What porting is this? What should I do?

[Speedfreak]

I just bought this ski and it turns out that the motor is a LOT bigger than I thought. The cylinders have 61X stamped on them but I am not sure where they came from. It is in the center under the exhaust manifold. So does that make it a 701 cylinder? How can I tell if it is a 760 cylinder. Is there enough meat left in the cylinder.

Here are the pictures and the bore is 85mm. These are from my phone so they don't show the most detail but you get the picture. Also the transfers are ported pretty good as far as I can tell. The motor runs and I was told that it runs strong. So I didn't want to tear it down.

 

[Matt_E]

If it's stamped 61X, then it's originally a 701 cylinder.
It may have been resleeved for bigger bores. What is the current bore size?
I've seen that exhaust porting on some Pro-Tec jobs.
Is there no inscription on the cylinder anywhere?

 

[Speedfreak]

The bore diameter is 85mm The 65u pistons are 1mm over bore I guess from the 100 stamped on the crown of the piston. There is a 82 scribed on the base between the pto carb and the cylinder wall but that is the only marking. The cast has a 64vI think? on the id tag what case it that?

It has a girdled head so I guess it should be ok as far as reliability.

Also should I tear it down the rest of the way and hone it for that tiny bit of surface rust? The cross hatch pattern is very visible and the head has NO build up at all. I was told that it only has a bout a tank of fuel through it. The guy had a problem with the pump and lost interest before he got it dialed in.

 

[GIL]

Those look identical to my neighbors 61X cylinders that I pulled yesterday that were ported by Dallas Baker of Pro Tec. Her cylinders say DBP on the right frt corner of them.

 

[grezzmky]

JR, Id say if you are going to hone them yourself leave them alone. If you really want the piece of mind then get some new rings and take it to the machine shop for a hone to get the corect angle on the hone. Did you check compression first? My jetworks cylenders look worse then that after less then one season (no rust but lots of vertical wear scratches).

 

[MADMAT]

Man bolt that thing back together and ride the living chit out of it. It sounds like you have a set of couch cases (is it dual 44 carbs with dual pulse lines?) with 61x cylinders re sleeved to big bore! Rip it!

It does not need honed at all IMO.

 

[junkyardj]

i have a similar exhaust port setup on one of my pro tec cyl's

 

[Big Kahuna]

If you cannot hone a set of cylinders and put it back together.......

pffffttttttt.

 

[XFT LOU]

I'm with MadMat on this one, since I was there when you bought it. Leave it alone! Fix the cracked plastic part because I can see into the future: Its now Aug. 2010 Jr's skis has been disassembled for 6 mth. and he's working on a golf kart and not ski'ing.

 

[Foximus]

Man, seeing that porting would drive me crazy... that just looks like its screaming to catch a ring.

 

[Kalwren]

Man, seeing that porting would drive me crazy... that just looks like its screaming to catch a ring.

You'd be wise to listen to Fox on this one. He's ported both the engines I use and they run great. Fix it right and ride it with a peace of mind.

Don't be "that guy" wrenching on the beach.

...Fix the cracked plastic part because I can see into the future: Its now Aug. 2010 Jr's skis has been disassembled for 6 mth. and he's working on a golf kart and not ski'ing.

..and listen to XFT Lou. Don't set it on the bench and get distracted by the next shiny thing.

 

[Big Kahuna]

You'd be wise to listen to Fox on this one. He's ported both the engines I use and they run great. Fix it right and ride it with a peace of mind.

Don't be "that guy" wrenching on the beach.




..and listen to XFT Lou. Don't set it on the bench and get distracted by the next shiny thing.

Trust Fox or Trust Dallas Baker with Protec...............


Hard decision.

 

[junkyardj]

Trust Fox or Trust Dallas Baker with Protec...............


Hard decision.

lol

 

[steve-uk]

Man, seeing that porting would drive me crazy... that just looks like its screaming to catch a ring.

im interested..... where will it catch?

 

[Big Kahuna]

if I am not mistaken, Protec does not touch the width much unlike alot of the Freestyle Porting guys do. Where they enlarged it really is not much wider than say how TLR or XScream may port it. Those two indentions kinda act as a Boost. ( I dont have the technical term for how it helps - or if it really helps much, but Protec has been around long enough to know what works and what does not).

If your port gets to wide, the rings can "Push" out when the pisten passes into the port window causing the ring to "bulge" out, on the upstroke the ring could snag on the roof causing damage to the cylinder, piston and or rings.

 

[Foximus]

Ok, I'll say this now.

I dont know the actual dimensions of the port so I cant say what exactly is what... And I'm by no means saying thats a cylinder...

However I will say that, just looking at the pictures it catches my attention as a poorly designed port. Why would you have two extra eclipses into the side of the port that low into the duration? Not only that but there seems to be very sharp edges on the lower and upper corners of those eclipses... Now I'm sure they are chamfered but still...

Whats the point of having further perpendicular perimeter when the overall port surface area is not that greatly increased? The more perpendicular (0* angle) area there is to a port the more chance there is of snagging a ring. I would much rather have the entire port widened only 2mm in a big radius fashion as opposed to a ~4mm semi-circle in the middle of the port where piston speed is the slower, and more time is allowed for the ring to skip out. (though that in itself may lend itself to having more time for gas exchange) To me this just seems as a way to circumvent getting around the "safe" 71-73% rule, but if you ask me a better way to do this would be an upside-down Trapezoidal port. This would allow you go up to 75-77% of the bore for a more effective duration.

Not only that, but airspeeds are kept at a minimum when there are square edges. Velocity is promoted by having nice round and radius-ed edges... So the inner corners are really not flowing air. Overall I see those extra additions as just Dead-space.

Slight edit... I typed to fast and mixed up the relative PS's. Fixed.

 

[Foximus]

On a side note, Id really like to know what those black boxes are on the lower right hand corner of the transfer ports... I cant tell from pictures.

 

[Speedfreak]

I will measure the port size and get some better pictures. The motor is setup with a protec intake and has 46mm Buckshots and a speedwerx pipe. So I would guess that it is a complete Protec setup. it only has 155 psi of compression. I would like to jump that up 40 psi or so but without knowing the porting I am keeping it where it is. The squish is .055 I don't know what size the domes are I am going to have to cc them this week to get an idea. They have no markings and neither does the head.

How should I measure the ports other that distance from the top of the cylinder and the over all width and height.

 

[waxhead]

Its a protec cylinder or a copy for sure
They also used to port like this on the old mecury race outboards i am lead to believe.From what i can gather it worked on engines that didnt have an expansion chamber
I hate it , its just asking to smash rings or at promote ring land wear vey fast which will alow the ring to slop and then smash.
Why , because the ring will be going in and out so fast as there is no lead into to move the ring slowly. Before anyone else says protec were a force and they would know. They were a force and they were leading edge in there day, but powerful people used to think the earth was flat too.
Its old style porting , all sorts of weird things were being tried back in the day but now it seems we have gone back to the more conventional style porting.
I would measure the port at its widest and then if its not to wide i would take the cylinder and get the exhaust port fixed it will be a nicer engine with more power.

 

[waxhead]

On a side note, Id really like to know what those black boxes are on the lower right hand corner of the transfer ports... I cant tell from pictures.

Shadows from the flash