390 engine connecting rod

kostean

New Member
Hi,

I was wondering to check if some of the more experienced racers/engine tuners would have anything to say about the strength of the OEM connecting rod of the early 390 engines?

I noticed Carrillo is producing a performance "H beam" rod for 390 engine, but I have really not heard anyone jet commenting having one installed as part of the "normal" performance package (exhaust, thin gasket, intake improvements).
https://www.spearsenterprises.com/product/ktm-rc390cc-carrillo-h-beam-rods-2015-2019/


Does anyone have an opinion on such "H- rod" investment reasonability for track bike? I just admit I know one 2015 year engine what grenade during the first 10 hours of track use as the connection rod broke- but it got suggested to be manufacturing fault of a particular one so I have so far considered the connection rod to be something at the 390 engine design what is not at the top of the list of components to be replaced for racing use.
 

Superpacman13

Supporting Vendor
I've never had a rod snap but I have had 2 rod bolts fail. The limiting factor that I have found has actually been the piston.
 

tylercarbone

New Member
I know chad’s old engine kit had both pistons and rods. It hasn’t been for sale in awhile. When I reached out, was told that it wouldn’t be continued for the foreseeable future. (And that he was sadly out of inventory.)

Carrillo indicated a few weeks ago that they’re happy to do a custom run of both, but I haven’t had a chance to pursue it further at all.
 

kostean

New Member
What a bummer that noone does offer any more performance engine internals for 390. That leads eventually KTM-s been replaced by Kawasaki and Yamaha on the supersport class to continue only as a street bike.

Though, if anyone knows where to get reach of engine components similar what Chad had formed up as a kit- I would be certainly interested.
 

ChrisW

New Member
I would be interested in the piston/rod combo from carrillo if anyone else wants to talk about getting an order together to make it worthwhile. I saw a picture once of a single compression ring piston which I thought was very interesting. I’m quite new to the forum and I have commenced a full build on a new 2020 model. Hope we can put something together for the benefit of all.
cheers, Chris
 

kostean

New Member
Hi Chris,

Well, it you are seeking for interested ones then I am in.

Chad had the single ring piston at his engine kit as far as I recall, from where were these made of course we don't know. I have been asking a couple of times since the beginning of the year are there any chances this 390 engine kit will be brought back to the sale, but with corona and Kawa/Yamaha being now the favoured racing platforms, there lacks a motivation probably for him on putting these kits together again.
 

ChrisW

New Member
I am chasing up a guy here in Australia who designed his own cam profiles and had promising results with associated head work and increased compression.
I will report back if I have any luck.
 

tylercarbone

New Member
Response from Carillo pasted below. They also confirmed in a later email that the price would be the same if I needed any changes made from stock.

Quoted price was for 1; I didn’t inquire about any discount for more. Unsure how this compares to the prices from chad’s old kit.

Carillo reply:

We can make them as customs if needed, rods are $409.50 each lead time is 8-10 weeks and pistons would be $300.00 each with lead time at 5-7 weeks.
 

ChrisW

New Member
I have had custom JE pistons done previously for a different project and they are excellent. My engine machinist was very impressed with the tolerances.
Merry Christmas to all.
 

tylercarbone

New Member
I had inquired about pistons that were bigger bore, as Chad had posted a few years ago about having gone in this direction, but recent advice is that sleeves too thin.

(Again, haven’t had time to look into further, but that had been my intention a month or two ago when starting this build.)
 

ChrisW

New Member
Bigger bore is something I would like to do as well. I’m not sure if the barrel has enough meat to do it, but it is feasible to bore and re-plate an aluminium cylinder.
If someone has any knowledge about cylinder bore thickness I would be interested to know. Again, in Australia, we have several companies renowned for there quality of work when re-plating nikasil barrels.
Good to hear that there are people still interested in developing the 390 engine.
 

kostean

New Member
Bringing this thread bit higher after the year change. Superpacman13, don't know were there any reply to your e-mail sent previously. But if it becomes reasonably priced if we order more custom made pistons with a single ring, then I would list for a pair for sure.

I would seek them on original bore size though, no to reduce the reliability of the engine and to be able to fit these pistons to engine out of the box.
 
Last edited:

ChrisW

New Member
Hi Kostean and Superpacman, I’m in for that. Happy to do standard bore too. I guess there must be reasons why the big bore development didn’t go anywhere.
 

ChrisW

New Member
If you look on the wiseco website they have information about single ring pistons and discuss how Honda achieved this with their CRF through specific ring design.
 

kostean

New Member
What of course would bring up a question- on what ways would be the single ring piston superior to the OEM one. My consideration is that single ring piston could reduce the friction by some degree and might be made to increase the compression ratio by some degree when used with a standard head gasket. With a thin gasket- it is already a question wouldn't the compression ratio to be getting too high.

Just following that once Chad had the engine kit on sale, included piston at that one was a single ring one- so there probably was a good consideration why it was made so.
 
Top