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Discussion Starter #1
My first post here and I'm very happy to be a part of this great forum!

I'm building a 1983 CR250R 72mm stroke motor and have found it's the next best thing to a TRX motor. Along with it not having a PV it has a 7 stud head, great intake breathing capabilities and a solid crank with no tin can covering.
Stock it has mild 182°/126° porting with the piston 1.5mm in the hole.
My plans are to get it to 191°/130° with 29 blowdown.
But I have a problem. When looking up inside the cylinder I notice the head is off center . Maybe I'm wrong...I have heard some CR250R have offset cylinders.
Its piston pin is not offset.
To properly to cc the head do I need to machine the head dome to center?
Thanks.
Here's a pic.
20200208_133148.jpg
 

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No intentionally offset, some cylinders and heads are slightly off concentrically, simply from machining tolerances stacking up in one direction or another.

CC the head as is, no need to center as you have a flat diameter that will not change CC volume.

Carlos
 

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Discussion Starter #3 (Edited)
Thanks Carlos, that's the answer I wanted to hear!
Pictured above is my 68mm cylinder. My spare 66.75mm cylinder with the same head mounted has the same offset but with much less. So I should get another head for a spare and see if it's any different. Lots of '83 heads on ebay with some in mint condition.
 

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Thanks Carlos, that's the answer I wanted to hear!
Pictured above is my 68mm cylinder. My spare 66.75mm cylinder with the same head mounted has the same offset but with much less. So I should get another head for a spare and see if it's any different. Lots of '83 heads on ebay with some in mint condition.
Yes, many older 250R parts can be found for low $'s...

Love your work on the saw's Willard...good to see some thinking outside the box, innovation, and skill.

Carlos
 

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Discussion Starter #5
Thanks Carlos, I definitely like working on these engines especially the '83 CR250.
I'm sitting on the fence whether or not to get the '83 port numbers up to the level of a 2001 CR250. Back in the day the 1983 CR250 was known for winning holeshots.
I think today putting a PVL ignition, Mikuni SBN carb, Vforce 3 intake and a good cone pipe will work just fine on it especially in smaller logs with the right sprocket gearing .
But the higher port numbers I think may be the only way to go. I got a spare cylinder so testing is in order.
 

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Thanks Carlos, I definitely like working on these engines especially the '83 CR250.
I'm sitting on the fence whether or not to get the '83 port numbers up to the level of a 2001 CR250. Back in the day the 1983 CR250 was known for winning holeshots.
I think today putting a PVL ignition, Mikuni SBN carb, Vforce 3 intake and a good cone pipe will work just fine on it especially in smaller logs with the right sprocket gearing .
But the higher port numbers I think may be the only way to go. I got a spare cylinder so testing is in order.
If you play with 2 strokes long enough, you will learn their are NO real magical porting numbers, generic timing, or secret numbers. Their is 'fine tuning' to each particular build, purpose and matched combinations. In your case, if you want the Baddest Saw specific to your build, physical abilities and style, you will need to do a lot of R&D, testing, and fine tuning.

Carlos
 

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Discussion Starter #7 (Edited)
If you play with 2 strokes long enough, you will learn their are NO real magical porting numbers, generic timing, or secret numbers. Their is 'fine tuning' to each particular build, purpose and matched combinations. In your case, if you want the Baddest Saw specific to your build, physical abilities and style, you will need to do a lot of R&D, testing, and fine tuning.

Carlos
Good advice Carlos, thanks!

What I've seen in the evolution of hotsaws in the last 40 years is Mcculloch kart engine saws.
Italian kart engine saws.
Can Am bikesaws.
ATC/TRX saws.
Rotax PWC engine cut in half (1cylinder removed) making over 325cc displacement and over 10K rpm in the wood.
Latest Wankel kart engines.
Presently what's winning in the Stihl Timbersports is a Honda 330 Sphinx 7 transfer ports and 3 exhaust port engine with only about 8K rpm and tall gearing making it a user friendly powerhouse of a saw.
Lots of guys out there running high revving 60+hp YZ300+cc and many can't handle them and get disqualified from not making complete cuts.
Standard rules are on the word go saws need to be started and make 3 complete cuts within 6 inches of 16-20" diameter log.
Stihl Timbersports has lowered the 20" diameter log over the last few years to 18"-19" which seems to have pulled the reins on the bigger Rotax saws that have dominated for about the last 20 years.

I'm being realistic in my own mind not going to a new big bore Honda. And stay under 270cc with the 1983 Honda cr250 and have some fun. I'm used to a 125 this will be a good learning curve.
 

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Discussion Starter #8 (Edited)
I hope I don't get into trouble for posting this.
This is the new Hotsaw cylinder LED posted on their FB page.
Honda 330 Sphinx cylinder with 7 transfer ports and 3 exhaust ports.

FB_IMG_1582593842806.jpg
 

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Yup, Sphynx, Puma's, Saber's have been around for 7-10 years in the 250R World, and now the new Lynx. All are CP Industries Aluminum Cast, 7/3 Ports, sleeveless cylinders, meaning no steel sleeve. The bore gets Nikasil plated. All these have some of the most modern port layout, very similar to KTM's thinking.

BDT Motorsports has built a lot of Sphynx's (78MM bore), Puma's (85MM Bores) & Saber's (98MM bores), more than any other builder the past 7 years according to CPI. With that said; today in 2020, I don't believe anymore they are that superior to others as they had been in 2014-2018, the New ProX's and ESR cylinders are quite good. The most HP made on the BDT Dyno for a 363-370 (meaning 78MM Bore x 76-77MM stroke) is no longer on a CPI Sphynx...:)

The attached picture is of a recent BDT Motorsports Spynx setup for TT Racing circuit.

Sphynx2.jpg Sphynx1.jpg

Carlos
 

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Discussion Starter #10
Yup, Sphynx, Puma's, Saber's have been around for 7-10 years in the 250R World, and now the new Lynx. All are CP Industries Aluminum Cast, 7/3 Ports, sleeveless cylinders, meaning no steel sleeve. The bore gets Nikasil plated. All these have some of the most modern port layout, very similar to KTM's thinking.

BDT Motorsports has built a lot of Sphynx's (78MM bore), Puma's (85MM Bores) & Saber's (98MM bores), more than any other builder the past 7 years according to CPI. With that said; today in 2020, I don't believe anymore they are that superior to others as they had been in 2014-2018, the New ProX's and ESR cylinders are quite good. The most HP made on the BDT Dyno for a 363-370 (meaning 78MM Bore x 76-77MM stroke) is no longer on a CPI Sphynx...:)

The attached picture is of a recent BDT Motorsports Spynx setup for TT Racing circuit.

View attachment 62119 View attachment 62121

Carlos
That's awesome Carlos!
In a little over a month from now during spring break I'm taking my family to San Francisco for a 10 day holiday.
We'll be taking day trips as far south as the Sequoia national forest.
Now if I can convince my wife and teenage daughters to drive a little further south into Alta Loma I will be a very happy man!!
 

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That's awesome Carlos!
In a little over a month from now during spring break I'm taking my family to San Francisco for a 10 day holiday.
We'll be taking day trips as far south as the Sequoia national forest.
Now if I can convince my wife and teenage daughters to drive a little further south into Alta Loma I will be a very happy man!!
Willard you got an open invitation to visit BDT Motorsports; just let me know ahead of time when you'll be in the Rancho Cucamonga (Alta Loma) area....I guarantee their are NO other 250R shops like BDT, everything & every part to build, fabricate, test,and tune under one roof :)

Carlos
 

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Discussion Starter #12 (Edited)
Willard you got an open invitation to visit BDT Motorsports; just let me know ahead of time when you'll be in the Rancho Cucamonga (Alta Loma) area....I guarantee their are NO other 250R shops like BDT, everything & every part to build, fabricate, test,and tune under one roof :)

Carlos
Carlos, invitation accepted. Thankyou, I've heard A LOT of good things about BDT!

This is our first trip to California so the area is all new to us. I do hear there's as many people in California as there is in all of Canada. Haha.
We're staying right in San Francisco and will be touring all the attractions with our rental car. When we get down to the Sequoia Park it would just be a quick trip on the freeway to NE Los Angeles.
I'll definitely give you lots of warning days before we can stop in.
 

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Carlos, invitation accepted. Thankyou, I've heard A LOT of good things about BDT!

This is our first trip to California so the area is all new to us. I do hear there's as many people in California as there is in all of Canada. Haha.
We're staying right in San Francisco and will be touring all the attractions with our rental car. When we get down to the Sequoia Park it would just be a quick trip on the freeway to NE Los Angeles.
I'll definitely give you lots of warning days before we can stop in.
Perfect....!

Carlos
 

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Carlos, invitation accepted. Thankyou, I've heard A LOT of good things about BDT!

This is our first trip to California so the area is all new to us. I do hear there's as many people in California as there is in all of Canada. Haha.
We're staying right in San Francisco and will be touring all the attractions with our rental car. When we get down to the Sequoia Park it would just be a quick trip on the freeway to NE Los Angeles.
I'll definitely give you lots of warning days before we can stop in.
I just watched the CNN news report this morning about the San Francisco Corona virus state of emergency.
My spring break vacation doesn't look so good!
 

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I just watched the CNN news report this morning about the San Francisco Corona virus state of emergency.
My spring break vacation doesn't look so good!
Yup, not good news, not good for anyone, the country, world or economy...hopefully it's an isolated incidence, or it can be quickly contained...offer to spend time at BDT Motorsports is always open, just keep me posted on your changing plans.

Carlos
 
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