Okay so a few months ago i rebuilt my blaster top end. I had the cylinder bored to 67.5 and hones and chamfered. I put in a new wrist pin bearing, and a new piston kit from pro x. My bike has stock jetting and everything stock except it obviously is bored to 67.5, it has tors and parking brake delete, it has vitos reeds and it has oil injection delete. Anyways, the top end lasted less than 5 hours before it started to act weird and was getting hung up and bogging when full throttle. I tore the top end off, and my piston and cylinder had these nasty looking scuff marks on the sides. I took the cylinder to a machine shop and had them hone out the wear marks, and they said it was still exactly 67.5, so i ordered a wiseco 67.5 piston, and again rebuilt the top end. (No up and down play in the crank by the way). I switched from cheap 2 cycle oil from auto parts store to klotz benol 32:1 with 93 octane. I did my 3 heat cycles, and when i ride it, it runs good in first gear and neutral but in second and 3rd, it bogs and gets hung up. What could it be? I did a leak down test and no leaks.
Problems after rebuild
- Thread starter Conner Jones
- Start date
What was the piston to cylinder clearance after the rebuild ?
measured like this with dial calipers, or jump to 7 minutes into the video use feeler gauges .......
https://www.blasterforum.com/threads/how-to-measure-your-cylinder-diy.25767/
the machine shop should have had the exact piston to be used in their hands before bore/honing the cylinder to the correct clearance for that exact piston, the piston usually supplies the recommended clearance in the instructions included in the box.
not all are created equal ... same pistons could be a couple thousands difference, different brands supply different sizes, cast requires less clearance than forged pistons, some under size the piston for clearance (built in), some don't, etc.
Sadly, if you slapped a 67.5 piston in a 67.5 hole, as the piston is heating up and expanding, it doesn't have the needed clearance for that pistons heat expansion, and is seizing in the bore.
No way that shop honed out a cylinder and it remained the same size it was.
you need to find a new shop.
most of us use kenoconnorracing.com
measured like this with dial calipers, or jump to 7 minutes into the video use feeler gauges .......
https://www.blasterforum.com/threads/how-to-measure-your-cylinder-diy.25767/
the machine shop should have had the exact piston to be used in their hands before bore/honing the cylinder to the correct clearance for that exact piston, the piston usually supplies the recommended clearance in the instructions included in the box.
not all are created equal ... same pistons could be a couple thousands difference, different brands supply different sizes, cast requires less clearance than forged pistons, some under size the piston for clearance (built in), some don't, etc.
Sadly, if you slapped a 67.5 piston in a 67.5 hole, as the piston is heating up and expanding, it doesn't have the needed clearance for that pistons heat expansion, and is seizing in the bore.
No way that shop honed out a cylinder and it remained the same size it was.
you need to find a new shop.
most of us use kenoconnorracing.com
On the wiseco piston box it says its for a 2.6575 inch bore, which is exactly 67.5mm. The machine shop measured it in front of me and it was exactly 67.5mm, and the piston box says clearance of .051mm so shouldn't the wiseco piston be 67.551? Before I did this last rebuild, I actually already purchased a wossner 68mm piston and took it to the shop to have the guy bore the cylinder out to 68 but he looked at it and told me that he could hone out the scoring, and that I should return the 68mm piston and buy another 67.5 piston. So thats what I did. I realized now that I never checked the ring end gap. Could that be a problem?
The piston needs to smaller than the bore according to the manufacturers specs
Like awk said cast pistons take a tighter clearance than. A forged piston which expands more. You should always check ring Gap
Does the engine turn over freely with plug out?
Im sorry, I added the clearance instead of subtracting it. What i was trying to say was, shouldnt the wiseco piston already be 67.449mm, since the box says its for a 67.5mm bore? That would give it the .051mm clearance it says on the box. And yes the engine turns over fine with the spark plug out. It has good compression with the plug in. I just dont get why it runs fine in first gear with lots of power, but then in second and third, it sounds like the motor is holding back.
So your clearance issues are fixed? Piston installed correctly. You did a leakdown test after assembly? Compression is at? Just asking because these. Are ussual checks after a rebuild.What's your plug look like? If oil deleted.is orfice capped off where oil feed line went on carb
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Tommorow i am going to buy feeler gauges to measure ring end gap and also piston cylinder clearance. As far as i know, thr clearance should be correct according to the shop but im going to use feeler gauge to make sure. I did a leak down test before I did my heat cycles and no leaks. I will do a compression test tomorrow after i check clearance and re assemble engine. I did install the piston correctly, with the arrow to the exhaust, and with circlips gap up. My carb oil injection hose is blocked off, and there is a block off plate under the oil pump cover. I'm just nervous because this is my second rebuild and I dont want it to fail like the last one did so quickly.
I checked the ring gap and both rings are between .013 and .014 inches. 2.657 inch bore x .005 inch equals .0133 inch minimum ring end gap so i think im good with that. I used the ken oconnor video for cylinder gap using feeler gauges and I got between .002 and .0025 inch clearance. The piston box says .002 inch clearance, so do you guys think im good? I guess I'm just going to buy a new carburetor and maybe reeds and hope that makes it run right. I dont really know what else to do. Is there anything I need to check for the bottom end? I already checked for up and down play and theres none. Is it possible that something went bad in my transmission and makes it bog in any other gear than first? I attatched pictures of the cylinder and piston. They look fine to me.
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Okay so ive got everythinf back together and i think i have it figured out. When i was rebuilding the top end, i noticed that the washer under the main jet was missing, so I bought one and installed it. With the washer in, the engine womt rev out in ghe higher gears. Then i took the main jet washer out, and it seems to be running decent now. Does this mean i need to change my needle position or something so i can put the washer on and still have it run correctly? Right now the needle is in middle position.
Yes i used the piston pin and clips that came with the new wiseco piston for 67.5 bore. I used a brand new wiseco wirst pin bearing. I took my clinder to the shop and they honed it and said it was exactly 67.5 so I bought the wiseco piston for a 67.5 bore. And yes the cylinder was already chambered before I had them hone it. My clearance should be fine because as i mentioned in my previous posts, i checked the clearance with a feeler gauge and it was between .002 and .0025 inch clearance and wiseco recommends .002 inch clearance. And ring gaps were within spec. Im running 93 octane pump gas with klotz benol 32:1. From my understanding, removing the washer is like raising the needle clip 2 positions (which is leaning it out). The clip was in the middle position, so i guess by removing the washer, it would be like it was in the top position. I dont get why my quad must need that lean of a needle position to rev out.
Ive never used a different needle in the time that I have owned it. The needle has 5j22 stamped on it, so does that mean its stock?
