Oldgeek's 90cc+ longcase build: Update it's a 103cc

[oldgeek]

I quickly hacked the new piston up a bit, just cleared out the transfer area in the skirt. This new piston started out 8.3g heavier than the old piston, it's skirt is about 2mm longer than the old one, and its pin to dome is slightly longer than the old one. I trimmed 2.8g from the skirt. I think that is all I am gonna do to it.



Before trimming


After trimming

[oldgeek]

I finally located my 54mm ball hone, so I ran it through the cylinder and started the cylinder and piston cleanup.

It looks like since I already have a 21mm Dell carb on hand I am going to use it, at least for now. Might upgrade to a 24-26mm PWK later if necessary. I reamed out a stock intake so it would match up to the 21mm dell a little better.

I pulled out the nonrunning streetrace Yamati scooter and sat on it today it's been a while, and I am looking forward to riding it again, this time as a 103cc.

[Jwhood]

Like the piston work my painted cases are hanging waiting to be built just wanna find a small frame scoot to put it in,the Tgb is my d.d or I'd slap it in there,plus I wanna make a wheelie machine with the 103 engine and also wanna do some port work on my 54mm to get the most out of it,the cylinder definitely needs work casting was not the best but I'll get'er there

[oldgeek]

Nov 26, 2017 21:35:37 GMT -5 Jwhood said:

Like the piston work my painted cases are hanging waiting to be built just wanna find a small frame scoot to put it in,the Tgb is my d.d or I'd slap it in there,plus I wanna make a wheelie machine with the 103 engine and also wanna do some port work on my 54mm to get the most out of it,the cylinder definitely needs work casting was not the best but I'll get'er there

I wish you were close by, I have a zip clone in decent shape you can have. It was my other 90+cc project fail. Probably going to scrap it.

[Jwhood]

Nov 26, 2017 22:12:57 GMT -5 oldgeek said:

Nov 26, 2017 21:35:37 GMT -5 Jwhood said:

Like the piston work my painted cases are hanging waiting to be built just wanna find a small frame scoot to put it in,the Tgb is my d.d or I'd slap it in there,plus I wanna make a wheelie machine with the 103 engine and also wanna do some port work on my 54mm to get the most out of it,the cylinder definitely needs work casting was not the best but I'll get'er there

I wish you were close by, I have a zip clone in decent shape you can have. It was my other 90+cc project fail. Probably going to scrap it.

Damn wish I was closer I'd save it from the crusher,I've been looking for a prebug but no luck yet
Where u live at?

[oldgeek]

Nov 26, 2017 22:20:26 GMT -5 Jwhood said:

Nov 26, 2017 22:12:57 GMT -5 oldgeek said:

I wish you were close by, I have a zip clone in decent shape you can have. It was my other 90+cc project fail. Probably going to scrap it.

Damn wish I was closer I'd save it from the crusher,I've been looking for a prebug but no luck yet
Where u live at?

Myrtle Beach, SC 29577

[Jwhood]

Nov 26, 2017 22:38:02 GMT -5 oldgeek said:

Nov 26, 2017 22:20:26 GMT -5 Jwhood said:

Damn wish I was closer I'd save it from the crusher,I've been looking for a prebug but no luck yet
Where u live at?

Myrtle Beach, SC 29577

Damn if you was in n.c I might've done a road trip!!hahaha

[oldgeek]

Now I am aggravated. I cleaned everything up for final assembly, put sealant on the base gasket,installed the piston and cylinder and torqued the head bolts. I purposely did not seal the head yet because I knew the squish would need to be played with. Somehow I now have contact between the piston and cylinder despite having a squish between .75-.88 depending where you check. I cannot find the place where contact is occurring despite several attempts and methods that I tried. I even chucked the head up in a drill and milled it a bit in a couple places but it still makes contact, I just cannot find out where. I was wanting to run the squish <1mm but I may have to give up and settle for +1mm. I had the same issue on my last attempt at a 99cc build with this kit. At the time we just thought I ran the squish too tight, but now I am thinking the head is milled crooked or something. The only thing different parts wise between this build and the last attempt is this time I have a new piston kit.

[benji]

Try spraying something like Windex or wd40 on it then bolting it on and that should leave a wet mark where it's hitting.

[benji]

Wait, is that the right head? Does the diameter match up? Maybe it's for a smaller bore.

[90GTVert]

How bad is it? Stopping the piston so you can't rotate it anymore or you just feel or hear them "kiss"? Not sure that it matters, just curious. I've never had one show good clearance and then hit.

The bore and chamber alignment that Benji mentioned is a good call. Definitely check that the best you can. You may even be able to feel around in there with solder or wire either through the plug hole or exhaust port and see if you can feel a lip anywhere. One of those little bore scopes could do it too if you have one.

I usually do + pattern squish checks when it's tight. One at the top, bottom, and each side. If you do that and the head is machined at an angle other than perpendicular to the bore, you should notice the clearances being off across the measurements.

Is the angle of the squish band flatter than the piston crown? Maybe it makes contact toward the center where the crown rises more rapidly than the band falls away? If so, a solder or clay squish check would show you that too as long as you cover the whole band.

[oldgeek]

Nov 28, 2017 6:19:51 GMT -5 90GTVert said:

How bad is it? Stopping the piston so you can't rotate it anymore or you feel or hear them "kiss"? Not sure that it matters, just curious.

I usually do + pattern squish checks when it's tight. One at the top, bottom, and each side. If you do that and the head is machined at an angle other than perpendicular to the bore, you should notice the clearances being off across the measurements.

Is the angle of the squish band flatter than the piston crown? Maybe it makes contact toward the center where the crown rises more rapidly than the band falls away? If so, a solder or clay squish check would show you that too as long as you cover the whole band.

It just kisses sometimes, depending upon how the head is bolted up.

Squish is all over the place .84 at the flywheel side, .97 at ex and intake, 1.07 on variator side IIRC.

They did not machine the entire top of the replacement piston, just the very center. I have seen other kits the same way, but this one is uneven I think. I am going to send the head and piston to 190mech to be cleaned up a bit hopefully.

[vlatx]

Dont run to tight squish on that engine,1mm+ is more than enough,when the deposit form oil is colected over time it will get smaller and smaler.

[ryan_ott]

Those 103’s need alignment dowels. The last one I had was the exact same way. Sometimes it would touch. Do you have different heads to try?

[190mech]

Indexing the head to the bore is the best way to make an even squish,requires careful centering and drilling both for a few roll pins for repeatable assembly,or a step cut head does the same if possible..Good article here;
www.rd350.info/articles/squishing/squishing-part2/
Its said that squish should be 1% of stroke (.45mm),damn close for this junk we are running!Remember the squish band pushes the mixture into the chamber bowl to suppress detonation,any more than needed will allow combustion to expand toward the edge of the piston,then we are going to start melting aluminum pretty soon..Its a fine line that each engine has and no two are the same..Ive got a recent Chinarelli build that makes a loud clack at revs,gotta take some meat out of the squish area to allow for the cheap/sloppy parts...