Top end kits: NOS vs repos?

[PES+]

For the cylinders we used a snap gauge that was measured against the mics. The cylinders seemed uniform throughout with the mics we were using +/-0.0005.

We checked the pistons at the bottom of the skirt and near the crown in several places, in retrospect I should have taken some measurements mid-piston. As stated there was "taper" from skirt to crown but no out of round detected.

Our machinist at work checked the pin bores, I'll have to check on what type of mic he used, it was not a snap gauge. All the equipment in our machine shop is first rate (for the stated tolerances) although I'd have to check the brands.

Sorry no digital camera (yet) so can't provide any pics.


P.S.Our machinist got a chuckle when I directed him to a "hotsaw" website with a 500cc "bikesaw". He is a motor head too with lots of hotrod chevys, I think one has a big block "merlin" motor....

I asked for my own reference because there are quite a few different types of inside measurement anvils.

I can't imagine attempting using snap gauges with a .0005 mic even more so with small bores but what ever works.

Tolerances for 2 strokes in general and chainsaws in particular do not need to be very tight and conversely under really harsh conditions can cause aggravation.

I am still chuckling about Randy ebay rebuilding a Mac 101 and setting it up for 4 thou piston clearance as he stated on his auction.

I wish the buyer luck when he loads that motor hard and fast when hot on the track.

4 corner seize city.

 

[Lakeside53]

Snap gauges SUCK for repeatable and accurate measurements, and combine that with a 1/2 thou mic.. oh well.. Good try though.

Are you sure your mics are only 1/2 thou? Most decent mics (digital or not)also have a vernier on the barrel in 10ths.

Snap gauges were why I finally broke down and bought some real bore gauges....

 

[huskydave]

Snap gauges are designed for measuring high volumes of parts and are only as accurate as the person who set them.

 

[Lakeside53]

So true.. but they still suck (for me) when your spliting 1000ths. I still use them, but just for a rough measure.

 

[Tzed250]

I do not trust a telescoping gages for anything closer than .001".

This is a bore gage:

 

[Lakeside53]

ohhhh baby...:rockn: :rockn: :rockn:


Tools make collecting saws look cheap

 

[Goat]

I do not trust a telescoping gages for anything closer than .001".

That's being optimistic.

Quit messing around...throw that SOB on a CMM

 

[Mad Professor]

I do not trust a telescoping gages for anything closer than .001".

This is a bore gage:

Nice!! how accurate? Can it do fifty millionths or maybe ten millionths? For 0.0005" snap gauges are fine IF you know how to use them WITH a corresponding mic; average several measurements that agree, in fact that is how ANY measurement should be done........an average of several. A SINGLE measurement has little accuracy and NO precision. For a circle/cylinder measurements at several places along both the bore and axis where each intersect, all in replicate. What was the average? Thats's what you report....

The kind man who suggested to me 0.0005" tolerance had worked as a machinist where they measured 50 millionths clearance if needed and measured very close to a millionth (0.000001) tolerance (well, he was bulilding guidance systems for ballistic missiles ..).

Anyway, if Stihl spilts up A, B, C in < 0.0005", fine maybe I didn't try hard enough to get the most accurate gauges. What I have seen here is NO MENTION of correct piston/cyl tolerances at all, a "Golf is a POS", buy OEM, ect........Yes I did search sorry if I missed it all........

For the purposes of chainsaws I think +/-0.0005" is fine for a good start to a comparison, if not please measure to the best of YOUR ability some NOS assys and post them here. I will be the first to thank you, I don't have +$10,000 to spend on new tools. Last I looked good mics +/-0.0005' were ca. + $200 each, for +/-0.0001" I assume half an order of magnitude more?

P.S.The piston assys (complete) were measured for mass on analytical balances accurate to +/-0.0001 g (masses were rounded to 0.01g), so yes the Mag assys are (that much) much heavier.

P.P.S. I did the best with what was READILY available to me, I hope it helps somebody.........not trying to pi$$ anybody off.....best regards MP

 

[Lakeside53]

10th's are tough... Splitting 10ths is a bi?ch... Nobody is pi$$ed off! ... measurements... well.. when you really have to measure/make something acurately, you find out how hard and expensive it really is!


A friend of mine just retired after running a machine shop for 40 years. He tells me "I'll keep making stuff, , but if I can't measure it with stanley tape, someone else can do it".

 

[Mad Professor]

10th's are tough... Splitting 10ths is a bi?ch... Nobody is pi$$ed off! ... measurments... well.. when you really have to measure/make something acurately, you find out how hard and expensive it really is!


A friend of mine just retired after runniing a machine shop for 40 years. He tells me "I'll keep making stuff, , but if I can't measure it with stanley tape, someone else can do it".

Thanks Andy!. I thought you believed I was feeding you BS.... The mentors I learned from were my uncles, both became master machinists in "ordinance" that kept Russia at Bay in the cold war. One pre-haps made the best (most accurate things to deliver after that war.......) ..........


So how much is A , B, C, pistion/cyls clearance??? Gottcaya?

Best regards,

MP