Hi all,

I've been thinking of rebuilding my old D15 motor. I am wondering if I can use my Mitotoyo digital caliper and bore gage (see attached pictures) to measure the bore size. Will it be accurate enough? I don't want to invest a few hundread dollars just to rebuild one old D15 motor...

 

That caliper is accurate enough but from experience, it's easier to upsize the piston and have the machine shop overbore the cylinders. This way you don't have to worry about measuring anything other than bearing clearances and you'll have guaranteed fitment with consistent piston to wall clearance not to mention the block is almost truly starting over at 0 miles.

I recently bought similar bore gauges but have yet to use them on an actual rebuild. I tested them out on an old bare block and really the accuracy is all dependent on how well you can consistently position and hold them.

 

You are probably right. It's easier just to buy oversize pistons and throw the block to machine shop and let them worry about the rest...

But right now I want to see if the current block and pistons are still in usable limit. It is my spare motor. I want to get fun out of rebuilding it. It is kind of luxurious to throw money into a motor i will be stored away for i don;t know how long....

I think I will take it apart first to see how bad it is inside. If it looks rough and it for sure need to be bored out, then i will just take it to machine shop. If not, I may have to buy a set of bore gage from harbor freight (about $15) and measure the bore sizes with my caliper......

Theoretically, the caliper is accurate enough... But I don't know how consistent the reading will be in reality. If I will have to invest into a micrometer, I may have to think about it./... Maybe a set of oversized pistons is a better choice?

 

i used a set bore gauges and a digital caliper for my b16a rebuild. as long as you keep your method constant then you should get accurate results. i took measurements of each cylinder at 3 different heights, with 4 measurements each 90 degrees apart at each height (ie measure at 12o'clock, 3o'clock, 6o'clock and 9o'clock). i then repeated this whole process 3 times so i could average out the readings. if you end up with different readings for each measurement iteration then either your technique is bad or the tools aren't very accurate. i got pretty consistent measurements with this method so i'm pretty confident it will be fine

 

Those calipers are accurate, but the method of measurement will be near impossible to keep consistent. You'll get a drastically different measurement depending on how hard/light you're pressing on them.

At work it's common knowledge that although calipers can read to 2+ decimal places, they're really only reliable to 1 decimal place which isn't accurate enough for boring a motor.

There's a chance you'll get it to work, but you couldn't rely on it.