Rotax 277 piston port to reed valve conversion

[kawicat]

I used to do quite a bit of side work on peoples things and I had a guy ask me if I could make his boat run better so I told him yes his boat had twin small block 350 Chevrolet engines in it so I bought four sets of spark plugs for his engines and out of 32 plugs I was able to index 16 of them correctly in the engines combustion chambers and I recurved the centrifugal advance in both HEI distributors in his engines and he paid me with penny stocks a bunch of them, at first I was not going to take them as payment but he was a trusted friend of an acquaintance of mine so I took them as payment, I have a friend that is a stock broker and I gave them to him to see what they were worth so after a day or so he called me and said that some of them were worth some good money and some were not worth anything at the time so I asked him if I should just hang on to them and see if they would be worth more in time and he replied " The hogs get slaughtered in this game" so I told him to sell them for me and he did and when he gave me the check for the sold stocks I about sh-t! I was floored to say the least! I had to pay income tax on my earnings but that was well worth my time and effort and the guy was tickled with his boat and that is how I made over 8000.00 on a tune up.

Well then you certainly were in the right place at the right time!

 

[Desertduler]

Well then you certainly were in the right place at the right time!

Yes, but that does not happen to me very often!

 

[Poboy kartman]

No kidding...I'm. the the guy that bends over a curb to sniff poodle......

 

[Desertduler]

While I have this engine torn down I am going to replace the connecting rod with this one it is like new, the original rod is showing some wear in the wrist pin bore which is due to not having a cageless bearing installed on the wrist pin when the engine was new, I will press the crankshaft apart and install this rod and use a cageless wrist pin bearing.

 

[kawicat]

will you use a cageless lower rod bearing too?

 

[Desertduler]

will you use a cageless lower rod bearing too?

No, the big end bearing on these engines are pretty much bullet proof, the weak link with this engine is the small end of the connecting rod as the bearing surface metal at that location will flake and pit if a caged bearing is used over time, with the cageless bearing there are double the amount of needle bearings so the load on the small end of the rod is spread out more and the rods last a long time with the cageless bearings installed. The original rod that I am replacing was worn to a degree but still in spec and I planned on replacing it with this low hour rod at this time and use the cageless bearing set up from here on out.

 

[Desertduler]

Here are a couple of pictures of the failing connecting rod, I had a new one on order from Rotax for over a year which was back ordered and then they told me that they were not going to produce any new ones so I had to hunt down spare crankshafts in order to find this engine a good connecting rod and I lucked out and found two pristine crankshaft assemblies which had point ignitions which has the wrong flywheel taper and key phasing to use with a CDI ignition so I have to press them apart to remove the connecting rods and have them as spares to use with my CDI crankshaft which I run in this engine. Here is the cageless wrist pin bearing on the left with a plastic sleeve around it and the caged bearing on the right which when used with this engine will cause premature wrist pin bore failure which this engine had came with to begin with hence the start of the rod failure.

 

[Armilite]

Cageless Bearings

No, the big end bearing on these engines are pretty much bullet proof, the weak link with this engine is the small end of the connecting rod as the bearing surface metal at that location will flake and pit if a caged bearing is used over time, with the cageless bearing there are double the amount of needle bearings so the load on the small end of the rod is spread out more and the rods last a long time with the cageless bearings installed. The original rod that I am replacing was worn to a degree but still in spec and I planned on replacing it with this low hour rod at this time and use the cageless bearing set up from here on out.

=================================================
If you really want it Bullet Proof, make your own Cageless Lower Bearing. Take (2) lower bearings and cut apart for the rollers, and then make (2) Hardened Rings just like the Upper Rod Cageless Bearings. It's the Cages that Fail!

Also, use a Rod that has Dual Oiling holes on Top, with Dual Oiling Slots on bottom.

I see your using the Moly Coated Sidewall Piston, have the Top of the Piston, the Head Combustion Chamber, and the Cylinder Exhaust Port, and Pipe Connection, all Ceramic Coated, and you, and your Engine will be much more happy! There is also a Heat Dispercent Coating that is Black, you can Coat the Outside of the Head, Cylinder with that also helps it to run Cooler.

Just My 2 Cents

 

[Armilite]

A Rod like this. Another Failure Point is the 1mm Side Shims, if you can find some Ceramic one's, they can handle the Heat better. There is also Half Ceramic Crank Bearings, Steel Races with Ceramic Balls.

 

[Armilite]

Ceramic Coated Top, Moly Coated Sidewall Piston.

 

[Armilite]

Coated vs Uncoated from same engine.

 

[Desertduler]

=================================================
If you really want it Bullet Proof, make your own Cageless Lower Bearing. Take (2) lower bearings and cut apart for the rollers, and then make (2) Hardened Rings just like the Upper Rod Cageless Bearings. It's the Cages that Fail!

Also, use a Rod that has Dual Oiling holes on Top, with Dual Oiling Slots on bottom.

I see your using the Moly Coated Sidewall Piston, have the Top of the Piston, the Head Combustion Chamber, and the Cylinder Exhaust Port, and Pipe Connection, all Ceramic Coated, and you, and your Engine will be much more happy! There is also a Heat Dispercent Coating that is Black, you can Coat the Outside of the Head, Cylinder with that also helps it to run Cooler.

Just My 2 Cents

One of the drawbacks of having a cageless bearing on the big end of the connecting rod is that as the bearing rotates around the rod journal pin and the rollers are in contact with one another and the surfaces that are touching each other are moving in opposite directions and this creates more friction and drag unlike if the rod bearing is caged, try rubbing two cylindrical objects that are the same size as on another together on a surface and have them touch one another as they are rolled and one can see this happen, plus caged bearing rollers tend to roll true without cocking slightly over surfaces, the wrist pin bearings are subjected to oscillating movements not rotating so a cageless bearing works in that location without inducing a lot of friction, I have tried ceramic coated pistons before in a snowmobile that I used to have, it was a Arctic Cat ZRT 800 which was a three cylinder two stroke and for the money that I spent for the pistons I would have been better off spending my money some where else as I did not notice any benefit in performance or durability over quite a few seasons of use, I have always been a stickler with jetting and adjusting air fuel ratios according to current conditions that an engine is subjected to and reading spark plugs and looking at piston wash in order to get the maximum performance and life out of any two stroke that I have owned that was either a race machine or a play machine and feeding all of them top quality oil and so on. There are no new connecting rods available for this engine and I have never came across a dual slotted rod for a 277 Rotax but then again I have not seen everything.

 

[Poboy kartman]

Ya know Brett....I don't go up against folks as knowledgeable as you often....but I really can't see cageless needle bearings as producing any significant drag....

In theory anyway...maybe caged bearings have less drag....BUT... cageless bearings are rolling around on round and round to round....the very reason that they were incorporated into high screaming 2 sickles.

So...while caged bearings do reduce the amount of contact surface involved....the quality of such contact surface is suspect in my mind....

I suspect the reason they may work better in the long haul is that as clearances grow....uncaged bearings can "gang" together and create an oval bearing surface.

Just speculation....but my theoretical musing....

 

[Desertduler]

Ya know Brett....I don't go up against folks as knowledgeable as you often....but I really can't see cageless needle bearings as producing any significant drag....

In theory anyway...maybe caged bearings have less drag....BUT... cageless bearings are rolling around on round and round to round....the very reason that they were incorporated into high screaming 2 sickles.

So...while caged bearings do reduce the amount of contact surface involved....the quality of such contact surface is suspect in my mind....

I suspect the reason they may work better in the long haul is that as clearances grow....uncaged bearings can "gang" together and create an oval bearing surface.

Just speculation....but my theoretical musing....

There may not be a lot but there is some, at high rpm not much oil hangs around on two stroke rod bearing rollers and the least amount of friction the better, there is a reason that caged roller bearings are used for the big end of the rod bearings, everyone has their opinion and not everyone builds their engines the same and sometimes that can make the difference in the longevity of a engine, there were plenty of old two stroke engines that used cageless big end bearings but not so much anymore, KTM still makes two stroke racing motorcycles and I consider their engines as some of the best two stokes ever made and very durable, you won't find any cageless big end bearings in their engines or any later model two stroke snowmobile engines either.
To each their own I will build my engine to what I think works the best that is what keeps most of us unique and not cookie cutter like.

 

[Poboy kartman]

Ahhhhhh....that's the other shoe!!!! It's not friction , but oil starvation! Now it makes more sense! It's not friction reduction, but making space for oil that is the real benefit! (And for some silly reason, some folks think oil reduces friction!)

Thanks man! Another 100 things to learn and I'll almost be smarter than a 3rd grader....

 

[Armilite]

One of the drawbacks of having a cageless bearing on the big end of the connecting rod is that as the bearing rotates around the rod journal pin and the rollers are in contact with one another and the surfaces that are touching each other are moving in opposite directions and this creates more friction and drag unlike if the rod bearing is caged, try rubbing two cylindrical objects that are the same size as on another together on a surface and have them touch one another as they are rolled and one can see this happen, plus caged bearing rollers tend to roll true without cocking slightly over surfaces, the wrist pin bearings are subjected to oscillating movements not rotating so a cageless bearing works in that location without inducing a lot of friction, I have tried ceramic coated pistons before in a snowmobile that I used to have, it was a Arctic Cat ZRT 800 which was a three cylinder two stroke and for the money that I spent for the pistons I would have been better off spending my money some where else as I did not notice any benefit in performance or durability over quite a few seasons of use, I have always been a stickler with jetting and adjusting air fuel ratios according to current conditions that an engine is subjected to and reading spark plugs and looking at piston wash in order to get the maximum performance and life out of any two stroke that I have owned that was either a race machine or a play machine and feeding all of them top quality oil and so on. There are no new connecting rods available for this engine and I have never came across a dual slotted rod for a 277 Rotax but then again I have not seen everything.

==========================================
All I can tell you is some Boat motors use Cageless Bearings on the bottom big end, and I know Rotax Rick who builds on average about 150 Rotax engines a year, has been experimenting with them on his Skidoo/Rotax 670(92hp) Conversions for Airplanes with good results. True Top Bearing rock back an forth, bottom bearings spin. It's the thin Steel Cages that Fail, not the Bearing Rollers. On Cageless Bearings they can't cock sideways, each roller keeps them in place with a little clearance. The engine companies have tried Bigger Caged Bearings 26mm crank pins to 27mm crank pins, which just increase the rotational speed of the bearing.

Ceramic Coating, and other Coatings are for durability, and reducing Heat, but they do allow you to run the engine a little harder before you melt it down in Racing applications where the engines are pushed to their limits. You can do most of it today at home with a Free Electric House Stove off Cragslist. Techline Coatings and others sell the products. Most Coatings only need to bake at 300-350 degree's, only Ceramic needs, I think 750 degree's. Most self clean electric stoves can be adapted to do that. If you do all the different Coatings your engine can run 20% Cooler. Heat affects all your parts, Seals, Oils, etc. to do there job. Some Coatings reduce Friction, like on Gears.

Bullet Proofing a 503
http://www.challengers101.com/Bulletproofing503.html

Ceramic Crank Bearings run Cooler, and need less Oil, than Steel Conventional Crank Bearings.

I haven't found anyone either who makes a New Double Slotted rods for 277's. But you can adapt another Rod & Piston. 277(120mm), 503(120mm), 521(125mm), use the same 72mm Piston. They almost all used a 24mm Crank Pin back then. 2003+ 380F, and 550F, both use the same 120mm Rod, which is 2mm wider than a 277/377/503 Rod, which the 2003+ 380/550 Rod uses a Bigger Top Bearing than the 277/377/503 18mmx22mmx22mm used. So you can ream a 18mm 277 72mm piston for the Bigger 380/550 20mm piston pin, ad recut cir clip slot deeper. Use the 550(76mm) Piston and 550 Rod to make a 277 Big Bore.

(76mm x 66mm) 299.5cc

Just My 2 Cents
Rich

 

[Desertduler]

Good information on the engines with 120mm rod lengths, thanks, I will keep that information for use in the future in case I run out of 277 con rods, I can indeed ream the 18mm bores in the stock pistons to 20mm and groove the reamed bores for wrist pin clips providing I think that there would be enough material left in the piston wrist pin boss areas after reaming the bores to 20mm.
I would test ream an old piston first to check it out.

 

[Desertduler]

The connecting rod on the right is 17mm wide which is used with engines with CDI ignition crankshafts, the connecting rod on the right is 15mm wide which is used with engines with points ignition crankshafts.

 

[Desertduler]

In this thread I failed to show how I adapted the reed block housing to mount to the machined reed valved cylinder, I have had a few people ask me to show them how I did it so here you go.
https://www.youtube.com/watch?v=J0VeawwJ_6A

 

[rodney007]

https://www.youtube.com/watch?v=ULhf-QzqSLQ

looks fast