Bore measuring?

Hi,

first of all, please excuse my english, as i'm french speaking.

i'm in the process of tearing down my engine (Merc 60hp 1993 3 cyl.) with bad compression (was 90-112-115 two years ago and now 90-92-114) to check if i can't simply deglaze and put new rings or if it's too much worn out and i need to rebore it.

It's my first attempt at this and i recently bought a relatively cheap dial bore gauge (http://cgi.ebay.ca/ws/eBayISAPI.dll?ViewItem&ssPageName=STRK:MEWNX:IT&item=370146379884) for measuring the cylinders bore, wich are supposed to be 2.955" stock.

I want to know if i'm using the right procedure cause something seems wrong..I insert the dial indicator in the bore gauge, set it to zero, add a 2.8" anvil, then a 0.1", a 0.05" and a 0.02" spacers, wich lead to a total of 2.970" and insert the gauge in the bore, rocking it slightly to obtain the highest reading, wich came to around 0.0435 (or is it 0.087", i'm not even sure how to read it).

When i substract this from the initial lenght (2.970), it gave 2.9255, wich is smaller than the stock bore!

Is it possible that the initial fixed lenght was off a bit and that i should only use it as a rough estimate? It think of getting a good outside micrometer to put it exactly at 2.970 then zeroing there. Is this the way yo go or is there a simpliest method?

Thanks for helping a novice!

Re: Bore measuring?

Looks like you can set it up at 3", zero and put in and subtract from 3" to get your reading.

Re: Bore measuring?

That the cheap china made guage sold on eBay. It is only good for measureing out of round. Set it up with the closest correct pin and 1 or 2 of the 3 spacer provided. Slide into bore and zero guage.Slide guage SLOWLY down the wall to bottom of cylinder, rotate 180 to clear ports and raise back back up. Note the readings, this will show you where cylinder is worn. To measure correctly you need a periscope type guage, it contacts cylinder in 4 places and is very accurate.This is what I have.

Re: Bore measuring?

Thanks guys!

On this dial (above pic), could you please tell me how much did each increment worth (a full 360 deg is 100 increments)? 0.001" or 0.0005"?

And what method shouls i use to know if they're out of specs?

Re: Bore measuring?

It measures in 1/2 thousands so 5 =.0005 and 10 =.001 and 25 =.0025 and so on. If cylinders are more than .003 oversize its time to rebore.