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Hello everyone,

I just found this forum and thought that some of the folks here may be able to help me, or maybe not. Last week I picked up what looked like a brand new Craftsman 51cc backpack blower. I should have known better because I quickly found out that the piston was completely scored up and it had low compression (somewhere between 90-110 psi, which I think is too low to run on something like this).

I ended up pulling it all apart and tried to sand it somewhat and tried to unstick the piston rings which were stuck in the piston. Once I got it all back together I thought I had a small chance because I got it up to about 155 psi. I attempted to start it and got it to run very briefly before the compression dropped down again and it stopped. I think I can get by with just a new piston and probably a set of rings for this thing but I don't want to spend a ton of money on it do to the circumstances.

The problem for me was upon looking it up, I see that MTD only offers the entire short block assembly and I don't think I need the cylinder or crankshaft along with the rest of the parts that come with it. The cylinder is surprisingly in pretty nice shape, the piston took the brunt of it. The emissions tag was from 2022 so whoever bought it probably ran with straight gas. To provide more context here is the parts diagram I was referencing:


The Mtd part number for the short block is 753-11138. I saw this blower made under a couple different names too like Troy-bilt and I think I even saw it on Ebay and Amazon as something else. Just wondering if anyone has any info on getting the parts individually or if I just should move on. Thanks for your time.

If you Google the PN you find it for less than the Partstree price as the list price is $78.27 at my distributor.

Red Dog will ship for free but the shipping is in the price.

https://www.reddogsupplies.com/products/mtd-753-11138-shblk-asm​

But yes if the piston is heavy scored then you need the cylinder too. And anything around 100 psi is too low for a two cycle to run on normally although I have a couple that ran at 95 psi. And you do need to find out why PNC got scored in the first place or the new one will do the same in short order.

mechanic mark said:

51cc 2-Cycle Backpack Gas Leaf Blower (BP510)

Tackle your debris clearing needs with the power of the CRAFTSMAN® BP510 Gas Backpack Leaf Blower. Equipped with a 51 cc full-crank engine, clearing leaves and yard debris is a breeze with air volume and air speed up to 600 CFM/220 MPH. The BP510 is designed with comfort in mind, with an extra...

www.craftsman.com

https://www.jackssmallengines.com/equipment/craftsman/leaf-blower/pistons-and-rings

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Hey thanks StarTech and Mark for your replies. I think it was run with straight gas right away because it looks practically brand new. I will check out the short block maybe, my other question was that it has a 2-ring set up. Are these MTD pistons the same diameter or do they vary based on model? I also apologize for my ignorance on this as I am a DIY guy with a bunch of tools and that's about it. Thank you

Pistons are an unknown on these due to fact that MTD only provides a short block. Years ago we could just piston and cylinders but they have change their parts sells to reduce warehouse space usage.

When it comes 2 cycles they are completely different beast than 4 cycles. Not bad to work on if we could only get the parts we need instead being force into things like complete short blocks. With short blocks they drive the repair up to a point no one other DIYers can do the repairs as we must charge for labor. Even with limiting nearly all the handheld repairs to one hour billable labor even though it may take up to hours to do it is still too high as most owners are not willing to spend the funds on the repairs. They think because it is small and was cheap to buy it should be just as cheap to repair when it is not.

StarTech said:

Pistons are an unknown on these due to fact that MTD only provides a short block. Years ago we could just piston and cylinders but they have change their parts sells to reduce warehouse space usage.

When it comes 2 cycles they are completely different beast than 4 cycles. Not bad to work on if we could only get the parts we need instead being force into things like complete short blocks. With short blocks they drive the repair up to a point no one other DIYers can do the repairs as we must charge for labor. Even with limiting nearly all the handheld repairs to one hour billable labor even though it may take up to hours to do it is still too high as most owners are not willing to spend the funds on the repairs. They think because it is small and was cheap to buy it should be just as cheap to repair when it is not.

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And you have hit the head of the nail with the handheld stuff. Unless it is high end product handheld products due to cost of either labor or parts are not repairable. Like $124.95 for an ignition module on a $169.00 blower. Or a few years ago the rear tine chain drive transmission for the MTD tiller was $649 for a tiller that sold new retail for $599

I agree with you guys, it is crazy how expensive this stuff is. I guess that's why most people don't bother to work on the 2-cycle stuff other than high end models like husky or Stihl, Echo, etc. Just not cost effective from a mechanics standpoint with diagnostic and labor times. I think I may venture to buy the short block and hopefully I can break even on it anyways. It will give me a chance to learn more too. Thanks for your time.

Even the high end stuff is certain cases isn't even work fixing. You can drop $400+ into a Stihl saw that cost $500 new with a top end cylinder/piston kit and other goodies that are needed.

Measure the piston length , height & diameter plus the pin hole diameter & the middle of the pin hole to top of the piston crown height
Also the ring width
There are probably 2000 Chain saw, line trimmer or other hand held small 2 stroke pistons that can fit.
Most of the Chinese aftermarket parts companies sell just pistons
If you send them the essential piston dimensions they can usually find a stock piston that will fit
When you get it weight it carefully as it must be the same weight as the original or the engine will self destruct

bertsmobile1 said:

Measure the piston length , height & diameter plus the pin hole diameter & the middle of the pin hole to top of the piston crown height
Also the ring width
There are probably 2000 Chain saw, line trimmer or other hand held small 2 stroke pistons that can fit.
Most of the Chinese aftermarket parts companies sell just pistons
If you send them the essential piston dimensions they can usually find a stock piston that will fit
When you get it weight it carefully as it must be the same weight as the original or the engine will self destruct

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Many of the larger shops around here will only work on the brand of 2-stroke handheld equipment they sell, ie: Stihl, Husqvarna, Echo, Redmax.

Being a small independent shop I would work on about everything to make ends meet. But I do draw the line at el cheapo equipment as it is just a waste of my time to even look at it as most repairs are more then they cost new. Many of 4 cycle handhelds usually now requires short blocks to even repair them. And few years ago I was getting unit where to even remove the piston you had to disassemble the crankshaft.

Another reason why I am buying more & more stuff from EMAS in China ( who supply to Rotary, Stens, Prime Line as well as OEM suppliers to MTD , Husqvarna & Stihl + a mile of Chinese brands

Last year I rebuilt a pretty beat up small tiller I got from the trash. I had picked it up for some parts but thought I could see if it would work at all. Anyway, I ended up putting in a new piston ring, its a cheapo with just one but I got it going well enough to do my small raised bed gardens. I looked on EBay for some sort of parts person and found a couple of piston rings for a few dollars with shipping. If you got the time and energy to expend, you might be able to find what will work or if you are lucky, some old exact parts that are useable. I think its more of a time and how much eneergy is worth the trouble energy issue than actually being able to make it work.

if it ran with no oil, you may have bearing issues too.

To give some closure to the thread, I ended up getting the short block at a lower price and installed it tonight. The blower runs good now. Thanks for your time everyone!

Thank you for that .
Very few come back and a closed successful thread is very worthwhile .

ILENGINE said:

Even the high end stuff is certain cases isn't even work fixing. You can drop $400+ into a Stihl saw that cost $500 new with a top end cylinder/piston kit and other goodies that are needed.

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i bought a cylinder and piston with the rings kit for $50.00 and repaired a Sthil 026 chainsaw, and i'm still usingit 4 years later.