Willard's vintage Hotsaw Builds

[Willard]

Back to work on the YZ125 after the long side track with the CR250R.
Tack brazing aluminum then after off to the tig welder for finishing.

Another few ideas here for grips for the rear handles.

 

[Willard]

No where near cutting the YZ125's top handle uprights to balance yet.
But here's a side profile pic of the 18" bar with a 12T .404 sprocket.

If I keep the high numbers road race porting I'll run this sprocket with .050 50AL .404 chain.
If I lower the porting numbers to drag race porting then I'll run a 14T sprocket.

12T is equal to a 13T 3/8"
14T equal to 15T 3/8".

 

[Willard]

I ran the numbers...it is crazy mild!! 178/119 if you decked it .040 or 1 mm to keep it simple, you would need to lift the transfers .080 or 2 mm to get 128° timing. And the exhaust...you would need to lift the exhaust .200 or 5mm to get 193 and 6mm to get 196!!!

got me thinking....trx piston 3mm shorter, you could cut .020-.040 off the base and 4mm ish of the top and the transfers would be 128-130 and the exhaust would still need to be lifted 2-3mm, crazy! Or she would love a stroker! Lol

Just finished going over my CR250 port measurement notes.
Trouble was I was measuring both cylinders and averaging measurements with the rounded edge of the piston.
This morning I re-measured the 66.75mm cylinder port heights without piston and measurements are same as my original numbers earlier in this thread without the piston.
I don't know where the 1.19mm deck clearance came from when my notes says 1.50mm with both cylinders.
The 68mm cylinder is still 43/59 .

Better numbers now for the 66.75 cylinder.
42mm/58mm. Deck 1.50mm
Like said earlier degree #'s are 182/126.

 

[Willard]

So with the piston, 1.5mm in the hole, your timing would be 182/126 and that would put the transfers even at the bottom of the port, 2mm in the hole 184/128, I am guessing it’s 1.5mm in the hole. If it’s 1.5mm in the hole, I would deck the cylinder 1.5mm lift the transfers 1mm and the exhaust 3mm, that would set you up with 191/130

how thick is your head gasket?

I wouldn’t remove the exhaust bridge, you can and will run fine, rings aren’t an issue, you just can’t make the port as big. No wings, and without sub exhausts, I don’t think it preforms as well.

Like what was said .

 

[Willard]

I couldn't find my crank stand to check crank runout.
So when starting to weld up a new one I discovered the welding magnets worked just fine.

 

[Willard]

It was -46° below this morning and I didn't want to open the window for some clean air in my little 12'×8' shop.
Got rid of the pylon and extra shop vac downdraft table setup.
Built a 2'×2'table out of a 20" box fan with a 20"×20" hepa furnace filter laying on the backside of it.
Takes no time at all to clear out the air while sanding or cutting carbon fibre and the magnesium grade aluminum I'm working with.
Figure out something new every day.

 

[Willard]

Little quick upgrade on the new downdraft table...new legs.

Project is coming along good . Had to put the Cr250r in the bin storage so I could concentrate on the YZ125. Lol.
Taking shape, nothing new to show. Have been doing alot of internal work and R&D.

 

[Willard]

Another major upgrade here for anyone interested in doing a DIY downdraft table.
For $8 I got this reusable washable 20"×25"furnace filter that I cut down to 20"×20". Left over piece in my hand.
Works like a charm with greater suction velocity.

 

[Willard]

Almost had pics today of the progress with the YZ125...almost!

My welder had to order parts for his tig micro torch which came in this morning.
With the very small size and complexity of my fuel tanks with built in bar oil tank it can only be welded together with a small tig micro torch.
Also got the pipe ready for final weld but I'm being Mr Dad today and can't be with the welder to guide him through the job.
Kids got a no school day today. Welding shop is closed tomorrow for the weekend.

 

[Willard]

So with the piston, 1.5mm in the hole, your timing would be 182/126 and that would put the transfers even at the bottom of the port, 2mm in the hole 184/128, I am guessing it’s 1.5mm in the hole. If it’s 1.5mm in the hole, I would deck the cylinder 1.5mm lift the transfers 1mm and the exhaust 3mm, that would set you up with 191/130

So seeing my CR250R piston is 1.5mm in the hole and timing at 182/126.
I'm looking at the complex roof profiles in the transfer ports. Rather then raise the transfer ports 1 mm and the exhaust 3mm, I'm thinking better to raise cylinder 1mm then raise exhaust port 2mm.
Then finish with lowering transfer and exhaust ports floors 1mm and deck 2.5mm off the top of the cylinder.

 

[Bigmac]

So seeing my CR250R piston is 1.5mm in the hole and timing at 182/126.
I'm looking at the complex roof profiles in the transfer ports. Rather then raise the transfer ports 1 mm and the exhaust 3mm, I'm thinking better to raise cylinder 1mm then raise exhaust port 2mm.
Then finish with lowering transfer and exhaust ports floors 1mm and deck 2.5mm off the top of the cylinder.

To do the equivalent of a one mill spacer, you’re basically just doing a three base gasket stack unless you find custom .010 gaskets, I have done the three base gasket set up before, and just Honda bonded the three gaskets together it works well.

 

[Willard]

I haven't measured the thickness of my base gaskets so can't say thickness #'s
A third gasket made out of thin metal glued between 2 base gaskets would offer good strength.
1 mm is only approximately 0.039"

So now I have a baseline for when I get further into the build near completion when time comes for tuning.

 

[Bigmac]

Most Honda gaskets for the base are .18-.020, so three are .054 or .060. Basically .036-.040. For the trx I can get basically any thickness I want, .010, ,015, .018, .020, .025. And .030. I like the metal .010 cometic and .015 coated metal. I am sure cometic could make you a gasket, or even a gasket spacer

 

[Willard]

I really like the rubber coated metal base gaskets Stihl introduced in the mid 1990's. Was a big deal back then.
I got several new complete gasket and top end sets for the '83 CR250. Cometic is one brand and the other is the Italian Apex?? (Have to leave my arm chair and check them out in the shop).
I have found size differences in both brands .
I think a rubber coated stainless steel spacer totalling .060" would be the way to go to help reduce cylinder bore distortion when torquing.

Thanks I'll put that in my notes about getting a hold of Cometic for some custom sizes and spacers.

*edit* Just checked out the Cometic website and their family run business video.Wow what an amazing success story!

 

[Willard]

Been stuck with a bad chest cold for thr last few days. On Monday I went to the clinic to see my doctor about a physical checkup.
What hangs around clinics? Bad viruses.

Now that I have pistons for the CR250 I checked to see if they have a piston pin offset. No offset... zero neutral. The cylinder has zero offset too. Except the head has a bit of side offset. Might be a couple bad studs or torquing might straighten it out.

The YZ125 has 1/8" (3mm) pin offset towards the exhaust. I ran it last year in the reverse rotation and she had no problem whipping past 12K rpm and no vibration.
50mm stroke is pretty short reason they do it. But newer YZ 125s most only have 1mm offset.
Race her at 16:1 fuel mix and shouldn't have to worry about thrust on the exhaust. With less minor thrust will balance out.

So I see BDT is selling on Ebay, some nice beautiful ATC/TRX 250R pipes.
I'm building mine correct from scratch.

Got these 2 Flex Hone brushes in 57mm 240 grit and 67mm 320 grit for both engines
Should clean up the 4 cylinders nicely. May get a 120 or 180 grit for both to do the intial hone and then finish off with the 240 and 320.

 

[Willard]

Bit of good info I learned.
Don't chamfer transfer ports, only remove burs off the transfer port window edges.
Reduces short circuiting.

 

[Bigmac]

Bit of good info I learned.
Don't chamfer transfer ports, only remove burs off the transfer port window edges.
Reduces short circuiting.

I’m not to sure about that, kind depends on your definition of chamfered? Your rings will die if you don’t bevel or chamfer the transfer ports, it may not need to be as much as the exhaust port, but you need to do more than debur, the sharp edge will wipe the oil off the rings and cause scuffing. Can you explain how radiusing the port would cause short circuiting? I can see how a small amount of the charge could get lost for a milasecond, and a small amount of the case compression lost, if the chamfer was extreme it would change the port timing and roof angle, but that would be extreme

 

[Willard]

Thanks, good to get a second opinion!
I don't think there would be a problem of oil getting wiped off the rings at the transfer port side of the cylinder. As long as a good oil retaining plateau valley cross hatch is maintained in the cylinder wall.
The piston being oval shaped with major and minor thrust pressures on the exhaust and intake side, shouldn't put anywhere near as much at the side point of the rings.
By the time the rings get down to the transfer ports compression side thrust on the rings is gone.
Don't forget there's a bridge between the transfer ports also.

I was looking at my YZ125 cylinder which is factory stock standard bore . Radius on exhaust port top bottom edges but transfer's edges are sharp.

 

[CR888]

I think on forums like this chamfering ports gets taken way overboard. You definitely don't want chamfer in the port sides as it encourages the ring to sink into the port thus making them more vulnerable. The top/bottom and be done with a finger and some 320grit. But I suppose feeling the window edges with your finger tell you a lot too. But the deep bevel chamfers you often see people do are poor & unnecessary. Just my thoughts on the issue.

 

[rogue60]

I think on forums like this chamfering ports gets taken way overboard. You definitely don't want chamfer in the port sides as it encourages the ring to sink into the port thus making them more vulnerable. The top/bottom and be done with a finger and some 320grit. But I suppose feeling the window edges with your finger tell you a lot too. But the deep bevel chamfers you often see people do are poor & unnecessary. Just my thoughts on the issue.

Not that I mod 2T engines like the guy's here do but myself I always chamfer the sides of ports.
Why? Sharp side port edges wipe oil off rings in those particular spots with the ring not moving much thanks to the ring locating pin could be a problem down the road I guess...
Must be why I've never seen an OEM 2T cylinder without side port chamfering apart from Chinese made anything is possible then lol...