Correct way to measure a cylinder for wear.

[MercNub]

I bought a couple of old mercury inline 2 cycle 50 hp power heads off ebay so that I would have a backup when my outboard goes south. I have dissembled them and now want to see if the cylinders are in spec. I purchased two tools to accomplish this. One is a T gauge which you drop in the cylinder tighten then measure with a micrometer, and the other is a dial bore gauge which reads .0005 per tick as you run it down the cylinder once you set it to zero for the 2.565 " or 65.15 mm which is the correct standard size for the bore. The Merc. manual says .003 to .004 is the maximum size over the cylinder can be before you have to get it bored out.

My question is how do you accurately measure the cylinder bore with either of the two measuring tools I have.

Thank you in advance.

 

[Faztbullet]

Re: Correct way to measure a cylinder for wear.

Here is diagram on how to measure and check the bores. The dial bore guage will show you where its worn and the t-guage will tell you how much. When I measure a block I use dial bore guage and if its worn(.003 over) I dont even bother to measure I.D it as its getting bored. Your engine should be 2.565(std) to 2.568(max wear)

 

[Moody Blue]

Re: Correct way to measure a cylinder for wear.

What is the difference between the two tools ? Do both not achieve the same results?

 

[Faztbullet]

Re: Correct way to measure a cylinder for wear.

Yes they achieve the same result but to to properly set up a dial bore tool takes to long in my opinion and you still have to use a "mike" either way. I set mine up to a base measurement and zero, then I can see if if measurement are over/under(.003) from base setting. If the taper/wear is under measurement then I measure with t-bar style guages and read the results on a micrometer. A cylinder can be worn evenly and be out of spec's. Below is how to set up a bore guage.

Determine the rough opening with a machinist's rule or micrometer and record the measurement.

2
Select and install the appropriate anvil. The anvil should be long enough to contact the side of the bore and slightly compress the stud when inserted into the hole. Do not use an oversized anvil and try to force the indicator, as this will likely destroy the accuracy of the tool.

3
Select a micrometer in the appropriate range. Most cylinder bores will be in the two-to-three-inch or three-to-four-inch range. Set the micrometer for the target measurement or for an arbitrary measurement. The arbitrary measurement should be close to the target measurement and be an even number that will be easy to do quick math on to arrive at the actual measurement. Record this number on paper with room to do simple addition problems.

4
Insert the anvil and stud between the micrometers machined surfaces. Rotate the bezel until the "zero" is in line with the needle position. The DB indicator is now ready to read a measurement relative to the setting.

Using the Dial Indicator
1
Insert the base of the indicator into the hole. Ensure that the two contact points are 180 degrees from each other and that neither the anvil nor the stud are hanging on scoring or the cross-hatch pattern of the bore wall.

2
Hold the indicator as near to vertical as possible and gently and slightly rock the DB indicator along the anvil/stud axis. The needle will swing clockwise as the tool comes to vertical and the anvil/stud come to their proper position. Read the number on the dial at the point where the needle stops rotating clockwise and attempts to start backing down in a counter-clockwise direction. This is the "relative" measurement. The number may be a positive or a negative . Record this number and remove the DB indicator from the hole.

3
Add or subtract the positive or negative number, respectively, from your target or arbitrary number. This final adjusted number is the actual measurement of the hole.



Read more: How to Use a Dial Bore Gauge | eHow.com http://www.ehow.com/how_5531369_use-dial-bore-gauge.html#ixzz16X59sDC7

 

[MercNub]

Re: Correct way to measure a cylinder for wear.

Thank you for giving me such a great answer. I am going to go through the steps you gave me and remeasure everything again and keep a page in a note book on each power head.

The picture you attached says it all. One the two power heads I took apart the maximum wear is around the ports on either side and right at the top by the spark plug. Also seems the old mercury 45 / 50's from the eighties had a problem with cylinder 4 and cylinder 3. On the 45 hp I bought in 1988 on my bass tracker, cylinder 4 is only 100 psi when I compression test it. Cylinder 3 is 130 and 1 and 2 are both 135. On the 45 hp I just bought off a guy in Ohio, 1 and 2 are 145, 3 is 140 and 4 is 130. Also both the power heads I bought show the most wear in cylinder 4. I wonder why the lower two cylinders show much more wear than the upper two?

Thank you again for the help, it is much appreciated.

 

[Moody Blue]

Re: Correct way to measure a cylinder for wear.

Thanks for the clarification Faztbullet. I have a 4 cyl 800 powerhead sitting in the shop that I plan on rebuilding to replace the existing one on the motor. I went ahead and bought a set of the "T" gauges some time ago but have not yet made the time to really get into the project yet.

If I understand you, you just use the "T" gauges (easier to use) to determine if the bore is oversized and if so, you have the cylinder bored. Whether or not it is tapered or out of round is irrelevant ?

 

[MercNub]

Re: Correct way to measure a cylinder for wear.

After following your directions and with some time I think I got the handle on how to do this. I also have an old caliper type micrometer which I measured the correct stock cylinder size and then set up the t gauge and set the dial bore gauge to zero. I double checked the measurements with two different electronic micrometers and then began measuring the cylinders. The dial bore gauge really shows were the problems are quickly once it is set up. The T gauges are more of a tightness fealing then a little loose where the cylinders are wore. I am going to try to hone the bad cylinder lightly to see if the wore area shows up like you guys said.

Good news is now I will only need to get the bottom cylinder bored it has two areas right around the ports which where .006 over stock, the others just need to get honed. Thanks for your help with this.

 

[basstracker1970]

Re: Correct way to measure a cylinder for wear.

Where can you buy a T gauge at? Been looking cant find them....

 

[Moody Blue]

Re: Correct way to measure a cylinder for wear.

Search for "telescopic bore gauge" on places like ebay.

http://shop.ebay.com/i.html?_nkw=te...e+gauge&_osacat=0&_trksid=p3286.c0.m270.l1313

 

[Faztbullet]

Re: Correct way to measure a cylinder for wear.

You can get them at Harbor freight and you will need the items below to do it correctly.(the stand makes it easy as it frees up hands) The "mike" set will do just about anything you will need to measure on a "inline" from engine to gearcase...

http://www.harborfreight.com/hand-t...ators-micrometers/micrometer-stand-95918.html

http://www.harborfreight.com/hand-t...micrometers/3-piece-micrometer-set-66512.html