Aprilia RS125 restoration project - Is the engine I've bought actually any good? Episode 2

[@PLASTICPYLO]

1.5mm squish is the factory figure so built to spec. 0.8mm is race/power and not road/reliability spec. Top vid Bud 👏

[@stoneautomotive]

Awesome to hear, few have agreed with your comment so looks like I’m not a million miles off but I have something in store 😬

[@SAVING_ICONIC_MACHINES]

Really enjoying the build mate, keep up the good work.

[@stoneautomotive]

Cheers mate, glad to hear 😎👍

[@dgw4150]

Great update, engine looks pretty good. I could practically smell the GT85!

[@stoneautomotive]

Thanks 😎👍 🤣🤣🤣 I should approach GT85 for supplying them to me for all the advertisement

[@jacklifeonwheels]

Keep going , love rs125s Keep going great bike. Loved this one. Nostalgia

[@stoneautomotive]

Thanks Jack, think we have a big jump in progress coming in the next episode 😬👍

[@paulbudford]

You seem to be measuring both sides of the solder at the same time. You need to measure each side of the solder separately. That's why you are getting such a large squish band. Been waiting for this video. 👌

[@AutoBeta2T]

Yes, Paul. That's what I thought, too. So it's probably about .75 mm which should be okay. Also squish doesn't equate to compression ratio, that needs checking separately. That said it looks like a great engine you have there.

[@stoneautomotive]

Sorry lads should have been clearer in the video, solder wasn’t thick enough so ended up doubling it up

[@sidecarbod1441]

@@AutoBeta2T Well said that man! 🙂

[@sidecarbod1441]

Great 'catch, well done for spotting that.

[@Twinpot1962]

Great vlog, I really admire your camera work and editing. This should be an epic build 👍

[@stoneautomotive]

Thanks and glad to hear 👌 So many over look the hours that go into making a relatively short video so always appreciate these comments 👍

[@skilow3590]

Lovin this series so far 👍

[@stoneautomotive]

Always good to hear 😎👍

[@jamieelliott5205]

I’ve been waiting for this vid to come out .doll on the next vid

[@stoneautomotive]

Hopefully next episode will be worth the wait 😬👍

[@ams668b3]

I have had vhm head on my italkit cylinder for over 5000km and it is still running perfectly

[@sidecarbod1441]

9:45 The squish gap is the squish gap, it won't tell you much about the compression ratio. You could have a head which is running 1mm squish but the combustion chamber volume has been made large by machining the bowl, the CR would still be low. You need to get both aspects of this right if you want the best out of your engine, I would imagine that the squish gap would want to be around 1mm, maybe a touch less. You don't want the gap to get too small as it pushes the gas velocity up too high which can then promote detonation, (the opposite of what a squish head is supposed to do!) Equally you don't want the gap too large because it will stop working as a squish band, it also wastes some of the inlet charge because it will burn too late to be of any use in making power. With your gap at nearly 1.6mm I would say it is 'borderline' not working as a squish band at all. The head volume at TDC will determine the compression ratio, I have no experience with your engine but as a guess you would want to be running around 13.5:1, this would be the geometric ratio, not the 'corrected' ratio (i.e from when the exhaust port closes). I don't like using the corrected ratio, its nonsense in my opinion, basically I agree with A.G.Bell on this point, he is the author of one of the 2 stroke tuning books that I have. (The charge lost out of the exhaust port is forced back into the engine anyway by the reflected positive pressure wave in the expansion chamber). I'm sure someone will come along and give you the CR figure that is best for your engine, bear in mind that pushing up the CR can help the mid range and top end but can cause the engine to not want to rev much past peak power RPM. If you go to high with the CR then clearly you can push the fuel into detonation, or at the least the engine will 'heat fade' when the throttle is held wide open for long enough to allow this to happen. Obviously the fuels octane rating comes into play here.

[@dgw4150]

I was going to say that! Honest. 😂

[@stoneautomotive]

Thanks for the detailed reply, the barrel is going off to PJME 😬 Let the professionals work the magic (above my head 😅)

[@tomBarnes-z5z]

I'm enjoying this and learning good luck

[@stoneautomotive]

Glad to hear 😎👍

[@alextrigg9913]

Set the squish on that Mitaka Barrel/Head. I replaced a standard Rotax Barrel with a Mitaka and it was definitely down on Power!

[@stoneautomotive]

😮☹️

[@tiff9137]

Great content, many thanks 👏🏻🇮🇪👍🏻

[@matejnovak2978]

I have recently rebuild an rotax 122 engine for my rs, measured the squish as well, got to 1,4-1,3 with 0,3 gasket. So I spoke to a pro and measured the volume of the head with oil and that was about right for non-racing 125. So I guess the big squish is ok as long as volume is as well. Ran ti, runs well. On a stock head tho.

[@stoneautomotive]

Interesting, I’m now down to 1mm squish so we shall see how it goes 😅👍

[@GuppyMilk334]

I had one rotax 122 on my aprilia sx 125 and it was amazing engine. I had VHM and 38mm carburator with arrow pipe. It was nice and realiable bike and very powerful. I drove it 3 years all the time and just changed oil and pistons. I tried those rave power valves, but I used it with open valve because i had problems with those power valve systems. E: Im not sure if this is rotax 122/123, but it seems similar. I remember that I needed to put 800ml oil in it, but it said 600ml on the side. If you used 600ml you brake yellow plastic gears. I would check that out.

[@stoneautomotive]

Mines the 122, shall be interesting to see how I get on with the power valve set up. Thanks for the tip regarding the oil 👍

[@mulletto27]

Hi chap - let me check, but I might have an ultrasonic bath you can have for free if you really want to have one for your carb builds. I’ll have a look tomorrow and come back to you. Top vid, shame about the chassis front bracket but I’m sure you can get a frame cheap/bolt something to that front end and make a clock bracket 👍🏻

[@stoneautomotive]

Wow that would be awesome! Don’t stress if you don’t have one, I should really invest 😅 Think I have a very good solution for the frame, more to come on that in the next episode 😬👍

[@stoneautomotive]

Ping me an email if you do have one 😬 [e-mail]

[@keithtiplady8893]

Hi, great video, I’ve just done a rebuild on one of these, I ended up buying a Chinese fairing kit. Pretty happy with it, little bit of dremmel work but not much.

[@stoneautomotive]

Thanks 👍😎 Yea I think the race kits I’m looking at will require some “tinkering” 😅

[@supertedogpriken]

The jetting seems ok. Had that been my bike i would not hesitate to fire it up with that carb setup. It probably was the carb for that engine/bike, it just got pulled of and someone forgot to empty it for fuel when doing a rebuild on the engine(/bike) It looks like you are missing some parts for the Power valve. Not sure what mode you have there. but there should also be a "housing" and an adjustment knob(black housing and red knob, or alu frame and black knob) Keep them videos comes, love to see the Rotax/2 stroke content.

[@stoneautomotive]

Thanks for the feedback, like you say a few others have mentioned the jetting is about there 👍 That power valve is complete so I’m told, there is a more advanced version which is adjustable but this ones fixed opening (let’s just hope it works 😅)

[@CostelloPlays]

Great video. Great channel 👍🙂

[@stoneautomotive]

Thank you 👍😎

[@dosacole2201]

there are 3 different vhm heads, i just got mine a few days ago, i ordererd a standart one bute there are 2 others. there are 11,50cc wich is a higher compression ratio then there is the 11,60cc wich i orderd with standart compression and there is a 11,80cc one with lower compression ratio. with the 11,60cc head i now got a 13,48:1 compression wich is exactly what i wanted. with the standart head my squisch whas way off with 2,1mm, even with the thinnest gasket i could find. ur 1,5mm would be bang on for street use. The 155 main jet is standart set up in the 34, i am now running a 158, cause i got a few mods done to the engine and around

[@stoneautomotive]

Good to know! Strange there’s no markings to let you know which model I have.. The squish is now set at 1mm - the barrel/ head was sent away to Paul at PJME and he machined the barrel down to increase the compression 😎

[@bobbakdaj6888]

Sound mate, yeah, I got some rik Rings instead of the mitaka 140cc rings there ment to be one of the best , Japanese rings and engine is all done and frame work completed now off to the powercoaters next month, got new set of raidtors coming soon and a graphics kit from france. I'm on the worst part now sanding all the pannels 😂 in order to down to spary them

[@stoneautomotive]

The painting part is so satisfying but as you say the prep is a nightmare 😅

[@KTM-Beta]

Regarding squish and high compression, from an MX point of view. It isn't always a good idea to run a higher compression because you might loose some overrev capabilies. Therefor loosing power and revs on top for a small gain at low revs. Since small displacement engines need revs to produce power I wouldn't raise the compression by alot, especially if you don't intend to put some hours dynotune it to get it working right. Short, some stones is better left unturned 😊

[@stoneautomotive]

Agree, you can certainly go to low on the compression, detonation can then also start to occur 🥴 1mm squish appears the best setting for a road bike, with it being 1.5mm it’s going off to Paul at PJME for a slight tweak 😬

[@DoRC]

It looked like when you had the original measurement t piece made there was only one thickness of solder on either side but then when you were measuring in the end you were measuring two pieces together. Was this just because you weren't getting any reading with the single thickness?

[@stoneautomotive]

Correct, I should have mentioned that in the video

[@DoRC]

@@stoneautomotive okay that's what I figured I just wanted to make sure you weren't for some reason measuring both sides at the same time.

[@tyler_1186]

that powerblade thing is that the nuematic one i have that on mine and is my first rs so figuring everything out as when it comes to selling it end of the year wanna do a nice clean up and just wanna know everything about it to be honest quite knowledgeable already just new to the road bike 2t

[@BikesofRye]

Engine is spanking! Also I noticed you used a fancy little attachment for your torque wrench to get on those head nuts - what where they!?

[@stoneautomotive]

Crows foot spanner, can get you right out of trouble 😅 www.ebay.co.uk/itm/234953648537?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=X_IuMAaJS4q&sssrc=4429486&ssuid=CKFRglVnR7S&var=&widget_ver=artemis&media=COPY Been following your latest project, soul destroying the head ache it’s given you but fair play for cracking on 👍

[@ragnarironspear1791]

Looking mint

[@stoneautomotive]

Cheers mate 😎👍

[@krazed0451]

K21 needle (look up the chart and measure what's in it, might already have one) on top or second clip, 158-160 main, 34-36 idle jet, B40 emulsion tube. Definitely needs less squish, not sure how much less though, I'd guess in the 1.15mm range... Although running at 1.5mm will be fine most likely. Start with the fatter jets and lean it out one size if a plug chop indicates you need it.

[@stoneautomotive]

Yep I have a solution now for the squish, PJME will be working there magic!

[@krazed0451]

​@@stoneautomotive I look forward to hearing the little blighter sing 😁

[@mozer30]

I’d assume that vhm will specify a squish clearance of 0.8mm, which will also give you the correct combustion chamber volume. As of your measurement of 1.5 mm, not only are you excessive on the squish clearance, but you will also be low on compression. Using a thinner base gasket will get you closer to the desired spec, but I think you’ll struggle to find a base gasket thin enough to bring it into spec. I’m guessing that the mitaka cylinder may be slightly taller than the stock cylinder. You should also perform a pressure test once assembled.

[@stoneautomotive]

We have a solution regarding the squish, more in the next episode 😬👍

[@mozer30]

@@stoneautomotive good to hear, I’ll look forward to it 👍

[@massimilianokemp]

Great work!😊

[@stoneautomotive]

Thank you 😎👍

[@katywalker8322]

Looks like that barrel has had a liner fitted (standard it would be a plated bore, and the Mitaka barrels also use a plated bore). If you get oil in the ignition side cover then you have a big problem! Jetting sounds about right. The needle valve looked worn (from memory, brown end of the needle valve is the later type suitable for fuel with ethanol in it).

[@stoneautomotive]

PJME completed the top parts so should all be in good order 😬👍 Thanks, no gasket for the ignition side cover though to prevent dust etc entering? Good to know regarding the needle valve 👍

[@twosqueaks4839]

@@stoneautomotive , think silicone is meant to be used between the ignition cover and the engine

[@stoneautomotive]

@@twosqueaks4839 that was my later thoughts too 👍

[@bobbakdaj6888]

What jetting is in that carb im running a 155 main with 37.5mm pilot with the 34mm carb and 140cc mitaka and dual stage reeds and runs faultless i know some one who has 4 mx 125s and runs this same set up without issues

[@stoneautomotive]

Reviewing comments I’m “ok” on the current carb set up 👍

[@kavonmchellon4651]

That fuel has been sitting in that carb for possibly decades, I got a couple mopeds here in the states that haven't run in at least 30 years that looked similar

[@stoneautomotive]

Yea must be, the only thing that would make any sense!

[@TurboRichie]

I wouldn’t go under 1mm squish on the road. I would guess that 0.8 squish would be too tight even for premium pump fuel. What people seem to mis understand is that making the squish mega tight also reduces the cylinder head volume… in turn causing the compression ratio to be much higher than what is safe on pump fuel.

[@stoneautomotive]

Yep a few have advised 0.8mm is too much for a road bike, barrel will be going back to PJME for some magic to happen 😬

[@MrBurgandy25]

Are you going to replace the plastic counterbalance gears with the metal ones with more teeth?

[@stoneautomotive]

No plans to replace/ upgrade the plastic gears (this will be more of a weekend/ local play bike) I would be surprised if I cover more than a 1000 miles in my ownership as I’m building it to be more of a display piece with a handful of rides a year

[@TheHulmie]

Id speak to PJME and ask their advice. I've had work done by them in the past and they really know their stuff

[@stoneautomotive]

Paul from PJME reached out to me, really knowledgeable chap 👌 will be doing some further bits and pieces with him shortly 😬

[@protoperipoli3196]

Looks like your idle jet is missing. It should be a 5mm thread, 40 to 45. Main jet is 155 is fine if you use the original airbox, then it depends on the filter thickness, exhaust and so on. 155 is a good starting point, though you might need to go down to 150 or up to 160 according to your specs. Without the idle jet I don't think you'll ever be able to idle, it'll always be too rich below 2000 rpm. 1.5 mm squish gap is standard. With the original Gilardoni Aprilia cylinder usually needs 0.3mm or 0.5mm to reach 1.5mm squish gap, though I've been told that the Mitaka kit might need thicker gaskets. I wouldn't go lower than 1mm. You can measure the compression ratio, but there's always a margin of error even if you use the correct technique. MItaka kits seem to be reliable enough, though the fusion is not perfect, that might explain why they ported it a little.

[@stoneautomotive]

Thanks for that, shall have a proper look over the carb when the engine goes back, something simple like that could cause a lot of headache 🤦‍♂️ Barrel and head are back from Paul at PJME and skimmed to 1mm squish 😬

[@protoperipoli3196]

If you need to buy the idle jet, I recommend the 'tall' ones. I know some people on the 28 remove the idle jet when they go racing, you need to screw the idle screw all the way in, they do that because their engines run at 13/14k rpm and they might seize if they use the engine break after going flat out all the time. Having a very rich idle might help extreme users, but I don't think that's your case. Let me know how it goes

[@bobbakdaj6888]

And always premix the 2 stroke oil tank is unreliable had a mx 125 now have a sx 125. 25ml 2 stroke oil to a litre of fuel is spot on never know to have a fault

[@stoneautomotive]

Yep it will be on premix 😬

[@TEAMVISKAT81]

nice rotax 125 :P

[@mikesphoenix_e46m3]

looks really tidy mate lets be honest its better comming home with abit of man flu than a gunky toe 😄

[@stoneautomotive]

Oh yes! My boys trips have done me far worse in the past 😅

[@rm19-racingchannel62]

1.00mm is the correct squish 0,8mm is to small, and wil get pre detonation

[@stoneautomotive]

This is what I’ve been advised, thanks for confirming too (good to know thats considered the optimum for roads bikes 👍)

[@rm19-racingchannel62]

@@stoneautomotive I race the same cylinder on my racing kart. And there it’s even set in the rules to not go under 1.00mm gap. Check your spark plug gap too it needs to be 0,7mm for best ignition. And the powervalve should open at 7500tpm for the best torque and power band. There is a kit for the 125RS that makes it possible for setting up the powervalve at the RPM you like it the most.

[@kasperfagard5803]

Use a 165 or 175 main jet

[@stoneautomotive]

Thanks, need to do some more research with running premix

[@garyalexander2480]

0.8 squish

[@stoneautomotive]

I’ve been advised that’s for race engines on better fuel than pump, more of that on the next episode 😅

[@Martin-v2x9s]

Mitaka Cylinders are Scrap👎

[@stoneautomotive]

I have been hearing completely the opposite, early ones had issues but the later produce ones fine

[@malcolm.703]

👍👏🏍️👏👍