piston protrusion 'how to' w/ pics!

I looked for a while and didn't find a good how to for this on the tdiclub site. I ended up having to google it; it's scary in other forums so I thought I would make it so others never have to leave!

First, the parts... you only need two tools. the first is the dial indicator itself, the second is a bridge to hold it while you measure.
Depending on why you are checking the protrusion accuracy is not as important as consistency. If all you are doing is checking for a bent rod, you just need to know if on piston is "off" from the others. If you are doing anything else you probably already know what you need.
I got this digital indicator form harbor freight. It reads in inches and mm and you cane tare it to zero which is handy.
https://www.google.com/webhp?source...sb&fp=c4aec0292ce16d20&biw=1280&bih=702&ion=1
If you buy snap on products and just like to spend lots of money on tools (kidding) you can get nicer ones here: http://www.mcmaster.com/#dial-indicators/=ghngtd

The next thing you need is a bridge, I got mine from summit racing since they are close and ship same day. It's the program three hole stand in the search results. Jeggs also has some if you want to get it form them. They are all the same really, my only recommendation is getting one that has multiple holes as they come in handy (get your mind out of the gutter). If you want to step it up some come with magnetic bases that will help you get a more accurate reading.
https://www.google.com/webhp?source...sb&fp=c4aec0292ce16d20&ion=1&biw=1280&bih=702

Now you are ready to get started! first you need a clean block (deck) surface. if you search the forums I have a thread on how to clean it (it's here http://forums.tdiclub.com/showthread.php?t=344585). It should look like this:


To measure the protrusion first bring two of the cylinders even with the block deck. Place the dial indicator into the bridge and set it to measure the height of the block surface. tare the indicator to zero, and shift it over to measure the piston in one of the four corners. Now get your buddy to slowly turn the crank until the dial indicator goes up to a max level and then start to come back down. Now tell your buddy to turn it the other way. then the other way. then the other way. etc. until you have a maximum height reading for that corner. now shift to another corner on the same piston, rinse and repeat. After you have four readings for each cylinder take the average reading for each.
tare to zero on the block deck:

Find the highest point in the travel:

If applicable make sure your "buddy" is your dad. You both will thank me later. He will also have better handwriting. Note: You are never to old to ask your dad to help you work on your car.

Continue to measure until satisfied. You will never get the same reading twice, thats just science. You could measure two hundred times to get a better data set but it will never be perfect (engineers will understand).


After you are done you should have a bunch of tiny numbers (remember that 0.94756234 millimeters!). If they are all roughly the same you have no bent rods! if you one jumps out at you as "off" now is the time to start drinking, heavily, because its going to be a pain in the ass to fix it and you have likely gotten yourself into something over your head !

Great post! Sticky?

Redneck Truck said:

Great post! Sticky?

Click to expand...

Sure seems like a good candidate to me.

Is there a good way to permalink to other threads? I would like to link my surface preparation thread to it as well:

http://forums.tdiclub.com/showthread.php?t=344585

Also, someone help me out and post the tolerance specs for maximum difference between lowest and highest reading, maximum protrusion, and minimum protrusion (if they exist). The measurements for the available head gaskets I found here:

From the data I have seen the following gaskets for piston protrusion:

1 hole: 0.91-1.00 mm
2 hole: 1.01-1.10 mm
3 hole: 1.11-1.20 mm

Gasket thickness for the gaskets available:
1 hole: 1.55 mm
2 hole: 1.63 mm
3 hole: 1.71 mm
http://forums.tdiclub.com/showthread.php?t=330816&page=2

Some other fun facts that are related:
"Keep in mind that the rods are designed to withstand 3000psi" So you wont likely bend a rod just from valve interference.
http://forums.tdiclub.com/showthread.php?p=2884864&highlight=protrusion+tolerances#post2884864

We need a wiki and a chat room...

Myturbodiesle.com

And we have an IRC chat room.

IRC? from the time of mIRC? From the early 90's? Wow, those were good times growing up looking for games to download on these chat rooms.

Digital Corpus said:

Myturbodiesle.com

And we have an IRC chat room.

Click to expand...

Turns out there is a TDICLUB IRC channel as well. The myturbodiesel site is a good resource too though!

Enabled said:

IRC? from the time of mIRC? From the early 90's? Wow, those were good times growing up looking for games to download on these chat rooms.

Click to expand...

I actually think it's amazing that IRC is still relevant...

dislexicmofo said:

I looked for a while and didn't find a good how to for this on the tdiclub site. I ended up having to google it; it's scary in other forums so I thought I would make it so others never have to leave!

First, the parts... you only need two tools. the first is the dial indicator itself, the second is a bridge to hold it while you measure.
Depending on why you are checking the protrusion accuracy is not as important as consistency. If all you are doing is checking for a bent rod, you just need to know if on piston is "off" from the others. If you are doing anything else you probably already know what you need.
I got this digital indicator form harbor freight. It reads in inches and mm and you cane tare it to zero which is handy.
https://www.google.com/webhp?source...sb&fp=c4aec0292ce16d20&biw=1280&bih=702&ion=1
If you buy snap on products and just like to spend lots of money on tools (kidding) you can get nicer ones here: http://www.mcmaster.com/#dial-indicators/=ghngtd

The next thing you need is a bridge, I got mine from summit racing since they are close and ship same day. It's the program three hole stand in the search results. Jeggs also has some if you want to get it form them. They are all the same really, my only recommendation is getting one that has multiple holes as they come in handy (get your mind out of the gutter). If you want to step it up some come with magnetic bases that will help you get a more accurate reading.
https://www.google.com/webhp?source...sb&fp=c4aec0292ce16d20&ion=1&biw=1280&bih=702

Now you are ready to get started! first you need a clean block (deck) surface. if you search the forums I have a thread on how to clean it (it's here http://forums.tdiclub.com/showthread.php?t=344585). It should look like this:


To measure the protrusion first bring two of the cylinders even with the block deck. Place the dial indicator into the bridge and set it to measure the height of the block surface. tare the indicator to zero, and shift it over to measure the piston in one of the four corners. Now get your buddy to slowly turn the crank until the dial indicator goes up to a max level and then start to come back down. Now tell your buddy to turn it the other way. then the other way. then the other way. etc. until you have a maximum height reading for that corner. now shift to another corner on the same piston, rinse and repeat. After you have four readings for each cylinder take the average reading for each.
tare to zero on the block deck:

Find the highest point in the travel:

If applicable make sure your "buddy" is your dad. You both will thank me later. He will also have better handwriting. Note: You are never to old to ask your dad to help you work on your car.

Continue to measure until satisfied. You will never get the same reading twice, thats just science. You could measure two hundred times to get a better data set but it will never be perfect (engineers will understand).


After you are done you should have a bunch of tiny numbers (remember that 0.94756234 millimeters!). If they are all roughly the same you have no bent rods! if you one jumps out at you as "off" now is the time to start drinking, heavily, because its going to be a pain in the ass to fix it and you have likely gotten yourself into something over your head !

Click to expand...

This is all great, love the humor. Have an engine to swap and now they’re being pricks about covering cost of a worn cam, so I may check rods and replace head. Thx!

I keep finding people using this method to check piston protrusion. I just found this recently. I know it's been here a long time, but honestly, the method is incorrect. Sorry if I am stepping on any toes, but I have spent the time and effort to get this right.

Measurements near or at the skirt side of the piston are an inaccurate method to measure projection because the piston will rock in the bore on the wrist pin. That means if you measure on the skirt side of the piston, the measurement can be high or low. You can set up the dial indicator at the center of the skirt side and by pushing the piston front to back, measure the deflection.

The only point that will give consistent and accurate reads is directly above the wrist pin, or as describe it, 'like sitting in the middle of the rowboat.' It may rock side-to-side, but the center is stabile.

Draw a line through the center of all 4 pistons in a row. Where the line intersects the piston, zero the stylus on the block, then with the piston just below deck height, move the stylus over the edge of the piston crown, on the thin shoulder outside the valve relief. Make sure there is no buildup of carbon on the piston where you are measuring. Note: Some later model pistons have the shoulder cut out from the valve relief to the edge of the piston. The depth of the valve relief is usually .039" or 1mm. So, the valve relief should come up flush, or slightly tall (.004") to the block if you are using a 2-hole head gasket.

Turn the crank sprocket bolt with a 19mm 12pt socket, two ft long 1/2" drive extensions and a breaker bar, turn the engine to make the piston roll through TDC, noting the highest read. Do the same on the opposite side of the same piston. Record the readings. Repeat on the rest of the pistons.

If any piston or any side of a piston is more than .005" variance, you have either a bent rod or a crushed piston. Pay particular attention to any cylinder that either valves were bent or lifters were smashed, as that is the most likely location for piston/ rod damage.

Be aware, that a deviation of .004" equals .5 point loss in compression ratio, so accuracy counts.

And now, The Rest of the Story...

There is another deviation in the head that can cause either the wrong head gasket selection, but worse, the head gasket will not seal and when your purpose was to fix a blown head gasket, your rebuild blew the head gasket again...

This is a problem with the TDI's that are regularly run hard. The block will warp into a valley, with the webs between cylinders as the low spot. It is difficult to witness, as the typical method would be to use a flat edge and a .001" feeler gauge. The problem is the feeler gauge will fool you when it pinches on the embossing on the block caused by the head gasket impression. Unless you use a machinist's bar and bright light behind the bar, you will not see the warp. Our other method is to strike a bastard file across the block by palming the file. If the cut is only at the length of the block on either side, that means the center of the block is low and needs to be corrected.

The point is, although the measurements down the center of the head will be accurate, the head bolts have distorted the block, pulling the outer edge of the block, and the length of the block, up. We have seen this deviation as much as .004". So, that is another reason measuring at the skirt side will be inaccurate.

Before any measurements for piston height can be properly made, the block should be made flat. However, when the resurfacing of the block is done carefully, the height at the webs between the cylinders will not change. The same head gasket can be used. So, if you don't think this engine isn't strange enough already, when I resurface a block, I can remove .004" of material on the sides and not change head gasket thicknesses.

I can't figure out how to upload an image. I apologize. For anyone. Still interested. Here is the chart for head gasket thickness according to Bentley manual.

I ran across this thread while measuring my piston protrusion during a conversion of my 1.9 TDI into a 2.0 TDI. Using the BEW block

I have a YouTube playlist documenting the whole procedure if anyone would like to follow along.