bclapham

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Nov 5, 2001
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i am rapidly learning in life that most tasks run smoothly when i make measurements before the task, no more so in engine rebuilding.

I am looking to measure 2 things...

1. TDC, is there a dial type guage available that will screw into the spark plug hole, so i can set TDC for timing purposes without taking the head off?

2. Bore measurements. I found this old thread here http://dirtrider.net/forums3/showthread.php?threadid=65220&perpage=20&display=&pagenumber=2

Rich described a "Fowler Bore Guage" and if anyone knows an online source please let me know, sounds like tehy are around $100.

During my research, i also found a "telescopic guage set" like this

http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=5649

I am by no means a cheap ass, but i wonder if i can use such a guage to measure the cylinder bore with the help of my digital calipers? I know it sounds daft, but this could be a better way of measuring piston clearance since we are comparing 2 measuremetns from the same tool rather than relying on the measurements from 2 different tools being accurate However, i do apprieciate, that the precision of this method could be somewhat unreliable!

thanks

Bruce
 

Rich Rohrich

Moderator / BioHazard
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Jul 27, 1999
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Bruce - The Fowler bore guage is available online from www.jlindustrial.com for less than $100 and you can also get a decent micrometer from them as well.

Telescoping "pop" guages are great tools but totally unsuitable for the task at hand. For under $200 you can't get bore measuring tools that will (with appropriate care) last a lifetime.
 

bclapham

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Nov 5, 2001
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Rich:

when it comes to measuring pistons, is a digital caliper not the best tool for the job (but is better than nothing!) and a good quality micrometer is required, correct?

and the beauty of the bore gauge, is that you can measure front to back and side to side within the bore to get an estimation of roundness in addiition to bore diameter, correct?

(i am assuming that the front to back wear is occurs generally more than side to side?)

its funny since my main motivation for using the didgital gauge is it is in metric....i have a funny feeling many of the measuring tools will all be in inches, a concept that still gives me bother!

just out of interest, i found this interesting little goodie on my internet travels this lunch! i recon i might try and fettle one of these up!

http://www.jaysmithracing.com/images/TDC Tool/TDC 1.JPG

thanks

ps whilst i have your attention, thank you for my avatar nomination!:)
 

Jaybird

Apprentice Goon
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With calipers you are fairly restricted on what part of the jug you can measure, yes? Bore guage you can get a full diagram of the total cylinder.
 

jmics19067

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Jan 22, 2002
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A question about how to measure please. As a casual play rider<also for other mundane personal vehicles and production type work> I use the telescopic bore gauges and had no apparent ills. I would make a machinist cringe though since I really don't measure anything. I take my standard bore measurement and then add in the wear limit to it. I then set my micrometer to that measurement and then "pop" the telescopic gauge inside the micrometer. My purpose is in only making a "no go " gauge.
As I said I have no real measurements of the bore but if my gauge does not pass thru the bore in any spot I gather that the bore is still usable. I have been doing it this way ever since trying to use the pop gauge in a 2 stroke cylinder and having a futile attempt at measuring near ports. This method allows me to "measure" close to the ports without having to try and wiggle the gauge falling into a port.

My question is that although my method has no true accurate measurements and cannot tell you how worn the bore is, is this method good enough to just answer the question "put a piston in it or send it out for boring"? Any thoughts on if am screwing it up and why would be greatly appreciated.
 

Jaybird

Apprentice Goon
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jmics,
You would probably be more accurate by seeing if a new ring in the cylinder had an overage of end-gap.
 

jmics19067

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Jan 22, 2002
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oh wow I like that idea

would I subtract not worn out bore ring end gap from worn out area bore ring gap and divide by pi to get my wear limit? or would it be

<worn out area ring end gap divided by pi> minus< standard bore ring end gap divided by pi>

thanks
 

Jaybird

Apprentice Goon
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I only suggested the ring trick as an alternative. It could let you know real fast if the cylinder was out of spec. with a large gap and most folks have, or can easily obtain, feeler guages.

Knowing what the circumference of the new cylinder would be and what the ring-end gap should be in such, yes you could take the circumference of a past spec cylinder...subtract the measurement of the new and you would know how much distance your ring ends should have best and worse case.

Without a bore guage, it will be hard to map the egging of a jug.
 

jmics19067

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Jan 22, 2002
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well having a decently reputable guestimate is what I was looking for and I always had trouble right around the transfer ports. I am assuming that if you measured your end gap of the ring and the very top of the cylinder<not worn> then slid the ring down to where the piston actually rides. If there is no end gap change or gap between the cylinder wall and ring I should be extremely close to a servicable jug.

An easy way to spot trouble and if I see something I dont like then I can break out the telescopic gauges and try to narrow it down.
 
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