Need help with topend rebuild

bullman926

New Member
Dec 23, 2013
15
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North East GA
I tried to search the forum for this but had no luck. I'm rebuilding the top end on my 2000 Blaster and I'm moving it up to the 67mm Wiseco Piston. My question is do I need to buy aftermarket jets for the carb to make up for the larger piston or can I tune the carb with the factory jets to make up for it? Any help would be appreciated. Thank you and yes I know I'm a noob.
 
No need to change jets for only the overbore.

If you alter anything else it may be a different story.

After rebuild make sure you leak test it to see if it is airtight before you heat cycle it.
 
no jetting will be needed, the bore size doesent affect jetting, give your top end to a good shop to rebore it, they will need the piston in hand before boring it, i advise going wiseco. you will likely need to readjust idle and the air screw after the rebuild. why did it blow up? if the piston is shattered you will need to crack the cases if there is alot of crap in there.
 
That's why its helpful for the shop that's boring your cylinder to have the piston before hand. That way they'll know exactly what the piston to cylinder clearance will be. Some reputable shops will know how much clearance is needed depending on the brand of piston without actually having the piston. For instance when I had my cylinder bored I told the guy I would be going with a wiseco prolite piston, he said he was familiar with the exact sizes wiseco ran and what the piston to cylinder clearance should be so I could wait to order the piston until after we knew how much we had to take off.
 
I appreciate all the help guys! Yes I ordered the wiseco topend rebuild kit for it. I'm not sure why it blew up as when I purchased it I was told it just had weak spark. I replaced the plug and stator and got hot spark but still it wouldn't crank. Pulled out the compression tester and it was at 35#'s. When I pulled the topend the piston wasn't shattered but the rings were cooked. The piston did have scarring on it as did the cylinder wall. I'm a noob at small engines and have never even "Cracked a case" before. I surely don't want to put a fresh topend on it just to have something else go wrong. I do have a good shop that is waiting for my piston to arrive before he bores it though. I'm not sure if I should crack the case or not by looking at the piston/rings but if it was necessary I may give it a shot. I just don't know that my lack of experience would leave me better or worst off...

Also I plan to install an aftermarket exhaust. Would that make jetting the carb necessary?
 
Why are you going up to 67mm? Forgive me if I'm wrong but from your question I assume you haven't had a lot of experience with engine building. Be sure the engine shop knows 2 strokes, 2 stroke cylinder requires the ports to be chamfered after the final bore and hone is finished. Luckily I procrastinate and had joined here before I ever put that engine back together (I actually still haven't put it back together but that's a different story), learning that chamfering HAS to be done. I'm sure that the ports would have snagged a ring had I put the engine back together as it came from the shop. If you are lucky enough to have a local shop that you know knows what they are doing within a 2 stroke engine, great......if not consider talk to KOR. The cost to have KOR to do my Blaster was about $50 more than I spent on the CR250, but with that $50 extra I got all OEM gaskets for the Blaster vs aftermarket for the CR, I used Pro Lite piston kits in both. I'm all about saving money but for me getting the quality work from KOR was worth 3 times the extra cost compared to the incomplete work I got locally.
 
If the piston is still in tact and there are no chunks or debree missing from the piston, rings or head than you probably don't need to split the cases which is obviously good news ... Make sure you leak test after the top end rebuild as advised to ensure everything is air tight. Anything that you instal that increases air flow will require re-jetting, you should use the "search" function and read up on plug chopping before installing any after market parts. Also read up on proper "break in" procedure for after the rebuild. I paid under $50 to have my cylinder bored and honed by a local reputable shop so don't let your local shop over charge you ... Good luck with everything and don't hesitate to use the forum and ask for help ... That's what were all here for !
 
Why are you going up to 67mm? Forgive me if I'm wrong but from your question I assume you haven't had a lot of experience with engine building. Be sure the engine shop knows 2 strokes, 2 stroke cylinder requires the ports to be chamfered after the final bore and hone is finished. Luckily I procrastinate and had joined here before I ever put that engine back together (I actually still haven't put it back together but that's a different story), learning that chamfering HAS to be done. I'm sure that the ports would have snagged a ring had I put the engine back together as it came from the shop. If you are lucky enough to have a local shop that you know knows what they are doing within a 2 stroke engine, great......if not consider talk to KOR. The cost to have KOR to do my Blaster was about $50 more than I spent on the CR250, but with that $50 extra I got all OEM gaskets for the Blaster vs aftermarket for the CR, I used Pro Lite piston kits in both. I'm all about saving money but for me getting the quality work from KOR was worth 3 times the extra cost compared to the incomplete work I got locally.

The reason I went with 67mm was because the guy boring/honing my cylinder told me that I needed to go a size bigger with the piston. Of coarse me not knowing much about small engines I search that 66mm was the stock size and assume the next size up was 67mm. Now that I have done a little more research I see otherwise. But it's too late now because I've already purchased the 67mm kit. I bought the wiseco kit with the piston rings wrist pin bearing and all topend gaskets. But what do you mean by Chamfering? Are you referring to the ports in the cylinder?
 
But what do you mean by Chamfering? Are you referring to the ports in the cylinder?

On a 2 stroke the air/fuel mix and exhaust come into and out of the cylinder through ports (intake, transfer and exhaust ports) cut through the cylinder walls, where 4 strokes move the mix through the valves in the cylinder head. The piston moves up and down over these holes and the rings will slightly expand into these openings. Chamfering is the sight bevel cut at the shape edge of the ports to allow the rings to recompress into the ring groove of the piston instead of snagging and ripping them out or breaking the edge of the ring off.
I was able to do the chamfering on my CR cylinder using the cylinder that KOR had done for me as a guide, though not as consistent as the KOR cylinder I'm sure it will be OK. I probably spend 4 hours doing it (I'm guess a pro does it in minutes) and that was with professional porting tools, not a Dremal. I sure some others can explain this better and probably provide pictures.
 
On a 2 stroke the air/fuel mix and exhaust come into and out of the cylinder through ports (intake, transfer and exhaust ports) cut through the cylinder walls, where 4 strokes move the mix through the valves in the cylinder head. The piston moves up and down over these holes and the rings will slightly expand into these openings. Chamfering is the sight bevel cut at the shape edge of the ports to allow the rings to recompress into the ring groove of the piston instead of snagging and ripping them out or breaking the edge of the ring off.
I was able to do the chamfering on my CR cylinder using the cylinder that KOR had done for me as a guide, though not as consistent as the KOR cylinder I'm sure it will be OK. I probably spend 4 hours doing it (I'm guess a pro does it in minutes) and that was with professional porting tools, not a Dremal. I sure some others can explain this better and probably provide pictures.

I see now. I had to look up a youtube video of how exactly a two stroke works to clarify but I see what you mean now. Well the guy that is boring my cylinder is an older gentlemen who has done the work on my wifes grandparents atv's for quite some time so I'm assuming he knows all about two strokes. I will however run this by him when I take him the piston on Saturday to be sure. Thank you again for the advice. Now I am stumped on the plug chopping. I'm just a little confused about how to do it and what it does, what i am looking for and such things. I searched the forum but only found people who were having problems and whose photo's had been deleted.
 
Tech Blaaster usually posts his How to Plug Chop and leak test instructions when asked for them. Hopefully he will just post them to your thread after reading this :)
 
If you are having problems finding stuff with the forum search you can use Google to search the site by adding site:www.blasterforum.com after the keywords. The results will only be from the forum. For me it makes finding information much easier/faster.
 
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Done at the drop of a hat.

Before you make the plug chop run it is important that the float level is correct, the idle is set correctly and there are no air leaks in the system, otherwise the smoke ring may lie about the AFR.

WHEN ALL OF THE ABOVE ARE CORRECT PROCEED WITH THE FOLLOWING.

Warm up motor to operating temp.

Fit new B8ES plug, ride WOT through the gears and hold WOT in 5th or 6th gear for 10 seconds, or as long as you can safely.

Switch off the motor and pull in the clutch, apply brakes to come to a stop quickly.

Take the plug out and replace the old one for the ride home.

Carefully cut the threaded end off the plug to expose the insulator.

There should be a smoke ring of a cardboard or biscuit colour around the insulator.

If it is non existant or a very light colour, you are lean and require a larger main jet.

If it is a lot darker you are rich and may go down a size in main.

I prefer to run a little on the darker side, I may loose a little power but it is worth it for the peace of mind that I won't need a rebuild so soon.

http://www.blasterforum.com/do-yourself-20/how-plug-chop-38674/

http://www.blasterforum.com/engine-13/plug-chop-how-vid-48226/

This is a good to go plug.

2wr2fwo.jpg



This one is a little rich, but I would run it, I like to be on the safe side.

plug152mainmediumoi2.jpg


You have to get up a reasonable speed so that you can get the motor to pull strongly.

Then hold it Wide Open Throttle (WOT) for 10 secs or as long as you can.

The idea is not to get speed but to make it pull strong at full throttle to get onto the main jet circuit.

I find I can safely do it on a short run by applying the brakes some.

If you have not enough room you can use 4th or 5th gear with good results.

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