[elime]

I've always used the engine compression divided by the atmospheric air pressure.

I have to admit that is really good! However, that works when all the part are together. If one is putting an engine together and wants to know what the compression ratio will be or is trying to get a certain ratio then one has to measure things.

Is that the Hangtown airport? When I was learning to fly that was one of my stops on my long solo cross country. I remember the runway wasn't flat but had a domed shape and when I took off it was like flying off the edge of a cliff. I think that was the airport.......its been a long time.

 

[Ski Pro 3]

I have to admit that is really good! However, that works when all the part are together. If one is putting an engine together and wants to know what the compression ratio will be or is trying to get a certain ratio then one has to measure things.

Is that the Hangtown airport? When I was learning to fly that was one of my stops on my long solo cross country. I remember the runway wasn't flat but had a domed shape and when I took off it was like flying off the edge of a cliff. I think that was the airport.......its been a long time.

That's the runway for sure! I can see it from the road in front of my house off in the distance. It got real busy this summer during the Caldor Fire.

 

[romtik - The Wide]

Don't neglect to measure the volume of the dome of the piston and the valve reliefs otherwise your calculations will be meaningless -- I am assuming you will be calculating the compression ratio.

yess, thanks for mentioning that. but I already have all the components, so I want to measure just because I like looking at numbers and to give this measurement to the forum.

 

[elime]

yess, thanks for mentioning that. but I already have all the components, so I want to measure just because I like looking at numbers and to give this measurement to the forum.

Piston dome volume and compression ratio are both numbers.

Don't forget compressed head gasket volume and piston deck clearance. Just add in stroke and bore and you will have all the needed info!

 

[romtik - The Wide]

yess, thanks for mentioning that. but I already have all the components, so I want to measure just because I like looking at numbers and to give this measurement to the forum.

As measured the ebay copy of yfm250 cylinder head volume is 25ccm. With that I am starting to fear I will have low comp ratio. Combustion chamver volume 25+3,95+0,2 (head+gasket+ valve reliefs in piston) comes out 29,15ccm and CR with this and 223ccm cylinder around 8.65:1
Am I calculating right? I am assuming zero deck height for the piston
I am surprised at this low CR. What if I went with YFM 71mm cylinder and piston - with the dishing of that piston CR would go even lower below stock yfm 8.7:1 !
I am considering getting the head lowered.

 

[Ski Pro 3]

As measured the ebay copy of yfm250 cylinder head volume is 25ccm. With that I am starting to fear I will have low comp ratio. Combustion chamver volume 25+3,95+0,2 (head+gasket+ valve reliefs in piston) comes out 29,15ccm and CR with this and 223ccm cylinder around 8.65:1
Am I calculating right? I am assuming zero deck height for the piston
I am surprised at this low CR. What if I went with YFM 71mm cylinder and piston - with the dishing of that piston CR would go even lower below stock yfm 8.7:1 !
I am considering getting the head lowered.

Just a reminder, I'm now running a TTR225 engine with a YFM 71mm cylinder and piston off eBay with a stock TTR225 head and getting 145psi dry compression on a warm motor. Wet, it bumps up to 150psi. So if it's true all these heads are the same interchangeable, then you should see the same regardless of what the manual spec says.

My stock 2014 TW200 with 2,000 miles only gets 135psi. Calcs to 9.2:1 CR.

I've checked a couple times now and the TTR225 w/71mm piston is a solid 10psi higher than the stock TW200.

 

[romtik - The Wide]

Just a reminder, I'm now running a TTR225 engine with a YFM 71mm cylinder and piston off eBay with a stock TTR225 head and getting 145psi dry compression on a warm motor. Wet, it bumps up to 150psi. So if it's true all these heads are the same interchangeable, then you should see the same regardless of what the manual spec says.

My stock 2014 TW200 with 2,000 miles only gets 135psi. Calcs to 9.2:1 CR.

I've checked a couple times now and the TTR225 w/71mm piston is a solid 10psi higher than the stock TW200.

I know. you have a complete opposite of what I have I think I'll just wait and assemble it as it is and measure compression then. My friend has OE used xt225 2007 cylinder head, I want to measure it too and compare. Basically I want to compare everything thst is comparable

 

[elime]

Measure the head volume, the compressed head gasket volume, the piston dome volume, the deck clearance volume (if piston is above or below the cylinder) and the sweep volume. Divide maximum volume by minimum volume and get the compression ratio.

When I use a compression gauge it sometimes reads high and sometimes reads low. The gauge is consistent on the day I use it but doing a compression test the next day or a week later the results are different. And I have tried different gauges with the same results. Go figure.

 

[romtik - The Wide]

As measured the ebay copy of yfm250 cylinder head volume is 25ccm. With that I am starting to fear I will have low comp ratio. Combustion chamver volume 25+3,95+0,2 (head+gasket+ valve reliefs in piston) comes out 29,15ccm and CR with this and 223ccm cylinder around 8.65:1
Am I calculating right? I am assuming zero deck height for the piston

Measure the head volume, the compressed head gasket volume, the piston dome volume, the deck clearance volume (if piston is above or below the cylinder) and the sweep volume. Divide maximum volume by minimum volume and get the compression ratio.

When I use a compression gauge it sometimes reads high and sometimes reads low. The gauge is consistent on the day I use it but doing a compression test the next day or a week later the results are different. And I have tried different gauges with the same results. Go figure.

well, yeah, I did that. My piston is flat, it does only have valve reliefs in it. I cannot do much more at this time, since my TW is still running and will be running all next riding season. And whatever I calculate is just to satisfy my numbering need, I won't( don't want to spend more money) on different piston now, because I already have one.
Thanks for your input and I have a question I would think you know the answer to. Do you or anybody know the stock deck clearance for TW200 or XT/TTR225? does either of these engines have zero deck clearance?
If I calculate the height of connecting rod small end from center of crank for tw200 (55,7/2 + 101,5 = 129,35mm) and for xt225 ( 58/2+100,5 = 129,5) there is 0,15mm difference. are the pistons different in height?

how much did the compression tests vary?

And are there available differetn thicknesses of head gaskets for 225 engines??

 

[elime]

The connecting rods are different. The longer stroke has a shorter rod. The short stroke has the longer rod. That way the piston is at the same height and you can use the same cylinder for both cranks.

Deck clearance is zero if I remember right. However, you can increase it by using two or three base gaskets.

The head gasket has three layers. I have never tried it but I have heard other people have removed one layer of the gasket to make it thinner and increase the compression ratio. Or Cometic (I think) makes copper head gaskets in different thicknesses. Nice thing is they are reusable though I reuse the ones that are on there now.

I don't remember how much the compression tests varied. If the sun comes out today maybe I will do a compression test on a TW and see what happens.

 

[romtik - The Wide]

joke at last. My TW won't be an ordinary "six speed". It will be "sick speed" !

XTNG carb - the lectron carb copy- will be reality, it's getting turned down for fitment into intake boot. Airbox to carb boot will be probably 3D printed.

Unfortunately lathe is not the best option, since (as the seller said) most of new carbs don't have concentric flanges.

 

[TWBigBlake]

joke at last. My TW won't be an ordinary "six speed". It will be "sick speed" !

XTNG carb - the lectron carb copy- will be reality, it's getting turned down for fitment into intake boot. Airbox to carb boot will be probably 3D printed.

View attachment 232520

Unfortunately lathe is not the best option, since (as the seller said) most of new carbs don't have concentric flanges.

I was looking into those lectron carbs earlier this year, it'll be good to hear how it performs. Have you used that type of carb before?

 

[romtik - The Wide]

I was looking into those lectron carbs earlier this year, it'll be good to hear how it performs. Have you used that type of carb before?

Nope, that will be my first of this type. I hope what everyone says is true. This one was tuned/bought for ttr225 so it should be almost spot on.

 

[romtik - The Wide]

starting to do some head/port work.

quite crude conditions at my apartment I tried a cutter bit I found in trash at work and it works fairly well.
first up - deshrouding of valves:
before:

almost finished, since I ran out of battery:

next up: getting a dremel tool and cutting bits
I'll measure head volume after I am finished.

 

[reddave]

Every man NEEDS a Dremel! You'll wonder how you ever lived without one, Brother!

 

[romtik - The Wide]

That is true!

Every man NEEDS a Dremel! You'll wonder how you ever lived without one, Brother!

That is true!
We have small one at work and my friend has one, so that'll do.
Until now I never worked on anything right at home. That drill is my first ever personal drill and I got it just few weeks ago

 

[romtik - The Wide]

another idea popped up. adjustable cam timing. main advantage would be no need to remove the gear to spin it to another keyway ground at different angle.

The small 4mm pin that holds camshaft and cam gear spinning together, now with small cam lobe.

machining it shouldn't be that complicated, marking those degrees would be quite challenging (the marks are 1,3mm long. it is a really small part) but I have no idea (yet) how to make it so it won't turn on itself when the engine is running.
Does anybody have a clue?

For the deshrouding of valves mentioned earlier, I made a 6mm ball on a stick to better visualize / find where to grind.

 

[oldworld 124]

I'm right now doing the duration, separation lobe, valve lifts, & other specs on the yfm250 cam, xt225 cam, & a slightly more aggressive xt225 cam. Using a degree wheel and marking stats from .50 up to .63 on the wheel. The reason am noting lots of different settings is because of making the adjusment for the rocker arm valves to cam ratios. Will have the stats on a spreadsheet after I get a cam that has the manufacturer's stats already done. Will be about a month before getting that cam and putting it in a head to get the true base calcs for the others.

Will also do the cam specs for the TW200 when I do the xt225 swap and have the covers off before taking it off the bike.

 

[oldworld 124]

another idea popped up. adjustable cam timing. main advantage would be no need to remove the gear to spin it to another keyway ground at different angle.
View attachment 233428
The small 4mm pin that holds camshaft and cam gear spinning together, now with small cam lobe.

View attachment 233429 View attachment 233430

machining it shouldn't be that complicated, marking those degrees would be quite challenging (the marks are 1,3mm long. it is a really small part) but I have no idea (yet) how to make it so it won't turn on itself when the engine is running.
Does anybody have a clue?

For the deshrouding of valves mentioned earlier, I made a 6mm ball on a stick to better visualize / find where to grind.
View attachment 233431

Might be easier to take out the crankshaft assembly and have the key way milled wider and make a key that is milled offset to the amount of timing desired.
I included a couple of drawings showing how it can be done. Might also be able to mill the slot on the indide of the pulsor instead of removing the crankshaft, but I think altering the crankshaft woud be the best way to do this if playing with the key.
Making a variety of keys would allow one to advance or retard the timing easily.

 

[romtik - The Wide]

I'm right now doing the duration, separation lobe, valve lifts, & other specs on the yfm250 cam, xt225 cam, & a slightly more aggressive xt225 cam. Using a degree wheel and marking stats from .050 up to .063 on the wheel. The reason am noting lots of different settings is because of making the adjusment for the rocker arm valves to cam ratios. Will have the stats on a spreadsheet after I get a cam that has the manufacturer's stats already done. Will be about a month before getting that cam and putting it in a head to get the true base calcs for the others.

Will also do the cam specs for the TW200 when I do the xt225 swap and have the covers off before taking it off the bike.

I degreed yfm250 clone, xt225 and tw125 cams. let's combine our numbers to form bigger database?
here's the file - on microsoft office online. Does this link work?

I am not entirely sure I understand what you're doing, are you talking about rocker arm ratio?