much machining debris left over that you will be surprised that most other brand new engines that are broken in without this cleaning are not ruined.

Also, when reasembling a brand new engine after this cleaning, take the opportunity to RTV seal it to attack any possible air leaks.

Crzybri82

Keep the axial. I just got one last fall and in the time that i was able to run it before snow fall, the thing was just awesome. Its easy to work with and most of the HPI parts are compatible with the Axial.

black mamba

Here they are side by side. I'm not going to pull the K4.6 apart as I will be selling it and want to keep it "virgin" for a honest sale. The Axial was rinsed and blown out...good enough for me.

black mamba

That's the one I went with. What heat range plug are you using in yours? I'm going to be running 30% fuel, so I was going to start with a cold plug and see how it ran.

Here it is in the truck, just waiting on the CB to come in so I can wrap up the installation.

benzzyo5

i run an hpi med-cold plug with mine, and i use 20% i like this plug if you want to use a cold plaug which you probably are use a hpi cold plug http://www2.towerhobbies.com/cgi-bin...?&I=LXFYM4&P=7

jcam54

I don't have the k4.6 but I have a Axial 28 and I took it apart for yall to compare with pics of someones k4.6. Have to post again to get all pics in.

jcam54

here's the rest

Chronic

Thanks for the pics jcam. I wish I had a K4.6 so I could post some pics of it for comparison.

From what I can remember though, that sleeve is just like the one in the K4.6

-SomeGuy-

Pics of my k4.6. They look exactly the same to me. The conrod didnt want to let go of the crankshaft and i dont have pliers small enough to remove the piston from the conrod so thats as far as i could take it apart.

Chronic

Cool, we have pics!

benzzyo5

^^^ yeah the arguing is over.............this should be a sticky......lol

jcam54

i was just checking out towerhobbies and looked up the k4.6 parts listing and the o-ring set looks exactly like the set i need to get rid of my air leak at the backplate!!! Mine is a little squished and chewed up.

these are almost exactly the same motors!! It wouldn't surprise me if the crank has a little more porting on it like thr k4.6HO...sounds like there was some truth to what a lot of people where saying!!

here is the parts listing

http://www2.towerhobbies.com/cgi-bin...I=HPIG1501&P=Z

benzzyo5

just use rtv copper sealant to seal anything on your motor

jcam54

thanks Benzzyo5
I do, but I like to leave the o-rings inplace and use permatex copper rtv. There is a o-ring for the coverplate where it meets up to the block houseing and I want to replace it and also seal with the rtv

benzzyo5

ok, thats a good idea, you are garenteed not to have an airleak

jcam54

I think you posted a link to instuctions on how to seal up a nitro and it said to use all the o-rings so I figured i'd wait and get the new o-ring set and then seal her up tight.

benzzyo5

this is the one i use for a link http://www.phpbbserver.com/rcworld/v...mforum=rcworld

SAVAGEJIM

From the dimensions I measured on the K4.6 crank and a K4.6 HO crank I bought, both cranks are exactly the same. Now, the induction timing of the HO might be different by the width of the induction port in the HO block itself.

Based on the pics you guys posted, the Axial sleeve appers to have the very same configuration as the K4.6 (non-HO). However, the forward lateral ports seem to be staggard up some in related to the rear lateral port. Also, the 4 lateral ports appear to be longer up and down so they would have a larger flow area when fully open.

In addition, the K4.6 cranks only have one lube groove ring which is cut in front of the crank induction port. The Axial crank has an additional lube groove ring cut behind the induction crank port. I wonder if the Axial crank uses harder material than the K4.6 crank? the K4.6 cranks are softer and when a flywheel nut is tightened down on it, the crankshaft distorts some such that when you pull apart the K4.6, you need a rubber mallet to tap out the crank. A quality hardened crank would not distort like this and will slip out by pulling with only the fingers.

I know you do not want too much hardness on the crank especially in the conrod pin because the conrod pin would become brittle and the shear forces would cause it to shear off. Nitrostar could remedy that by doing what other companies have done (such as Picco or the Rossis): they could have gone to a pressed-in conrod pin so the conrod pin would retain some softness to handle shear forces by "giving" a little (at the molecular level) and not shearing off as easily. The crank itself would be more resistant to the distortion I mentioned above. For as much as what K4.6's sell for, the engine deserves this additional manufacturing process. I think it is lame that an Axial .28 engine can be had for nearly $40 less (in some cases) than a K4.6!

jcam54

True but I laughed all the way to the bank. I love this motor and am extremely happy with the bang for the buck ratio I have gotten out of it.

Great write up savagejim!

I was happy to put the pictures out there for you guys.