Photos: 2009 Dragon 800CFI engine rebuild, showing bottom end problem

I've attached a few photos of a 800 CFI Dragon Motor that had been Turboed all last year. This motor has over 3000 miles with boost levels from 10 - 13+ lbs.

Everything looked very nice and better then I expected........Except the crankcase.

The weak link of the new motor is shown in the photos.

The cracked area is the snap ring groove on the mag end of the center bearing saddles.

800 Dragon

Don't Panic, This is completely repairable.

I did three of these last year.

If you notice the lock-ring groove was machined into the crankcase a little too close to the outside edge of the inner MAG wheel area.

The part you see that's cracked will be completely machined out so it does not fracture and fall into the motor at a later time.

Then a new lock-ring will be machined into the PTO bearing saddles, this area is much stronger.

** NOTE ** I checked the run-out on this Turbo crank and after 3500 hard miles it was within .001 on the PTO-side, and .003 on the MAG-side.

The PTO bearings will be upgraded and will include the snap ring.

In order for the Snap ring lands to get cracked out like this, the forces from the Clutch slamming into the belt have to transfer thru the PTO, into the PTO connecting rod pin and into thru the center section and onto this snap ring.

I still cannot understand why Polaris relocates this snap ring so far AWAY from clutch. This also illustrates why belt to clutch side clearance in the primary and keeping your clutches in tune are so critical. As the primary slams against the belt with too much clearance, it acts as a "slide hammer" and can wreck havoc on the crank.

This was awesome to see. The 800 CFI Crank is built very well.

I've attached a few photos of the run-out.

break down.

I know I trashed the new CFI 800 when I looked at a break down of the motor.

There has been countless theroy's on the weakness of 2000/2005 Polaris 800 Big Block cranks.

Many thoughts were that the old 800 crank had harmonic problems ( Not true ).

Both motors have the same Bore & Stroke - 85mm X 70mm

Design weakness in the old 00/05 crankshaft I have mentioned before.

#1 - No bearing lock ring on the PTO-side
#2 - the 14mm hole bored into the PTO end to harness the clutch puller,
and hold the clutch bolt is ( to big in diameter, and is bored to deep )
#3 - The lower connecting rod pins were to small 27mm and could not support the slide hammer effects from the drive clutch.

00/2005 800 BB Crankcase problems.

#1 - inconsistant bearing area sizing.
#2 - No PTO Lock ring area.
#3 - cylinder stubs passing thru case.

My views on the new 800 CFI crankshaft.

First let me give you some Polaris crankshaft info from years past.

The following numbers refer to connecting rod lower pin diameters.

1997 / 2004 700 ------ 28mm ( Hollow pin )
2000 / 2005 800 ------ 27mm ( Solid pin )
2005 / 2006 755/900 - 30mm ( Hollow pin )
2008 / 2010 800 ------29mm ( Solid pin )

Notice a few things about the lower rod pin diameters.

The 1997 thru 2004 700 had a 28mm hollow pin, and the 2000 thru 2005
800 had a smaller 27mm solid pin. ( a 28mm hollow is just a little bit stronger then a 27mm solid ) But the smaller pin of the old 800 offers less wheel support then the old 700. This is why the old 800 go out of tru and then over load the PTO-end........More 800 pto-end failure was sure to follow.

Then there is the 2005 thru 2006 755/866 Big Blocks that had a 30mm hollow pin, very suitable strength for the 755 bottom-end......But the 866's increased bottom-end torque and lack of PTO lock ring groove over time takes its tole the PTO-end goes out of tru and PTO-end failure soon follows. ( I have never seen a 755 PTO-end failure ) Not saying its never happened.

Now on to the 2008 thru 2010 800 Small Block.

First.......and most important, The 29mm Lower connecting rod pin is the single best thing Polaris did to the 800 CFI.

Is it not true that most people think the OLD Small-Blocks are great tuff motors ???

well.......The old 1999 VES 440 had a 28mm Lower rod pin, Same size as the 1997/2004 700 except ( it was Solid ) even a little stronger then the 700 BB.

So from 1999 & newer 440,500,600 Small Block and the 1997 and newer 700 big block all had 28mm lower rod pins.

Then in 2000 Polaris built the 800 Big Block with a 27mm lower rod pin, And thats where the problems started.

You can go back in time and search the net for Big Bore Small Blocks and
you will never see the crank problems with the 28mm SM like you do with the 27mm BB motors.

There is a fine line between the torque applied and rod pin diameter if there is not a PTO lock ring bearing.

the 755 is a prime example......The torque of a 755 on a 30mm rod pin is little to no-problem, ad another 111cc's and the increased torque at low-end the pto crank wheel goes out of tru over time and then the whipping effect of the drive clutch breaks the crank.

Now that all being said........The new Dragon has a 29mm lower rod pin which should be big enough to support the slide hammer effect of an 800 for a much longer period of time then the old 800 BB. A new 800 is at the end of its game as far as bore go. The new motor stuggles to get to 860 where the old motor can go to 990 no-problem.

The fact remains, The New motor should have had a PTO-lock ring. NOT
an inner MAG-Side to close to the edge of the case groove.

The 800 SB is almost an exact carbon copy of the 2005 /2006 - 755/866, Other then the crank is balanced much better. ** Note ** The New 800 SB crankshaft weighs exactly 3.1 pounds less then the 900 crankshaft.

As far as the bottom ends go, the only difference is the water pump shaft is in the bottom of the SB case instead of the top of the 900 case and they moved the lock ring groove from the inner PTO bearing on the 900 to the inner MAG side on the 800 SB ( and when they moved it ) they inverted it from the inner side towards center to the outter side towards the wheel and made it to thin.

As for the top-end of the new motor.......My feelings are exactly what I said before........Single ring pistons are stupid, the exhaust valve is to wide, the compression ratio is to high. there is not enough water moving around the exhaust port. ( In the mountains non of this matters. ) The flatlanders with poor fuel are the ones that have to worry.

The fact that this motor is a Turbo lends well to the crank PTO-end staying straight..The Turbo kills bottom-end torque at the moment of engagement where the drive clutch moveable hits the belt making it very gental on the PTO-end. HP has never caused much problems to the Polaris domestic PTO-ends.........Its been Hi-Torque and poorly shimmed drive clutches where the clutch is slapping the belt instead of squeezing it.

My conclusion of all this..........

After Updates - I like the new Motor as far as design goes within its 800cc size, Once its got the right Map ( The tree huggers make this almost impossible ) and compression ratio to match the sh!t fuel of today its a pretty good little motor.

28mm Rod Pin - A+

Inner Mag bearing lock ring groove D- ( should have been on the Outter PTO-side. )

Things to come - Twin ring pistons & New Head A+

So as a few have mentioned I have changed my mind about the crankshaft, ( Something I didn't catch in the first break down ) The 28mm Pin is a HUGE improvement even without having a PTO lock ring. I know it doesn't sound like much but 2mm on the O.D. of the pin is a huge strength improvement as far as to help keep the crank straight.

The really nice part about the new motor !!!!! At a later Date when the old Big Blocks are completely woren out the Crank wheels can be ground to except the New Dragon Rods and that will make the olds cranks better then new again.

Long Crankshaft life depends strongly on Rod Pin support ( Via Rod pin diameter and PTO Lock rings ) in keeping the crank tru so the drive clutch does not become its worst enemy.

Dan

EricW said:

Great info Dan.....Hope all is well with ya. i have never soon this case apart, could you fish a Snap-On bore scope through any of the ports to get a look at this area without disassembly? Maybe with the 90* angle lens?

Have a good one and thanks again. EW

Click to expand...

Eric, Its possible to see the edge of the lower half of the case starting to break........If you pull the mag-side reed cage and sneek a 90* bore scope
above the inner crank wheel and point it down between the wheel and case you should be able to see if its starting to break right by the parting line of the upper & lower halves in the front.

I will attach a picture of a broken one.