I f***ed up my big bore and now my bike is garbage. - Page 5

grumpyunk · 05-04-2021, 11:19 AM

Are the counterweights on the crankshaft colliding with the wrist pin boss? If that's the case, the parts were either incorrectly machined or not designed to fit. Out of the box.
No thicker head or base gasket would have any effect. No assembly technique would change the dimensions machined into the parts.
Question is why does it seem to be quiet until rpms are increased, or did I hear it wrong?
Can you put up a picture of the counterweights? Would be interesting to see the contact pattern.
tom

ChopperCharles · 05-04-2021, 11:27 AM

I will use blue machining layout fluid on both surfaces and refit the piston so you can see the contact.

So, it still made noise at idle. More than I thought it should. The reason it made MORE noise as RPM increased is likely the loads increase and the tolerances tighten as piston speed increases, and instead of slowly rubbing by the counterweights it was now slamming into them at speed. Thermal expansion is also a probable reason.

It also explains why the noise was two times the speed of the exhaust note. 4 stroke engine, piston moves up and down twice for each power pulse.

And yes, that's exactly what's happening. The wrist pin boss is not properly machined, and thus incorrectly machined out of the box.

Pic of counterweights is above.

Charles.

ChopperCharles · 05-04-2021, 11:41 AM

So I bought my kit from GPX Moto, and it's the RTC kit. The RTC kit is also on AliExpress, and if you look at the pics on AliExpress the wrist pin boss has a lot more machining.

So it appears I got a defective big bore kit.

Charles.

Emerikol · 05-04-2021, 03:10 PM

Quote:

Originally Posted by ChopperCharles

So I bought my kit from GPX Moto, and it's the RTC kit. The RTC kit is also on AliExpress, and if you look at the pics on AliExpress the wrist pin boss has a lot more machining.

Charles.

Well, I mean, your wrist pin boss is pretty well machined now, too!

ChopperCharles · 05-04-2021, 06:49 PM

Ugh, unfortunately GPXMoto is out of big bore kits right now. Waiting on news when they'll get more. If they're not coming in soon I'm going to put the original piston back in.

Charles.

bogieboy · 05-04-2021, 10:13 PM

My personal opinion, which may not be worth much, is just grind down the bosses til you have clearance and run it... if it was going to stress the rod or anything, it likely would not have even turned over completely the first time you went to fire it... i would take about 5thou off that piston's bosses and run it....

ChopperCharles · 05-04-2021, 10:33 PM

That’s a great idea except I still have no source for a replacement head gasket. I am worried about stress fractures in the piston.

Charles.

bogieboy · 05-05-2021, 07:39 AM

I wouldnt worry about stress fractures, and i would reuse the head gasket and ship it..... maybe think about getting a piston and headgasket down the road as a spare, but i would bet they will be fine....

TxTaoRider · 05-05-2021, 08:33 AM

I agree. I'd remove a little metal, grab a light and magnifying glass and look it over for cracks,make sure the pin still fits smoothly and put it back together. Might be a good time to check ring gaps if you didn't the first time. Then if the head gasket still looks reasonable, spray it with hylomar, or at the very least, copper coat, and reassemble it.

The take lots of videos of you doing wheelies and such so we can all watch and go "Ooooh and Ahhh"! Lol

bogieboy · 05-05-2021, 08:58 AM

didnt have time to post this when i typed my last reply...LOL you would be amazed what will run and stay together for years.... i have a Stihl BR600 backpack blower that came to me completely seized up from running on straight gas... i pounded the piston out, slapped a new one one (the old piston was too galled up from the seizure) and after a light honing of the bore to clean the aluminum off the walls of the nikasil bore, i freakin sent it, knowing it may blow, that was 3 years ago, and i have run about 10 gallons of premix thru it since... i figure if it blows, i am out the $30 piston... if it runs, i have a $600 blower for $30....

**JerryHawk250** · 05-05-2021, 09:28 AM

I agree with TxTaoRider and bogieboy on this. From looking at the pictures you post it doesn't look like any real damage was done. I've reused head gaskets many times on personal projects because I couldn't get a new one right away. Never had any issues.

Years ago my brother-in-law had a small mechanic shop that I would work at when this were slow for me. I would go through the pile of small outboard engines and would use all the good parts to build working engines. We would sell these engines to local commercial fishermen for the fraction of the price of a new engine. These motors were used daily and would last them 1 to 2 years. About the same as a new engine that wouldn't of been warranted anyway because of commercial use. When they did finally blew they would drop of the blown engine off and buy another. Those guys were super happy and always returned.

China Rider 27 · 05-05-2021, 10:09 AM

And GPX moto is providing you with a new big bore kit?

grumpyunk · 05-05-2021, 10:50 AM

Charles ... The piston wrist pin boss did not touch the crank throw shown in the picture a few posts above your reply.(first image in post #53) The boss would have impacted 180 off, when the counterweights were closest to the piston and the connecting rod journal down all the way. The piston would be at its closest position relative to the crank at BDC.
The crank throw area shown does have machining marks, but they are not from impacting the wrist pin area, obviously, as they are viewable with the piston as far away as possible. The collision area must have the weights as close as possible, or there would be not contact. The piston must be removed to see the area, or at a position to see past.
The vendor should replace the complete kit. I doubt the connecting rod has sustained any significant damage from stress. Seeing the potential contact area on the crankshaft would be interesting. I suspect more than scratches, but not significant gouging and scoring. I would have no problem using some copper coat on the head gasket, or alluminum paint as I have heard it works pretty well. My personal preference is for composition head gaskets even though they reduce the compression ration a bit. If you are good with snips and have hole punches, you could use a thin sheet of Cu.
tom
tom

ChopperCharles · 05-05-2021, 12:44 PM

You're right, here's the pic you're looking for.

The blue is machinists' layout fluid. You can see the scuffs/scrapes from teh bottom of the piston, and blue came off on the piston too.

The vendor should indeed replace the complete kit. That's what I want. I could make it work with just a new headgasket... but I shouldn't have to. Not for $200.

I'm not going to reuse a head gasket. I want to put 50k miles on this bike, and I don't want a head gasket failure on some remote trail a thousand miles from home. Not gonna risk that.

I can buy an individual 82mm headgasket from aliexpress... with a delivery date in mid june. So yeah, either GPX Moto sends me a complete replacement kit, or they give me my money back and I return it.

GPX Moto doesn't currently have kits in stock. They've ordered some, but gary is going to find out how long it will be before they arrive and get back to me today with that information.

I'm not really hopeful. Actually, I'm expecting bad news, and so I've already ordered all the parts I need from CSC to return the bike to stock. (A whopping $34).

This fiasco has already caused me to miss two events that I wanted to ride my RX3 to. I'm not willing to miss any more, even for more power.

Charles.

grumpyunk · 05-06-2021, 01:15 PM

You have contact at the very lower edge of the piston skirt, not the wrist pin boss, perhaps one side of the boss, but not both.
I'm a 'put it back together' kind. Not going to the moon, as some say, just ridin' around on dirt.
I have not seen a head gasket go on any of these air-cooled jewels. Only the shrouded, fan-cooled scooter types, when some 'I know better' wizard did an upgrade and decided those shrouds were not needed... Idiot. And the head gasket was not pretty(thin sheet steel type), but even then had not blown. Were it me, I'd get out the file, and shave a couple thousandths on the 'arc' of the skirt. The piston skirt bottom does have an arc that more or less conforms to the shape of the counterweight, right? I'd inspect the top of the cylinder and the bottom of the head, and just put it back together. I realize I am not the one to be stuck in the middle of Dirt Valley, but the odds of that are just so low as to be something that would soon trickle down to the 'never mind' level of concern. I expect these machines have been so over-abused in the wilds of the SE Asia that they have had head gaskets made of unfolded rain gutter sheet metal, pre-painted already. Said gasket working just as well as the 4-cent gasket you will (eventually) get from aliexpress. The speed of 'flats' coming is a lot better than box material. Expected date is way exaggerated for flats(envelope) as they just are dropped into the mail and don't seem to go through all the 'sorting centers' that boxes endure.
You could trim the piston and PBT with a painted gasket and know if you want to keep going down that path(as a test), or will be happy enough without this performance enhancement. If your vendor gives the OK to diddle with the piston for clearance, that is.
These engines for the most part are not very demanding as far as peak cylinder pressure and the need for perfect fitting head gaskets. They are closer to lawn mower engines and are quite forgiving.
Did you put blue on both wrist pin bosses? If so, was it scraped on both?
tom

05-04-2021, 11:19 AM	#61
grumpyunk Join Date: Jul 2018 Location: nw of atlanta Posts: 169	Are the counterweights on the crankshaft colliding with the wrist pin boss? If that's the case, the parts were either incorrectly machined or not designed to fit. Out of the box. No thicker head or base gasket would have any effect. No assembly technique would change the dimensions machined into the parts. Question is why does it seem to be quiet until rpms are increased, or did I hear it wrong? Can you put up a picture of the counterweights? Would be interesting to see the contact pattern. tom __________________ vertical and above ground - my daily goal
	0

05-05-2021, 08:33 AM	#69
TxTaoRider Join Date: Oct 2020 Location: Flower Mound Texas Posts: 904	I agree. I'd remove a little metal, grab a light and magnifying glass and look it over for cracks,make sure the pin still fits smoothly and put it back together. Might be a good time to check ring gaps if you didn't the first time. Then if the head gasket still looks reasonable, spray it with hylomar, or at the very least, copper coat, and reassemble it. The take lots of videos of you doing wheelies and such so we can all watch and go "Ooooh and Ahhh"! Lol __________________ 2021 Tao Tbr7 - "Lucille" Mods so far- Brozz swingarm, 21" front rim (Bridgestone Tw302 rear/Dunlop D606 front tires), Digital gauge cluster, pz30b pumper carb, after market hand guards, aftermarket brake and clutch levers, round fold away mirrors, Fly handlebars shortened slightly, 13t front sprocket 2009 Q-link Legacy 250 1982 Suzuki GS1100ES - "Jolene"
	2

05-05-2021, 09:28 AM	#71
JerryHawk250 Moderator Join Date: Oct 2016 Location: Houma, La. Posts: 11,739	I agree with TxTaoRider and bogieboy on this. From looking at the pictures you post it doesn't look like any real damage was done. I've reused head gaskets many times on personal projects because I couldn't get a new one right away. Never had any issues. Years ago my brother-in-law had a small mechanic shop that I would work at when this were slow for me. I would go through the pile of small outboard engines and would use all the good parts to build working engines. We would sell these engines to local commercial fishermen for the fraction of the price of a new engine. These motors were used daily and would last them 1 to 2 years. About the same as a new engine that wouldn't of been warranted anyway because of commercial use. When they did finally blew they would drop of the blown engine off and buy another. Those guys were super happy and always returned. __________________ 2024 Linhai 300 ATV 4x4 2023 Lifan Lycan 250 Chopper 2023 Venom Evader 2022 Lifan KPX250 2020 Kawasaki Vulcan S (Sold) 2004 Honda ST 1300 2016 Black Hawk 250 (sold) Keihin PE30 carb,125 main,38 slow.Pod filter,ported & decked head 10:1 CR,Direct Ignition Coil,15/40Sprockets,NGK DPR8EIX-9,De-Cat,Dual Oil Cooler,Digital Cluster 2016 Cazador180 XL 2014 Coolster150 JerryHawk250.com My YouTube Channel
	0

05-05-2021, 10:50 AM	#73
grumpyunk Join Date: Jul 2018 Location: nw of atlanta Posts: 169	Charles ... The piston wrist pin boss did not touch the crank throw shown in the picture a few posts above your reply.(first image in post #53) The boss would have impacted 180 off, when the counterweights were closest to the piston and the connecting rod journal down all the way. The piston would be at its closest position relative to the crank at BDC. The crank throw area shown does have machining marks, but they are not from impacting the wrist pin area, obviously, as they are viewable with the piston as far away as possible. The collision area must have the weights as close as possible, or there would be not contact. The piston must be removed to see the area, or at a position to see past. The vendor should replace the complete kit. I doubt the connecting rod has sustained any significant damage from stress. Seeing the potential contact area on the crankshaft would be interesting. I suspect more than scratches, but not significant gouging and scoring. I would have no problem using some copper coat on the head gasket, or alluminum paint as I have heard it works pretty well. My personal preference is for composition head gaskets even though they reduce the compression ration a bit. If you are good with snips and have hole punches, you could use a thin sheet of Cu. tom tom __________________ vertical and above ground - my daily goal
	0

05-06-2021, 01:15 PM	#75
grumpyunk Join Date: Jul 2018 Location: nw of atlanta Posts: 169	You have contact at the very lower edge of the piston skirt, not the wrist pin boss, perhaps one side of the boss, but not both. I'm a 'put it back together' kind. Not going to the moon, as some say, just ridin' around on dirt. I have not seen a head gasket go on any of these air-cooled jewels. Only the shrouded, fan-cooled scooter types, when some 'I know better' wizard did an upgrade and decided those shrouds were not needed... Idiot. And the head gasket was not pretty(thin sheet steel type), but even then had not blown. Were it me, I'd get out the file, and shave a couple thousandths on the 'arc' of the skirt. The piston skirt bottom does have an arc that more or less conforms to the shape of the counterweight, right? I'd inspect the top of the cylinder and the bottom of the head, and just put it back together. I realize I am not the one to be stuck in the middle of Dirt Valley, but the odds of that are just so low as to be something that would soon trickle down to the 'never mind' level of concern. I expect these machines have been so over-abused in the wilds of the SE Asia that they have had head gaskets made of unfolded rain gutter sheet metal, pre-painted already. Said gasket working just as well as the 4-cent gasket you will (eventually) get from aliexpress. The speed of 'flats' coming is a lot better than box material. Expected date is way exaggerated for flats(envelope) as they just are dropped into the mail and don't seem to go through all the 'sorting centers' that boxes endure. You could trim the piston and PBT with a painted gasket and know if you want to keep going down that path(as a test), or will be happy enough without this performance enhancement. If your vendor gives the OK to diddle with the piston for clearance, that is. These engines for the most part are not very demanding as far as peak cylinder pressure and the need for perfect fitting head gaskets. They are closer to lawn mower engines and are quite forgiving. Did you put blue on both wrist pin bosses? If so, was it scraped on both? tom __________________ vertical and above ground - my daily goal
	0

05-04-2021, 11:27 AM	#62
ChopperCharles Join Date: Feb 2018 Location: RDU, NC Posts: 683	I will use blue machining layout fluid on both surfaces and refit the piston so you can see the contact. So, it still made noise at idle. More than I thought it should. The reason it made MORE noise as RPM increased is likely the loads increase and the tolerances tighten as piston speed increases, and instead of slowly rubbing by the counterweights it was now slamming into them at speed. Thermal expansion is also a probable reason. It also explains why the noise was two times the speed of the exhaust note. 4 stroke engine, piston moves up and down twice for each power pulse. And yes, that's exactly what's happening. The wrist pin boss is not properly machined, and thus incorrectly machined out of the box. Pic of counterweights is above. Charles.
	0

05-04-2021, 11:41 AM	#63
ChopperCharles Join Date: Feb 2018 Location: RDU, NC Posts: 683	So I bought my kit from GPX Moto, and it's the RTC kit. The RTC kit is also on AliExpress, and if you look at the pics on AliExpress the wrist pin boss has a lot more machining. So it appears I got a defective big bore kit. Charles.
	1

05-04-2021, 06:49 PM	#65
ChopperCharles Join Date: Feb 2018 Location: RDU, NC Posts: 683	Ugh, unfortunately GPXMoto is out of big bore kits right now. Waiting on news when they'll get more. If they're not coming in soon I'm going to put the original piston back in. Charles.
	1

05-04-2021, 10:13 PM	#66
bogieboy Join Date: May 2013 Location: finger lakes NY Posts: 2,062	My personal opinion, which may not be worth much, is just grind down the bosses til you have clearance and run it... if it was going to stress the rod or anything, it likely would not have even turned over completely the first time you went to fire it... i would take about 5thou off that piston's bosses and run it....
	0

05-04-2021, 10:33 PM	#67
ChopperCharles Join Date: Feb 2018 Location: RDU, NC Posts: 683	That’s a great idea except I still have no source for a replacement head gasket. I am worried about stress fractures in the piston. Charles.
	1

05-05-2021, 07:39 AM	#68
bogieboy Join Date: May 2013 Location: finger lakes NY Posts: 2,062	I wouldnt worry about stress fractures, and i would reuse the head gasket and ship it..... maybe think about getting a piston and headgasket down the road as a spare, but i would bet they will be fine....
	3

05-05-2021, 08:58 AM	#70
bogieboy Join Date: May 2013 Location: finger lakes NY Posts: 2,062	didnt have time to post this when i typed my last reply...LOL you would be amazed what will run and stay together for years.... i have a Stihl BR600 backpack blower that came to me completely seized up from running on straight gas... i pounded the piston out, slapped a new one one (the old piston was too galled up from the seizure) and after a light honing of the bore to clean the aluminum off the walls of the nikasil bore, i freakin sent it, knowing it may blow, that was 3 years ago, and i have run about 10 gallons of premix thru it since... i figure if it blows, i am out the $30 piston... if it runs, i have a $600 blower for $30....
	1

05-05-2021, 10:09 AM	#72
China Rider 27 Join Date: Dec 2018 Location: PNW Posts: 984	And GPX moto is providing you with a new big bore kit?
	0

05-05-2021, 12:44 PM	#74
ChopperCharles Join Date: Feb 2018 Location: RDU, NC Posts: 683	You're right, here's the pic you're looking for. The blue is machinists' layout fluid. You can see the scuffs/scrapes from teh bottom of the piston, and blue came off on the piston too. The vendor should indeed replace the complete kit. That's what I want. I could make it work with just a new headgasket... but I shouldn't have to. Not for $200. I'm not going to reuse a head gasket. I want to put 50k miles on this bike, and I don't want a head gasket failure on some remote trail a thousand miles from home. Not gonna risk that. I can buy an individual 82mm headgasket from aliexpress... with a delivery date in mid june. So yeah, either GPX Moto sends me a complete replacement kit, or they give me my money back and I return it. GPX Moto doesn't currently have kits in stock. They've ordered some, but gary is going to find out how long it will be before they arrive and get back to me today with that information. I'm not really hopeful. Actually, I'm expecting bad news, and so I've already ordered all the parts I need from CSC to return the bike to stock. (A whopping $34). This fiasco has already caused me to miss two events that I wanted to ride my RX3 to. I'm not willing to miss any more, even for more power. Charles.
	0