Piston Too Tight In Bore

[markus]

Massacre, refer to page 98 in the L head shop manual that you can reference from small engine suppliers (linked up in the sticky threads in this section...page 98 will actually be page 102 if viewed in the PDF). Use columns 3 (for the late model HS50 and HSSK engines) and 4 (early HS50 and HSSK engines) Maybe print that page out and highlight the numbers shown in the "Bore", "Piston diameter Bottom of skirt" and "piston skirt clearance" sections

Now go back and measure everything again that way and see where your at on the numbers? Also, you weren't simply experiencing a bind somewhere were you when you put it together the first time? I had a deformed rod throw me for a loop once, shit happens. Have you bolted the cylinder shroud onto that block?...If so, you didn't use too long of a bolt and accidentally poke into the cylinder bore or anything like that???

If you do in fact have a .010 over piston assembly, It should be clearly marked on the top of the piston as such, the rings if it came with them, could be a crapshoot though unless it was a factory sealed box or from a new parts vendor.

 

[massacre]

Thanks for the guidance Markus

Rod is billet ARC roc, I built an engine with same basic specs (except for the piston size) and it runs great.
This one is tight throughout the travel with BB side cover bolted on and no cam. I removed the cam the eliminate that as part of the problem.
No cylinder shroud installed, no hole in block. But I know what you mean, there’s that little short bolt at the front that holds the tin on.

 

[massacre]

My piston does say .010 on the top
Rings were not in sealed package so are def suspect

 

[markus]

I yanked a box out today that had some HS50 parts in it and did some quick and dirty measurements with just a digital caliper for ya. There was one later small bore and some earlier large bore parts so I did one of each to compare. This is all stock sized lightly used parts (light hone on the blocks). Like I highlighted in the above post, the measurement is taken at the skirt not the top of piston, they do go smaller up top at the rings and very top which I imagine you may be trying to take the measurements from???

hopefully you can decipher my chicken scratch writing....I'm a lefty



Hopefully that may help?

 

[massacre]

Thanks Markus I really appreciate it

I was measuring pistons from top instead of the skirt. My bad

 

[massacre]

Your pic was easy to understand and informative. I printed that and the pdf
Can’t thank you enough

 

[markus]

No problem....hopefully you can get it figured out and working.

 

[massacre]

Thanks again Markus and everyone for your patience and guidance.

After measuring all 3 pistons at the skirt, I got 2.807, 2.808 for the stock pistons, and 2.813 for the 010” over piston.

The 2.795” piston is a thin ring Hs50 piston that I had, just checking to make sure I was measuring correctly.

I checked the box that the piston came in, part# was 34536, which is correct for .010 over Hs50 piston. So the piston is correct.

On the rings that I was using, I had about an 1/8” end gap. Way too much. Checked the number on the box the rings came in- part # 33568, which is correct for .010 over Hs50 piston rings.

I found another Tecumseh box with rings in it, same number 33568. This box had tissue paper in it, good sign lol
When I checked the end gap on these rings, boom- .008. Checked them all, same end gap.

So I reinstalled the piston, rod and crank, cam. Put the side cover on and put flywheel on loose but tight enough to spin over by hand. I am happy to report that the piston seems to be perfect in the bore now.

So I guess the box was correct, but the rings that came in that box were not correct. And as usual I started overthinking it and got a little worried there. Finding that second box of rings saved the day.

Now I can continue with this build, I had been stuck on this problem for months trying to figure it out.
Thanks again Markus and OldMiniBikes!

 

[massacre]

Thanks Del Ray I know you don’t like the “slug” piston and I can see why
I don’t spin my engines as high as you do so it seems to be doing ok for what I need it to do