mattyslimz
Scoot Enthusiast
Posts: 222
Location: Northern Virginia
|
Post by mattyslimz on Sept 13, 2020 6:30:23 GMT -5
wow! this is some serious budget minded building here, nice planning/research. Extreme in the sense of word both saving money and craft time , I dont blame you one bit, after all things shouldn't have to be all that expensive on these 50cc scoots.
Calculation of your duration numbers seem pretty good considering you are using an China bore and piston/ring(s) I assume, god only knows what numbers folks get out of the box on these, the gaskets i've seen in person and in pics have not been good, both new and on disassemble of the no name kits gaskets. Ports usually come with excessive casting flash that porting or extreme chamfering is REQUIRED. A decent and CHEAP 70 kit is Motoritecs kit from Taiwan.Its a better kit to use if you are doing all this crafting/porting (I use the word craft instead of work in your case because its obvious you enjoy the building process) the Motoritec kit is on Ebay from seller name autotech355 I believe the gentleman's name is Carlos (a great seller I may add), ive purchased a few odds and ends at VERY low prices in the past like gaskets that are of good quality . Reviews of his big bore kit have been good and there's a port map on one of his kits in the 2 stroke performance thread here on 49ccscoot. Chances of damaging the cylinder skirt on an better made cast cylinder will be much lower using something of better quality, a big chip off one while in the process of getting it to match your newly formed case is going to ruin your day.
For the money I would consider the Stage 6 streetrace or an Polini sport, I got a deal on my S6 kit ($115) plus shipping, from a sale scooterattack/maxi was having. The piston itself makes up for the little extra it cost. The Vertex pistons S6 sends you are very nice, the quality is evident and longevity/performance has proved it self to me 10 fold with these pistons. Going high compression like the numbers your looking for are going to require a strong piston..
**Edit** went back and read your thread again, I guess i must've missed the part where you have pictures posted, this old laptop doesnt like to load things to fast. You've already did some good work to an undesirable kit, fingers crossed she rips and lasts long enough to keep updates flowing.
|
|
|
Post by lokstar on Oct 15, 2020 21:11:41 GMT -5
Hey Guys, after a little hiatus to take care of some family stuff, I've finally had some time to get back into the scoot. I did a stock take and inspection of all the parts to remind myself where I was up to. I assembled the crank and ported cases. Put the piston on with no rings and slipped the base spacer, gaskets and cylinder over and torqued it down to check port timing. I took 6 measurements of each port and worked out the average. I was pleasantly surprised to find 189exhaust and 128Transfer which is pretty close to my initial calculations and even better to find that the piston came flush the port floors at BDC. With the base spacer the piston was around 2.5mm under the deck height at TDC so I faced it down on my mill but the cutting tip came loose mid way though the second pass and left a nasty gouge before could I shut it off. I thought I'de ruined the cylinder as I hadn't left much room for error. I did a quick check and it was salvageable with s light sand. I re assembled and the piston was now .8mm below the deck.... that was lucky!!! I put my recut head on to check the squish but the first test didn't even touch the 1.2mm solder. I put the head in the lathe and faced it right down so there was no lip and recut the squish band down to 7mm wide to allow more combustion volume as compression would now be though the roof! another check showed .7mm of squish. obviously I wont be using a head gasket, only copper spray. again, this is bang on my initial plan. I fitted the rings and wanted to do a quick cranking compression test but I need to install the starter first and it was getting late. so I'll do that in the next week or so to make sure we're in a safe range before do the final install of the cylinder and head.
|
|
|
Post by aeroxbud on Oct 16, 2020 11:43:54 GMT -5
It's great when things go as planned. Should be near optimal for this kit.
|
|
|
Post by rocketbooster on Oct 19, 2020 13:38:15 GMT -5
I have a question about ignition. Where spark is ignite? After metal pice of flywheel miss pulse coil, or very end od this pice before it miss. I'm trying to set this of but im confused Sorry for bad english best regards from Poland
|
|
|
Post by 190mech on Oct 20, 2020 4:30:42 GMT -5
I have a question about ignition. Where spark is ignite? After metal pice of flywheel miss pulse coil, or very end od this pice before it miss. I'm trying to set this of but im confused Sorry for bad english best regards from Poland Spark is at the end of the bump on flywheel,here is a pic on this page; www.sportdevices.com/ignition/ignition.htm
|
|
|
Post by lokstar on Oct 20, 2020 17:03:45 GMT -5
So I fitted the reed block and all the starter gear. Hooked up the compression gauge and spun the engine over with a spare battery. I nearly died when I saw the gauge jump to 220psi after about 2 seconds of cranking. I fitted a .45mm head gasket and tired again. this time it only showed 145psi. Found a .35 gasket, that read 155psi. These tests were just to tell me how much volume I need to remove from the combustion dome in the head to get my desired 175psi. obviously I cant run a gasket or i'll loose my desired squish. I put the head back in the lathe and removed some material. as I was assembling for another test, I was torqueing the head down (10lbs) and heard the dreaded crack I thought ide snapped a head stud but it infact pulled the treads from the cases. disheartened, I packed it in for the night and pondered potential remedies. I've used helicoils to fix similar issues in the past but its never sat right with me. There's also not a great deal of case material to drill and tap out for a helicoil and it could potentially fail and ruin the cases to a point of unrepair. In saying that, it could be done and some have no doubt done it in the past on these engine but I wasn't convinced so I ordered some larger M8 studs to replace the M7's. When they arrive I'll replace all 4 studs with the larger ones as I don't want to have miss matched studs(different steel has different tensile strength so when torqued down I want the pressure to be even to give a good seal and allow for no head leaks) some slight delays but thems the brakes.... As a wise youtuber sais "Easy isn't worth anything"!
|
|
|
Post by nikola11 on Oct 20, 2020 17:43:15 GMT -5
What a shame...But it is wierd that you were able to pull the threads at only 10lbs. That is a little under the factory torque spec for most minarellies if I am not mistaken.
|
|
|
Post by lokstar on Oct 20, 2020 20:24:11 GMT -5
yes, I was surprised too! When I initially fitted the studs in the cases, I didn't plan on having to remove them again. I double nutted them and torqued them to 15lbs. I have actually had them come loose on me on other builds with tighter specs. With all the mock ups ive only been going to 10 with the nuts but was planning on 12lbs for final assembly. I have a funny feeling the constant fitting and removal has weakened the threads and the initial pressure of 220psi may have just been the straw that broke the camels back so to say.
|
|
|
Post by nikola11 on Oct 21, 2020 3:34:24 GMT -5
Hm, maybe you do not need to tighten the studs in the block so much. I usually just snug up the studs (aprox 3-4 lbs) and never had one back out. Also you should have in mind that that is a chinarelli block so maybe the aluminum is not the same quality as an original minarelli block.
|
|
|
Post by lokstar on Nov 2, 2020 23:20:48 GMT -5
ok guys I know I drag the chain a little with keeping you updated....sorry about that. So the new studs arrived and I drilled and tapped the new threads for all 4 studs. I only did them up to 10LBS this time but used a little locktight. The cyl slipped over the larger studs but the holes in the head needed to be enlarged slightly. Rather than re shape the combustion chamber again to reduce the compression.... I already ruined one head and I don't have any more spares. I found some .28mm aluminum sheet and cut a head gasket from it. fitted it all back together and ended up with .95 squish at 165psi. they're not quite my target numbers but its close enough for me.... I'm getting impatient.
|
|
|
Post by lokstar on Nov 2, 2020 23:41:19 GMT -5
A friend of mine caught wind of my little mad science experiment and wanted to build a scoot too. In his haste went out and picked up a 2009 Piaggio Zip with a spare seized engine for next to nothing. Hes not really mechanically minded and not knowing anything about the Piaggio engines I did some research for him. Turns out you can really get them to boogey however parts are a little on the dearer side opposed the Chinese stuff ive been using which scared him away. He sold the Zip for a small profit but I kept the seized engine.... well because I'm a hoarder lol. I few days later I watched Brent's overange alternative vids on you tube and checked the rear pulley on the seized Piaggio engine to see if was the same as he used in the vid. My eyes lit up when I noticed the part number. Now I have a free overange rear pulley . I cut the halves down in the lathe to 128mm and modded the cases so it would fit. This morning I picked up a slightly longer belt (804mm opposed to the stock 788) from a mate in town who has a bike shop. Really hoping it works well, giving a deeper 1st gear and not sacrificing to much top end. I'm planning to put the built engine back in the bike tonight and start getting it all finalized ready for some carb jetting which should take much as I already have a base line to go off from the previous build.
|
|
|
Post by aeroxbud on Nov 3, 2020 15:53:54 GMT -5
Coming along nicely. You can get some good power out of the Piaggio engine. It looks a lot stronger built than the Yamaha ones.
|
|
|
Post by Steve B on Nov 4, 2020 10:19:03 GMT -5
Nice job with the compression tests.
|
|
|
Post by lokstar on Dec 8, 2020 22:58:16 GMT -5
Hey guys, Another update... ive been a bit slack. Ive held off using the Piaggio OR idea for now.
I fired up the engine for the first time a few weeks and gave it a few heat cycles then re torqued the head, gave it a jetting and variator tune and good going over before a road test.
The first ride was a success. No more than half throttle. It was revving and pulling nicely for a quick tune. It felt and sounded a slightly lean so I upped the main from 98 to 100 and took it for another test ride the next day. This time I rode around for about 10km and just nearing home it had a small seize. I pushed it home and inspected. There was aluminum specks on the plug and a noticed oil weeping from between the cyl and the head. I pulled it down...
The piston which I though shouldn't be too bad after a small low speed seize, was actually completely shot! grooved and distorted all over. The cylinder wasn't as bad but required a good hone. Theres still some slight score marks but I deemed it reusable. It appears the head gasket I made hadn't sealed properly in one tiny despite using copper gasket spray and double checking the head bolts. This would explain why it idles nicely but felt a little lean up top. when the revs picked up it would have been sucking air and leaning out the mixture. To add insult to injury, I hadn't tripped the inside of the gasket exactly to match the bore and the tiny protruding lips were melted and sucked down between the piston and bore... this is why the piston looked so bad.
I ordered a new piston, rings and .3mm gasket. Re assembled after honing the bore and facing the head and deck on glass. I also bumped back the ignition advance slightly to eliminate that causing any issues too. Compression was 160psi with .9mm squish. It fired it up last night and it idled nicely for 5 or so mins. Ill give it another few heat cycles and hopully do some test rides this weekend.
|
|
|
Post by Steve B on Dec 9, 2020 8:54:16 GMT -5
You should put up some videos.
|
|