My new bike ate my shorts!

[kiwigasbikes]

Update time. parts are flooding in from China, Japan and Russia.
no, the parcel from Russia is from Snezhana's mum.
Ive split my cases and Im about to start truing a 30thou whoopie in my crank. but whats this 2mm squish gap? haha- that's OK- It's from the 'new'-new engine that arrived yesterday. you need one for spares when they are this cheap.
I was planning on a nice two month long run in on a std engine, get that saw carb working well, then after 2 months strip it down, stuff the crankcase, balance it, tickle the ports, open the baffle a little. buy it a bottle of wine and a nice dinner, whisper nice things to it Then go out and do something epic like a coast to coast ride. Its about 180 miles where I live. 9 hours in the saddle- cos I deserve it.

 

[ImpulseRocket]

That's not a squish gap, that's a squish chasm.

 

[kiwigasbikes]

Well- Im back, Im truing my crank , Im stuffing the cases. I have my nice SKF main bearings- and now Im trying to figure why all the sellers of chinadoll main oil seals insist that one is 15mm and the other is 14mm - when they both measure up the same?

 

[ImpulseRocket]

Well- Im back, Im truing my crank , Im stuffing the cases. I have my nice SKF main bearings- and now Im trying to figure why all the sellers of chinadoll main oil seals insist that one is 15mm and the other is 14mm - when they both measure up the same?

Truing a crank is my favorite part of a 2 stroke build. I do it with every engine I put together. May as well since I built a stand to do it with and I have the dial gauge and patience for it. Once you do it a couple of times it's actually quite easy to get a crank to within .001"/.025mm of total runout between both sides, which is what I try to aim for. Not including any setup time I can probably get to that point within 20-30 minutes.

The real trick comes during assembly of the case halves and trying to avoid pinching the crank again. I will test fit my new bearings to the crank before I install them in the case, and then slowly resize the end of the crank with emery cloth until the bearings are just barely able to slide on to the crank without binding. I also use finer emery cloth to polish the shaft ends a little bit to help with seal life and sealing. Just don't go crazy and aim for a mirror polish either as you still want some "texture" for oil/grease to sit in and provide lubrication. 400 grit is more than plenty.

As for the seals, you can also find them on your own as long as you have the dimensions. Viton seals are far superior to the standard stuff these engines come with. I also like to use a non-curing sealant/RTV such as Hylomar Blue on the outer edges of the seals when I install them to help retain them and provide a little extra sealing. If these engines had simple bearing retainers I wouldn't bother, but they don't. I also do this because I run my crank bearings with no seals at all and rely only on the case installed seals. So far it has never caused me an issue. I do know that you can find a seal retainer for the magneto side on ebay.

Don't mind my nerdy detail filled engine building stuff. I go overboard when assembling my own engines as I always have a focus on optimization and taking any steps I can to ensure or improve reliability and functionality.

 

[kiwigasbikes]

Truing a crank is my favorite part of a 2 stroke build. I do it with every engine I put together. May as well since I built a stand to do it with and I have the dial gauge and patience for it. Once you do it a couple of times it's actually quite easy to get a crank to within .001"/.025mm of total runout between both sides, which is what I try to aim for. Not including any setup time I can probably get to that point within 20-30 minutes.

The real trick comes during assembly of the case halves and trying to avoid pinching the crank again. I will test fit my new bearings to the crank before I install them in the case, and then slowly resize the end of the crank with emery cloth until the bearings are just barely able to slide on to the crank without binding. I also use finer emery cloth to polish the shaft ends a little bit to help with seal life and sealing. Just don't go crazy and aim for a mirror polish either as you still want some "texture" for oil/grease to sit in and provide lubrication. 400 grit is more than plenty.

As for the seals, you can also find them on your own as long as you have the dimensions. Viton seals are far superior to the standard stuff these engines come with. I also like to use a non-curing sealant/RTV such as Hylomar Blue on the outer edges of the seals when I install them to help retain them and provide a little extra sealing. If these engines had simple bearing retainers I wouldn't bother, but they don't. I also do this because I run my crank bearings with no seals at all and rely only on the case installed seals. So far it has never caused me an issue. I do know that you can find a seal retainer for the magneto side on ebay.

Don't mind my nerdy detail filled engine building stuff. I go overboard when assembling my own engines as I always have a focus on optimization and taking any steps I can to ensure or improve reliability and functionality.

Reading that reminds me of all the mid 1980s 125MX bikes Ive built. and my outboards- 700X race Mercury with 120hp! I enjoy the work too.
But!- we have not discovered why the people who sell sell seal kits for China dolls insist that One is 15mm - one is 14mm when the crank is 15mm both sides?

 

[ImpulseRocket]

Reading that reminds me of all the mid 1980s 125MX bikes Ive built. and my outboards- 700X race Mercury with 120hp! I enjoy the work too.
But!- we have not discovered why the people who sell sell seal kits for China dolls insist that One is 15mm - one is 14mm when the crank is 15mm both sides?

I can't answer for them.

 

[kiwigasbikes]

Its a rainy day in Noo Zealund so Im in the shed Trenching my cases and matching ports.
on the left is 1/2 an hour with a carbide bit and sandpaper in my cordless drill. On the right is the RH case with the 3mm stuffing plate epoxied in and waiting its turn. you can see the amount removed to match the transfer ports in the barrel.
Im really enjoying getting back into porting. last ports I worked on was in 1992!

 

[DAMIEN1307]

Im really enjoying getting back into porting. last ports I worked on was in 1992!

What took ya so long then ???...lol...lol...lol.

 

[Gordy]

Its a rainy day in Noo Zealund so Im in the shed Trenching my cases and matching ports.
on the left is 1/2 an hour with a carbide bit and sandpaper in my cordless drill. On the right is the RH case with the 3mm stuffing plate epoxied in and waiting its turn. you can see the amount removed to match the transfer ports in the barrel.
Im really enjoying getting back into porting. last ports I worked on was in 1992!View attachment 229630

Imo trenching is more harm than good. Where'd you get the stuffing plates?

 

[ImpulseRocket]

Ahh, good old case flowing. That is a habit I got tired of a while back due to the sheer amount of time it takes. Just remember, short corners = bad. It also helps sometimes to use epoxy (JB weld) to fill in some areas too so you can cut it back and make things as smooth as possible.