low end problems with head?

[themountain]

It states that I can use the stock springs with that cam, but would it hurt if I add in stiffer springs which I bought for the z40?QUOTE]

I got stiffer ones with that cam and its fine

 

[Cactus Jack]

well today I was going to measure the stock piston to wall clearences, but the problem is that my stock cam is toast, there has been galling on the actual cam lobes, since it was starved of oil, so I dont think it will be able to open the valves to the full potential. Someone told me it has to be around
.070, so I will measure the piston to wall clearence with the toased cam and see what I come up with that way.

Man , you've run the engine without jumping the 140's oil cooler take off ports ..... DON'T make the same mistake with the new head and cam ......

 

[damann33]

ohh I know man, I have the oil cooler all ready to hook up to the case of the engine.

 

[Cactus Jack]

as I said no suitable pistons + cam chain problems. But wait theres more....now that your grasping these issues try this. Now if you find the workable deck height and gasket thickness you will be forced without further modifications to live with the static compression ratio this gives. BUT you now add cam of choice. Your choice has already been made and that is a z40 profile cam. This cam I have doctored and can tell you that it gets its top end performance by not only increased duration but also its centrelines and the amount of retard it runs. This cam has one of the latest intake valve closing times of all commonly available cams. This cam has the inlet valve still open 1mm at 53.6 degrees ABDC (after bottom dead centre) and actually doesn't fully close until a little past 80 degrees ABDC. As therefore compression does not begin until the piston is fairly well on its way up the stroke your actual running compression ratio (dynamic) is dramaticly lowered. So even if you acheive stock compression ratio with one of these pistons your running ratio with THAT cam may end up 6-1 or something crap like that. You may be better running a stock cam!

...infact I just ran some numbers and estimate you will be around 6.3 to 1 running that cam if you only acheive 10 to 1 static compression. Thats only 148psi cranking pressure. In order to run about 8 to 1 or 210psi crank pressure with that cam, you would need to build the engine with a 13 to 1 static ratio. To acheive 8.7 to 1 running and 230psi you will need 14-1 static...

LOL ....... I had typed out the info below as part of the post advising him to go with the highest dome piston with the highest compression to work better with the cam he has but decided it was probably over the top for him to grasp ..... so I saved it and sent it to myself in an email for future use ..... Macks info above says the same thing but in far greater detail ...

low end problems with head?
‏
From: Cactus Jack ([email protected])
Sent: Friday, 15 February 2008 12:58:58 AM
To: [email protected]

plus you'll have to carefully set up your timing advance curve to suit which most likely requires a digitally mapped ignition such as a Tokyo mods ignition , PVL digital etc ...... probably not too many people do all that with their engines .....

But remember that with your cam you'll lose some of your dynamic compression at lower engine speeds so you need to increase the static (built-in) compression just to get it equal to that of a stock cam ...... as the engine revs there's increasingly less time for the compression to escape ..... so you'll get a good surge as the engine "comes on the cam" and cylinder pressure rises above stock levels .....

With low compression your engine would run lazy and take longer to rev out so you'd be disappointed with the cam ........

If you're not familiar with degreeing cams (indexing) and slotting timing sprocket bolt holes , then I'd stick to the stock cylinder deck height , cam chain length and tension .......

There's a VERY good reason why the chinese went to 28 T cam / 14 T crank sprockets on the 140's ...... while the 120/125/127/138's have 32 T cam / 16 T crank sprockets .... and that means the PCD that the chain runs on was altered to get the chain tension right with the lower cylinder and shorter stroke length ....

 

[damann33]

tru, well I wont be lowering the cylinder that much to effect anything, .3mm lower. I think I will also continue on selling my z40 cam to get a cam without as much duration so that I can have some more compression, because I wont have enough static compression to run it. I think that with the cylinder a bit lower, big dome piston notched out for valves, 28/24 valve head I will be set. Its better then going out and buying a 57mm cylinder, and getting a piston with a 3.5mm dome, he doesnt have any other pistons as well (not in stock). I also want to measure out my stock piston to valve clearences right now, but I dont think it will be an accurate measure since the stock cam is worn out.

 

[Cactus Jack]

Yes it sounds pointless bothering to check the stock valve to piston clearance if the peaks have been knocked off the lobes .... you'll get a false reading anyway ... Are the lobes , rockers , or bearings blued ?????? If so they're RS .... you CAN send the stock cam to get it welded and reground but it'll cost more than the AHP 140 race cam ....

If you weren't in Canada I'd buy the TB cam off you ..... the shipping costs too much and takes too long ......

 

[damann33]

hey man, the they dont seem to be blued they didint heat up that much, there is just some galling, metal to metal contact. I thnk my best bet is to get the ahp 140cc cam, also I can have the z40 cam sold for 45 shipped and insured to you, shipping wont be to much and should take 10 days post. I guess there is no point of measuring I herd .040 is the minimum, so ill aim for something like .060 with the ahp cam.

 

[Cactus Jack]

Check out these dyno charts and specs ....... the specs shown are interesting because they show that the short stroke engine with relatively low compression made more power than the strokers and the "do-it-yourself " pic a part engine made the least amount of power .... As what Mack was basically saying ...... the combination of parts is the most critical thing when making power .... and the cams with the biggest duration or timing aren't necessarily the best to get ..... neither is the biggest cc's ......



http://www.oldrice.com/Powroll_vs_Yosh_125_Shootout_Pop_Cycling_4.jpg

 

[damann33]

yea thats foresure, as long as what im doing is going to make a difference over stock its all good

 

[themountain]

Check out these dyno charts and specs ......
http://www.oldrice.com/Powroll_vs_Yosh_125_Shootout_Pop_Cycling_4.jpg

Nice link!!...did you see that huuuge cam on the yoshi ...holy sh** and they use a lightened crank and a two ring piston ...nice work

 

[Cactus Jack]

Notice that their exhaust pipe is 1 1/4 inches I/D ? That's 31 mm I/D on a 125 cc engine which allows them to use a 28 to 31 mm carb .....

I've got a brand new old stock mandrel bent MCM race pipe for an SL/XL 125 engine and it's 29 mm I/D ...... the Yoshimura cam has high lift but short split timing so it must have tight lobe centres with high overlap and works well with the big carb and pipe ...... all Yoshi gear was dyno developed and tested for peak performance ...... and it shows on the chart ....

 

[Mack]

That cam powroll is using has some old fashioned timings and is giving those engines some **** numbers. We have access now to much better cams thanks to the work of the aftermarket Japanese companies like yoshimura, takegawa and kitaco etc which have given us computer and dyno generated profiles...the yosh cam is obviously more sofisticated when I look at the numbers and is moving along the same lines as the cams we are using now.

 

[Mack]

well got a chance to look at the motor this arvy. I have only had experience with 59mm pistons in these 140 engines and was able to acheive 11 and 12 compression with 3mm spaced under the alloy barrel and this is just practical with the cam chain length. This is why I suspected the 57mm piston would cause trouble. What I already knew was stock 140 head volume is 15cc, and although the head I'm using has had the inlet sunk and heavy relieving measures 15cc as well because of the flat head valves. Yours maybe slightly more or less. The 57mm piston dome measures 2.5cc.
This means if you used a .5 head gasket and:
stock cylinder 8.7-1 cr
alloy cylinder spaced 3mm 9.68 cr
alloy cylinder spaced 2mm 11.18 cr

This last option is approaching reasonable compression for use with big cams and means the piston to deck will be .4 and combined with the .5 head gasket will give proper squish aswell.

Trouble is... this is the very poor situation for the cam chain length I was talking about. I havn't had a good look at that yet but suspect I may have to make some modifications to the tensioner like extending the idler arm so the roller makes contact further up the chain. Maybe even source some larger diametre rollers as well. I bet the new 150 lifans with alloy cylinders have gone back to the 16/32 cam gearing to negate this problem....a crank gear swap would be a solution but I don't want to have to pull this engine down.

 

[Cactus Jack]

Yes the 16/32 would most likely be the solution ..... (for those wondering why ...... it's because the sprockets are both bigger in diameter to take up chain slack yet retain the proper ratio) ......

As to the Yoshimura vs Powroll dyno ..... you'll find that Powroll used reground and possibly welded stock cams with the wider stock lobe separation ...... note the do-it-yourself motor has a cam with near the same timing and lift as the Yoshi cam yet it makes heaps less power ..... that's because it'd also be a stock regrind with wider lobe separation and mildly angled ramps ... the Yoshi cam would be a faster opening cam with steeper ramps and far greater duration at full lift plus less lobe separation ....... a punchy high revving cam to make more torque with the short stroke crank ...

 

[Mack]

yeah the powroll cams were hardwelded. But that does not limit what you can do with the profile or timings. You can have practically any master grind you want reapplied to that cam and move the centres and advance where you want. Powroll cam had 104 degrees separation and the yosh about 110 degrees lobe separation. Big difference is that the powroll timings are same for each lobe and reversed for each lobe. The timings are a safe and common old timing used to modify cams in all the old stuff. Whereas the yosh cam lobes are tailored in duration and timings for the engine itself. This can only be done with testing and the expensive equipment to make new profiles. The better cams we have for these engines now were developed this way mostly by the Japanese aftermarket companies. All these race cams dealers put forward as their own are really just mastered off one of these jap cams. New cams with the timings we enjoy are not easily made. But these timings have found the sweet spot in these engines and allow us to make HP like the yosh motor did and more.

 

[Cactus Jack]

14 RWHP @ 9,000 RPM with a peak of 15.5 @ 11,500 is a fair bit of power for an old small valve 125 cc 4 stroke engine running 10 to 1 static compression ... Have you seen horizontal 2 valve 125 cc four strokes that can match the same specs at the same rpm running the same static compression ?

Camshaft Technology and Calculations

Here's what the above sites' calculator said about the Yoshi cams specs :

Camshaft Calculations - Lobe Center / Duration

Your Yoshimura 20/50 ~ 53/18 cam has an Overlap of 38.00 degrees and has an Intake Duration of 250.00 degrees. The Exhaust Duration is 251.00 degrees. The Inlet Cam has an Installed Centerline of 105.00 degrees ATDC. The exhaust cam has an Installed Centerline of 107.50 degrees BTDC.

And the Powroll cam specs :

Camshaft Calculations - Lobe Center / Duration

Your Powroll 45/65 ~ 65/45 cam has an Overlap of 90.00 degrees and has an Intake Duration of 290.00 degrees. The Exhaust Duration is 290.00 degrees. The Inlet Cam has an Installed Centerline of 100.00 degrees ATDC. The exhaust cam has an Installed Centerline of 100.00 degrees BTDC.

Are they right ????

 

[Mack]

There is nothing magic in that motor, its because of development like this that we know how to to make it. you can purchase and/or have made everything you need to build a 14hp 125 tomorrow if you wanted. 'Cept now its easier to get your hands on the good bits, its just engineering and money. That article stated the powroll beat on the yosh motor anyhow to my understanding but my point on the powroll is that the 143 with some currently available bits and proper tuning could turn out much better numbers.

Infact the motor I'm building now has basically same bore/stroke as the powroll 145. I will be expecting much more than 10.6 rwhp @ 9000...

 

[themountain]

WOOOW....boys...my head is spinning...talk slower and in english , please ...hahahahaha!!
Nice tech info...you both rule!!

 

[Cactus Jack]

There is nothing magic in that motor, its because of development like this that we know how to to make it. you can purchase and/or have made everything you need to build a 14hp 125 tomorrow if you wanted. 'Cept now its easier to get your hands on the good bits, its just engineering and money. That article stated the powroll beat on the yosh motor anyhow to my understanding but my point on the powroll is that the 143 with some currently available bits and proper tuning could turn out much better numbers.

Yes that's right ..... there's nothing magic about them .... they're just done sensibly ...... Powroll started off by using an XL100 motor which has a lighter crank (that they lightened even further plus stroked) and closer ratios in the tranny whereas Yoshimura simply used an XL125 motor and lightened the crank .... they said the Yoshimura engine made more torque everywhere but was limited because of the set up which obviously gave the Powroll engine an advantage ....... dynos don't show what happens in actual real life conditions .....

Who's to say that the rider on the Yoshi bike wasn't making it stumble and bog with that huge 28 mm Keihin carb whereas the Powroll bike got the jump every time and just hammered off cleanly due to the quicker response and snappiness of the smaller 24 mm Mikuni ....... in other words more ride able .... Remember .... they both still have small valve heads which would work better with a smaller carb on a tight track ..... (no BVH'S back then)

Horizontal engines also have the disadvantage of copping power loss due to windage in comparison to a vertical engine .......

I'm actually in the process of building a 143 cc engine from a grey Lifan 125 Super motor ....

I put all the links on cam info up for interested people (who don't know) to read .... I'm still learning new things myself ....

Here's a few good links explaining how cams work :

Web Cam Inc - Performance and Racing Camshafts / Terminology

LT1howto.com :: Camshaft basic specs and concepts

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