Big Bore myths DEBUNKED

Stock bore from Skidoo says it's 82mm. I came up with 81.84 mm measuring quickly.


Distance between bolt holes and cylinder wall. 7.93mm


Distance from o-ring to cylinder wall. 3.4 mm


Measured an old Piston off the shelf too from wrist pin to wrist pin. 81.28


Engine displacement equation is

Displacement = (Pi/4)(Bore^2)(Stroke)

800R stoke from Skidoo at 75.7 mm

Pi = 3.1416

(Pi/4) = .7854

(.7854)(82^2 mm)(75.7mm) = 399773.9407 cmm = 399.7739407 cc per stock cylinder just to show it works

Re-writing the displacement equation to find the bore.

Bore = Square Root of ((Displacement)/((.7854)(Stroke)))

Taking the 872

872/2 = 436 cc = 436000 cmm

Bore = Square Root of ((436000)/((.7854)(75.7))) = 85.63471495

Bore of the 872 is 85.6 mm

Taking the 880

880/2 = 440 cc = 440000 cmm

Bore = Square Root of ((440000)/((.7854)(75.7))) = 86.02663789

Bore of the 880 is 86 mm


872R

85.6mm - 82 mm = 3.6 mm

3.6 / 2 = 1.8 mm larger from center of piston all the way around

880R

86mm - 82mm = 4mm

4 / 2 = 2 mm larger from center of piston all the way around

Also have to take into consideration the bolt threads themselves. Not sure the crest to trough on the bolts themselves.[/QUOTE]

BIG JOHN said:

A) This piston is designed to run at .045"-.005" clearances

Click to expand...

You mean .0045", correct?

I have a tonne of respect for BIG JOHN for doing this. I think its awesome that you are willing to stick your neck out and call a spade a spade. I think Dave should come on here and defend the comments that he has on his web page or take them down. Its not "airing dirty laundry".......its getting chit settled.

deaner said:

I have a tonne of respect for BIG JOHN for doing this. I think its awesome that you are willing to stick your neck out and call a spade a spade. I think Dave should come on here and defend the comments that he has on his web page or take them down. Its not "airing dirty laundry".......its getting chit settled.

Click to expand...

Well, Dave doesn't do that... he said so himself on here a week or so ago!:face-icon-small-win

Glad to see this, IMO one of the big things I look for in a big bore is a stock piston I can get elsewhere if by some chance the builder is out of business or charging three arms & four legs for them.

Also, the fact that there are HUGE quantities of Suzuki pistons running around makes that kit very appealing to me. I decided to stop buying proprietary pistons a while ago... I like to change pistons often so both are big factors for me.


I know this isn't the case for both kits, but I like having the option to run that piston.

Few more quick things.....

The material left between between the stock o-ring groove in the cylinders and the edge of the cylinder wall is

872 cc

3.4 mm - 1.8 mm = 1.6 mm

872 cc = 1.6 mm

880 cc

3.4 mm - 2 mm = 1.4 mm

880 cc = 1.4 mm

The material left between the trough of the head bolts to the edge of the cylinder wall is

872 cc

7.93 mm - 1.8 mm = 6.13 mm

872 cc = 6.13 mm

880 cc

7.93 mm - 2 mm = 5.93 mm

880 cc = 5.93 mm

Questions....

1. Why do you weld the o-ring grooves and mill new ones into the head if the stock ones would fit without any trouble?

2. Are the o-rings you include in your kit thicker than stock?

Here is the measurement for the cylinder skirts.



Cylinder skirt thickness

872 cc

5.2 mm - 1.8 mm = 3.4 mm

872 cc = 3.4 mm

880 cc

5.2 mm - 2 mm = 3.2 mm

880 cc = 3.2 mm

Questions....

1. It looks like the thickness from the skirt gets thicker from the skirt to the top of the cylinder. Have you bored an 800r engine past 880? If so why did you not want to release it? I have seen Snow X has done a few 925's.

Visi said:

Few more quick things.....

The material left between between the stock o-ring groove in the cylinders and the edge of the cylinder wall is

872 cc

3.4 mm - 1.8 mm = 1.6 mm

872 cc = 1.6 mm

880 cc

3.4 mm - 2 mm = 1.4 mm

880 cc = 1.4 mm

The material left between the trough of the head bolts to the edge of the cylinder wall is

872 cc

7.93 mm - 1.8 mm = 6.13 mm

872 cc = 6.13 mm

880 cc

7.93 mm - 2 mm = 5.93 mm

880 cc = 5.93 mm

Questions....

1. Why do you weld the o-ring grooves and mill new ones into the head if the stock ones would fit without any trouble?

2. Are the o-rings you include in your kit thicker than stock?

Here is the measurement for the cylinder skirts.



Cylinder skirt thickness

872 cc

5.2 mm - 1.8 mm = 3.4 mm

872 cc = 3.4 mm

880 cc

5.2 mm - 2 mm = 3.2 mm

880 cc = 1.4 mm

Questions....

1. It looks like the thickness from the skirt gets thicker from the skirt to the top of the cylinder. Have you bored an 800r engine past 880? If so why did you not want to release it? I have seen Snow X has done a few 925's.

Click to expand...

Hey Mike , You ever ride above Shaver Lake area? we should run your sled with my 880 for good fun?

BIG JOHN said:

MYTH #1... The 860 (800 cat) piston skirts are too thin...

A) This piston is designed to run at .0045"-.005" clearances...if you install them at .006" or bigger (like most do) they will fail early...SHR sets them at the proper .005"...record SHR860 mileage is OVER 5000 miles on the same pistons.

Click to expand...

[QUOTE=BIG JOHN;2843096]hmmm

I would need JVB's name (a pm is OK) to verify story/timeline/problems...I also never said "faulty pistons", yes I have moved from cast/cat factory pistons due to some skirt failures , best yet is over 5000 miles on a 860 kit...the new Hyperdrive piston has had 1 failure in 2 seasons...pretty happy about that...as for having a motor for 3 months? (need cust. name to verifty this and why- I keep detailed notes on all BB motors)...not answering phone? (sorry, that doesnt happen here)...warranty? (I warranty MY work, not the customers or choice of fuels etc.)..its a MOD...no wty is expressed/implied...

In closing...I spend ALOT of time/money making MY customers happy...I offer the best of products/service possible...but the old saying still applies..."you cant please ALL the people ALL of the time"...:face-icon-small-win-BJ[/QUOTE]

BIG JOHN said:

MYTH #2... The 880 bore is too big and the cylinder walls are paper thin...

Lets start with a little math...

what is 1 mm in thousandths? .040"

what is half of 1 mm? .020"

what would the cylinder wall need to be bored to change bore diameter .020"? .010"

A) a .010" thinner wall thickness DOES NOT make it ANY less reliable...period.

I have cracked a cylinder wall on an 880 and I know of a few others that have had similar issues. In structural engineering minute tolerance's are the diffrence between success and utter failure. Some people do not like living on that edge.



MYTH #3...you cant weld the aluminum SKI-DOO cylinder due to some coating???

A) this is easy...PROVE IT!! ...while we are at it, I have some SLICK 50 for sale.


What coating are you referring to? Are you referring to heat treating? Heat treating is a process and not a coating, you build motors you should know this. Do you want it proven that welding a heat treated product weakens it? Is it a concern to you with your cylinders? Maybe not but it is to others.

Remember, what is right for one is not right for all. Not saying one or the other is right way, but different standards is what gives the world variety.



This post is for your information...ALOT of DIS information out there...BJ


Myth Number #4 A Etec cannot be big bored or modified without a stand alone fuel box.




BTW, SHR can/will/does FIX all brands of BBs out there...just saying.



check out my new website!!

Click to expand...

First off it can only be a myth if it is not proven? Am I correct? If we touch the Loch Ness monster even once and could verify it, Is it a myth or a fact?


I would say much of what you are calling a "myth" Bj have been proven issues. What failure rate makes them okay for some people have different standards ?


I have had an 880 and it ran well, I have had a 880 cylinder develop a hairline crack on me too. I know of a couple of other guys with different engine builders that have had a similar issue. Is it wide spread? No, But it has and does happen. We tried a lot of diffrent things with our 880 in the beginning and finding a piston was one of them. Many things were learned after a few sets of pistons. You're welcome what we learned I am sure helped everyone in the 880 world.


I have had a lot of fast sleds that worked very,very well in the mountains here in Colorado. Are my sleds the best for every Tom,Dick and Harry out there? No, but my sleds are ran hard and run well. To put it bluntly I have a put up or shut up attitude when it comes to sleds... and there have been a lot of quiet people around me. At the drag races to the mountains our sleds have performed well. I have successfully ridden in the backcounty sleds that have won Open mod titles in RMSHA, that went on to spending a few years being ridden hard by me in the back county and where did it go to be put out to pasture? Was the sled toast? NO, It went back east where it won Hill drag title after Hill drag title.


All of my nasty, hard running backcountry sleds have had one engine builder.... Dave Trygstad. I learned about Dave in the pages of Snow Week and when sled racing was bigger from drag racing to cross country.
Back before the internet was cool..



You can call me a Trygstad Cheerleader..... You can bet your a$$ I am. He has my full respect.


What it is that I learned to respect about Dave is his commitment to quality, to bringing the best possible product to the table in his eye's. I have never been stranded by a Trygstad engine and I have run 8900 RPM 800's in the backcountry to wicked big bores. It is this commitment that brings me back to his builds time and time again.


My point here is if you are okay with thickness of the walls on your 880's or the how welding on heat treated cylinders affects the temper. Then they have met your testing standards.


That does not mean they have met everybodys standard's! Its why we have Ford and Chevy.


Not everyone would like my personal sleds, but everyone will like Dave's commitment to bringing a quality product to the customer.

If you like BJ's stuff use it he is a good guy and builds good products, but dont call another persons results from their testing "Myths" they may actually be true.

Dbook said:

[QUOTE=BIG JOHN;2843096]hmmm

I would need JVB's name (a pm is OK) to verify story/timeline/problems...I also never said "faulty pistons", yes I have moved from cast/cat factory pistons due to some skirt failures , best yet is over 5000 miles on a 860 kit...the new Hyperdrive piston has had 1 failure in 2 seasons...pretty happy about that...as for having a motor for 3 months? (need cust. name to verifty this and why- I keep detailed notes on all BB motors)...not answering phone? (sorry, that doesnt happen here)...warranty? (I warranty MY work, not the customers or choice of fuels etc.)..its a MOD...no wty is expressed/implied...

In closing...I spend ALOT of time/money making MY customers happy...I offer the best of products/service possible...but the old saying still applies..."you cant please ALL the people ALL of the time"...:face-icon-small-win-BJ

Click to expand...

First off it can only be a myth if it is not proven? Am I correct? If we touch the Loch Ness monster even once and could verify it, Is it a myth or a fact?


I would say much of what you are calling a "myth" Bj have been proven issues. What failure rate makes them okay for some people have different standards ?


I have had an 880 and it ran well, I have had a 880 cylinder develop a hairline crack on me too. I know of a couple of other guys with diffrent engine builders that have had a similar issue. Is it wide spread? No, But it has and does happen. We tried a lot of diffrent things with our 880 in the beginning and finding a piston was one of them. Many things where learned after a few sets of pistons. You're welcome what we learned I am sure helped everyone in the 880 world.


I have had a lot of fast sleds that worked very,very well in the mountains here in Colorado. Are my sleds the best for every Tom,Dick and Harry out there? No, but my sleds are ran hard and run well. To put it bluntly I have a put up or shut up attitude when it comes to sleds... and there have been a lot of quiet people around me. At the drag races to the mountains our sleds have performed well. I have successfully ridden in the backcounty sleds that have won Open mod titles in RMSHA, that went on to spending a few years being ridden hard by me in the back county and where did it go to be put out to pasture? Was the sled toast? NO, It went back east where it won Hill drag title after Hill drag title.


All of my nasty, hard running backcountry sleds have had one engine builder.... Dave Trygstad. I learned about Dave in the pages of Snow Week and when sled racing was bigger from drag racing to cross country.
Back before the internet was cool..



You can call me a Trygstad Cheerleader..... You can bet your a$$ I am. He has my full respect.


What it is that I learned to respect about Dave is his commitment to quality, to bringing the best possible product to the table in his eye's. I have never been stranded by a Trygstad engine and I have run 8900 RPM 800's in the backcountry to wicked big bores. It is this commitment that brings me back to his builds time and time again.


My point here is if you are okay with thickness of the walls on your 880's or the how welding on heat treated cylinders affects the temper. Then they have met your testing standards.


That does not mean they have met everybodys standard's! Its why we have Ford and Chevy.


Not everyone would like my personal sleds, but everyone will like Dave's commitment to bringing a quality product to the customer.

If you like BJ's stuff use it he is a good guy and builds good products, but dont call another persons results from their testing "Myths" they may actually be true.[/QUOTE]

Your cracked 880 cylinder, who supplied that cylinder to you. Curious?

It was a brand new Rotax cylinder, brand new motor in fact.

byeatts said:

Hey Mike , You ever ride above Shaver Lake area? we should run your sled with my 880 for good fun?

Click to expand...

I have not gotten down to Shaver Lake area yet. I do have a trail ported Trygstad engine with a head on it. For a trail sled it runs good. The last picture I posted is a buddies 800r that has been scuffed that he let me have last season when his engine went. Keeping it around for the next build. I would love to run against your 880 and 3" track with my turbo. I am curious about the 3" track too. I'll PM you.

BIG JOHN said:

Deaner, thank you...and if you knew me...I am being very NICE as in, I am playing nice in the SW sand box...the funny thing is, aww nevermind...the pot plenty stirred...cheers BJ :face-icon-small-coo

Click to expand...

Reading these posts have allowed me to form my own assumptions too...My gut says 860/880 sales must be slow.. based on all posts here lately. Facts are..the 872 packages appear to be plentiful and bulletproof, I have yet to hear of a failure or unhappy customer on this site. So let the cards lay...

Instead of wasting time worrying about TMS, SHR better focus on what he's good at,, taking care of his customers..because that 872 pkg is outselling and dominating the market by a wide margin from what I can see.

I'm sure there are plenty of facts and numbers to support my assumptions too. :argue:

Both seem to make really good stuff, competition will only make it better. Good job John and Dave.

Still questions not answered. Why not make a 888-890 then if you feel it's safe?

Once again, I know. Thanks.