There is a guy in Leeds, ME that used to mill out 670 jugs to shoehorn in Cat ZR-900 pistons. That is one of the many mods he did to the 670s. He had a trail modded MXZ 670 that would take down a stock RT chassis Mach Z.

His family used to own Reggie's Ski-Doo & Kawasaki.

 

The problem with using a liner large enough to have a 85 mm bore in a 670 is the liner protrudes into the transfer port so far that the poor transfer port flow will offset the gain from the larger bore!

We have found that even the 82 mm liners are border line on getting flow to gain real good top end performance! I
f you want to understand what I am talking about look at a 700 F series arctic Cat engine and you will see how large the transfer ports are in that engine, it is easy to see why the 700 Cat makes so much power for its size.

 

There is a guy in Leeds, ME that used to mill out 670 jugs to shoehorn in Cat ZR-900 pistons. That is one of the many mods he did to the 670s. He had a trail modded MXZ 670 that would take down a stock RT chassis Mach Z.

His family used to own Reggie's Ski-Doo & Kawasaki.

Thanks. 82.5mm was the biggest I had ever heard of them Big Bored. I got a set of 81mm Cylinders waiting for a new project.

 

The problem with using a liner large enough to have a 85 mm bore in a 670 is the liner protrudes into the transfer port so far that the poor transfer port flow will offset the gain from the larger bore!

We have found that even the 82 mm liners are border line on getting flow to gain real good top end performance! I
f you want to understand what I am talking about look at a 700 F series arctic Cat engine and you will see how large the transfer ports are in that engine, it is easy to see why the 700 Cat makes so much power for its size.

Ya I thought his ad was a Type O when he said 85mm, 82.5mm was the biggest I had ever heard of, but I e-mail him and he confirmed it that 85mm was right. Sounds like it isn't worth the trouble. MY thinking was Max CC for Max 6500rpms use.

 

Ya I thought his ad was a Type O when he said 85mm, 82.5mm was the biggest I had ever heard of, but I e-mail him and he confirmed it that 85mm was right. Sounds like it isn't worth the trouble. MY thinking was Max CC for Max 6500rpms use.

It depends on what you intend to do with the Engine if you are looking for a torque monster I could see using the 85 mm liners if you keep the RPM down ! I have one that I Built special for a groomer engine it has 82 mm bore with 70 mm stroke for 740cc. I lowered the port.080 to shorten the port timing the engine runs at 7200 and is happy to idle all day, or pull like Bull in the low RPM range for this kind of power the transfer ports wouldn't be a problem.

What I
use for pistons in the Big bore are ProX they are for a 787 Water craft or for a 717 water craft if your using a stock height porting!

These pistons are available in 82mm Standard or in 10. 20 .30 and 40 over size .

 

It depends on what you intend to do with the Engine if you are looking for a torque monster I could see using the 85 mm liners if you keep the RPM down ! I have one that I Built special for a groomer engine it has 82 mm bore with 70 mm stroke for 740cc. I lowered the port.080 to shorten the port timing the engine runs at 7200 and is happy to idle all day, or pull like Bull in the low RPM range for this kind of power the transfer ports wouldn't be a problem.

What I
use for pistons in the Big bore are ProX they are for a 787 Water craft or for a 717 water craft if your using a stock height porting!

These pistons are available in 82mm Standard or in 10. 20 .30 and 40 over size .

Yes, for a Torque Monster at low 6500-6750rpms Max would be for my use. Do these PWC 82mm Pistons work on standard 670 Rods or need 670HO Rods? Or do they still need modified ? I have a pair of 670 Big Bore 81mm Cylinders I got off ebay, I may need to Bore them to maybe 82mm.

 

Yes, for a Torque Monster at low 6500-6750rpms Max would be for my use. Do these PWC 82mm Pistons work on standard 670 Rods or need 670HO Rods? Or do they still need modified ? I have a pair of 670 Big Bore 81mm Cylinders I got off ebay, I may need to Bore them to maybe 82mm.

The water craft pistons will fit ether 670 rods you just need the proper Wrist pin bearing, the pin is 20mm! For a stock liner You would need the 717 piston !

 

The water craft pistons will fit ether 670 rods you just need the proper Wrist pin bearing, the pin is 20mm! For a stock liner You would need the 717 piston !

Ok, Thanks. What's the Biggest Big Bore you have seen done on a 583/617?

 

Ok, Thanks. What's the Biggest Big Bore you have seen done on a 583/617?

At one time Wiseco sold a piston to bore to 78 and a big bore liner to 80 but it didn't last vary long before it was discontinued !

The 650 Sea Doo Water craft has the same stroke as a 617 but the pin size is 20 mm on the 650 and the deck of the jugs are taller than the skidoo engine.

 

At one time Wiseco sold a piston to bore to 78 and a big bore liner to 80 but it didn't last vary long before it was discontinued !

The 650 Sea Doo Water craft has the same stroke as a 617 but the pin size is 20 mm on the 650 and the deck of the jugs are taller than the skidoo engine.

Ok, ya I found a site a few years ago that talked of a 79.4mm 583 Big Bore with a Weisco Piston part number, I want to say it was Western Power Sports who was offering it back then. Wiseco said it was Special Order back then. Did Wiseco also make the Big Bore 80mm Sleeve, or was it a Custom made one? Yes, I thought of using the Seadoo 650/657 78mm Piston and the 650/657 125mm Rod to go with. A Spacer Plate could be made to make it all line up right. I got a 650/657 78mm Cylinder that fits on a 670 case, but two Cylinder bolts don't line up. They could be welded up and redrilled/tapped. Haven't tried them on a 583/617 Case yet. Waiting on my Case Boring Tool. For my use, Max 6500-6750rpms the 583 Rave Valves probably wouldn't really benefit me that much. I would rather have the Max Bore I can get. Trying to figure out how to get a 670 Crank to fit into a 582UL Case right now.

583 BB (80mm x 64mm) 643.7cc

617 BB (80mm x 68mm) 683.9cc

 

rotaxflyer, Do you know where i can find the 670 bigbore 82.5mm pistons??

 

" I lowered the port.080 to shorten the port timing the engine runs at 7200 and is happy to idle all day, or pull like Bull in the low RPM range for this kind of power the transfer ports wouldn't be a problem."

Just a question: How do you lower the port .080 ?

Need data about this set up. Carb size and diameters of the RV cover if possible, thanks a lot for details.

Hard to get data here in Germany, because we have no sleds here like you

Greetings from Germany

Agria Speed Freaks

rototiller racing 670 powered

 

rotaxflyer, Do you know where i can find the 670 bigbore 82.5mm pistons??

eBay is where I see them.

 

" I lowered the port.080 to shorten the port timing the engine runs at 7200 and is happy to idle all day, or pull like Bull in the low RPM range for this kind of power the transfer ports wouldn't be a problem."

Just a question: How do you lower the port .080 ?

Need data about this set up. Carb size and diameters of the RV cover if possible, thanks a lot for details.

Hard to get data here in Germany, because we have no sleds here like you

Greetings from Germany

Agria Speed Freaks

rototiller racing 670 powered

Here is a comparison of a Skidoo/Rotax Standard 335 Single (78mm x 70mm) 334.5cc vs the 340 TNT Single (78mm x 70mm) 334.5cc Intake Ports. The 340 TNT Intake Port is 2.5mm / 0.0984249" Lower than the 335 so have different Port Timing.

Usually, you can make Stock Ports a little wider with no changes to Port Timing. As you can see the Stock Standard 335 Intake Port is 26.5mm x 47mm and it can go to 51mm. The 340 TNT Single is 29mm x 47mm and can go out to 51mm also.

I believe for the 670 there is 3-4 different Rotary Valves. Cylinder & Case Porting can make 10-15% more overall Hp. You do have a Standard 670 11.5cr made 1992-1999 115.7hp@7750rpm and a 670HO 12.5cr made only 1998-99 also.

There was some good Porting Photo's of a Skidoo 670 on https://2-stroke-porting.com/ and there were some Porting Templates floating around, I think Ken O Conner bought them out.

 

" I lowered the port.080 to shorten the port timing the engine runs at 7200 and is happy to idle all day, or pull like Bull in the low RPM range for this kind of power the transfer ports wouldn't be a problem."

Just a question: How do you lower the port .080 ?

Need data about this set up. Carb size and diameters of the RV cover if possible, thanks a lot for details.

Hard to get data here in Germany, because we have no sleds here like you

Greetings from Germany

Agria Speed Freaks

rototiller racing 670 powered

When I built MY big bore I got the liners from Union Bay it came with with the port modified to use with a stroker crank, I cut the bottom of the jug off to get the deck to match the piston! The problem is this was 20 years ago and Union bay is not in business any more.

 

Too bad we don’t have a source for bolt on stuff for these old motors. Kits, heads, RV covers, pipes.....

 

An ebay seller that says he has several 82 mm / 740 cc LA sleeves and Wiseco pistons:

https://www.ebay.com/itm/skidoo-rotax-670cc-big-bore-sleeves-740cc/143170381827

 

Too bad we don't have a source for bolt on stuff for these old motors. Kits, heads, RV covers, pipes.....

The Crank Shop did have some Billet RV Covers, and did Modify Stock Heads with Dome Inserts. There was a guy in Nebraska who was making a 670 Billet Head Shell, I think you had to still buy the Domes, his Phone Number is on the Head. LA Sleeve had the 670 Big Bore Sleeves, and the Pistons and Sleeves are on eBay often. Aaen & Jaws probably still make a 670 Tuned Pipe. There was a bunch of Union Bay NOS Billet RV Covers on eBay just recently.

The trouble is, not many Sled People are really Racing either New or Old Vintage Sleds today, so there isn't much of a demand or $$$ in it. The Avg Billet Sled Head today is $400, a Billet RV Cover $125. Custom Tuned Pipes can very $450 to $650+. Wiseco will make Custom Pistons Avg $180ea.

A Stock 1993 670 Dynoed 115.7hp@7750rpm! The 617 was around 106hp, the 583 was around 97hp, the 521 was around 85hp. How much HP does the Avg Person really need? My 1994 Yamaha Vmax 600 is 95hp and one of the Heaviest Trail Sleds and it will do 105mph+.

Years ago, the people who bought out Union Bay Racing, I inquired to have a 670 Billet Head made, they wanted $800 to Design & make a one off Billet 670 Head. They said they never got the 670 Head Data from UBR.

Today, you have Free 3D CAD/CAM Software, Small Home Type CNC Mills & Lathes to Design and make about anything you can dream up. There is even Industrial 1st & 2nd Generation used CNC Mills some with Automatic Tool Changers & CNC Lathes out there today real Cheap $1,500+ if you look around. I have seen some as low as $600 that maybe has a Bad Controller, which you can retrofit using a PC and Mach3/4 Software. Most CNC Tools Pay for themselves real quick.

What would a Custom 247/250, 277, 292, 299/300, 318/320, 335/340 Single Billet Head or Free Air Head be worth today?

A Block of 6061 to make a Billet Head off ebay to make one Head Avg $20-$30 depending on Head Size.

 

"When I built MY big bore I got the liners from Union Bay it came with with the port modified to use with a stroker crank, I cut the bottom of the jug off to get the deck to match the piston! The problem is this was 20 years ago and Union bay is not in business any more."

@mydoo,
what kind of stroker crank do you use? The watercraft crank fits plug and play or modify with parts from the stock crank? Where can I get data about the watercraft pistons (dimensions)? Interested in mod a 670 in a torque monster. 7200 rpm with lots of torque would be great for me. Sadly I am 20years late, but let this old stuff live and race
Would be great to get some information, thanks a lot
greetings from the snowless Germany

 

"When I built MY big bore I got the liners from Union Bay it came with with the port modified to use with a stroker crank, I cut the bottom of the jug off to get the deck to match the piston! The problem is this was 20 years ago and Union bay is not in business any more."

@mydoo,
what kind of stroker crank do you use? The watercraft crank fits plug and play or modify with parts from the stock crank? Where can I get data about the watercraft pistons (dimensions)? Interested in mod a 670 in a torque monster. 7200 rpm with lots of torque would be great for me. Sadly I am 20years late, but let this old stuff live and race
Would be great to get some information, thanks a lot
greetings from the snowless Germany

I have never heard of any Stroker Cranks being made for the 670. Stock is (78mm x 70mm) 669.2cc. Big Bores that I have seen made. 670 used 132mm Rods.

(81mm x 70mm) 721.7cc called a 720.

(82mm x 70mm) 739.6cc called a 740.

(82.5mm x 70mm) 748.6cc called a 748.

Seadoo made a 718/720 Stock was (82mm x 68mm) 718.5cc. Used 125mm Rods. Seadoo PTO's are Threaded. I think the 718/720's use a bigger 102-104mm Head (6) bolt pattern. Never got a 718/720 Cylinder to figure it out. With a little effort, I'm sure they could be adapted to fit. I have always wondered if a 650/657/718/720 68mm Stroke Crank would work in a 583/617/670 Case. Could the Threaded PTO still be turned down to either 33mm 1:7.5 or 30mm 1:10 Taper? Hot Rods in Des Moines, IA still make New Seadoo 650/720 68mm Stroke Cranks.

Seadoo also made a 650/657(Non RAVE) Stock was (78mm x 68mm) 650.1cc. Used 125mm Rods. The 650/657 use's the same (6) Bolt Head Bolt pattern as the 670 based off a 100mm Bolt Circle. On the 650/657 Cylinders, two bolt holes line up, and two are offset a little.

Skidoo made a 617 (76mm x 68mm) 617.2cc. The only Big Bore I have seen offered was (79.5mm x 68mm) 675.3cc. Used 125mm Rods.

Same 79.4mm Piston was also used to Big Bore a 580/582/583 Stock (76mm x 64mm) 580.9cc and (79.4mm x 64mm) 634.0cc. Used 125mm Rods.

There was a Big Bore Sleeve made for the 521 (72mm x 64mm) 521.3cc to make it also into a 580. Seadoo also made a 580/587.

My Yellow Seadoo 650/657 Cylinders on a 670 Case. You would also need to plug or Weld up those two little holes on Exhaust Side.

 

Union Bay Billet Heads, Billet Rotary Valve Covers, and other Brands come up on eBay once in while. You could use a Seadoo 650/657 Billet Head with an Inline Thermostat, and a Bolt on Water Neck.

 

Bolt-On Water Necks for using Seadoo Heads.

 

@ Rotax Flyer,

many nice information.

Thought to get an information about the crank that mydoo use. may be possible to use the 787 crank with 74mm stroke in combination with 82mm bore.

Read in another thread about the "800" RV engine vs a 800 series III engine... That sound awesome and more torque in the bottom end.

Thanks for any statements about that

Greetings

Agriaspeedfreak

 

@ Rotax Flyer,

many nice information.

Thought to get an information about the crank that mydoo use. may be possible to use the 787 crank with 74mm stroke in combination with 82mm bore.

Read in another thread about the "800" RV engine vs a 800 series III engine... That sound awesome and more torque in the bottom end.

Thanks for any statements about that

Greetings

Agriaspeedfreak

We tried the 787 sea doo Crank for the skidoo but it is larger main bearings and is not interchangeable with the skidoo Cases. The Crank that was used in our stroked and bored engine was a Custom billet made by Union bay. When that Crank destroyed it self it was replaced by a stock

670 crank. the engine was originally 82 mm bore with 74 mm stroke for 782 cc. When the original crank broke is when I modified the jugs and switched to a stock 670 crank, by cutting the bottom off the jug it lowers the port witch shortens the port timing! The amount I cut off was the distance fron the top of the piston to the top of the bore!

 

@ Rotax Flyer,

many nice information.

Thought to get an information about the crank that mydoo use. may be possible to use the 787 crank with 74mm stroke in combination with 82mm bore.

Read in another thread about the "800" RV engine vs a 800 series III engine... That sound awesome and more torque in the bottom end.

Thanks for any statements about that

Greetings

Agriaspeedfreak

While I have never heard of anyone putting in a 787/800 RV Crank in a 670 Case, just about anything is possible if you have the Time & $$$ to throw at the R&D Machining needed done. Are you sure it's 74mm Stroke and not some oddball, like 74.5mm or 74.9mm? There were a few places that use Off Set Crank Pins or Welded up the Crank and Re-Machine them for a Higher Stroke. I would Think it might be easier to just swap out Engines, 670 for a 787/800. Another Option is to add a Turbo to the 670. You also have a Standard 670 1992-1999 and a 670HO Option 1998-1999. So what does a Stock 670HO actually Dyno?

(78mm x 70mm) 669.2cc, Stock 115.7@7750rpm, for 669cc making 115.7hp = 94% Volumetric Efficiency!

(82.5mm x 70mm) 748.6cc. So 748cc using 94% Volumetric Efficiency at 7750rpm = 128hp!

--------------------------------------------------------------------------------------------------------------

(82.5mm x 74mm) 791.4cc. So 791cc using 94% Volumetric Efficiency at 7750rpm = 136hp!

(82.5mm x 74.5mm) 796.8cc. So 796cc using 94% Volumetric Efficiency at 7750rpm = 137hp!

(82.5mm x 74.9mm) 801.1cc. So 801cc using 94% Volumetric Efficiency at 7750rpm = 137hp!

https://www.mk5cortinaestate.co.uk/calculator3.php

Stock 1993 670 Dynoed & and a 670 with a Turbo using 7 lbs & 11 lbs.