piston to wall clearance
Melting Slicks
Joined: Jan 2004
Posts: 2,672
Likes: 1
From: New Cumberland PA
Originally Posted by Twin_Turbo
What?? You measure the piston skirt diameter w/ a set of vernier calipers first and then the bore w/ a bore gauge, the difference is your clearance.
Race Director
Joined: Dec 1999
Posts: 16,945
Likes: 9
Well...without going into the detail o the correct denomination of the procedure...that's how it's done correctly. And if you want to discuss errors, there's 2 measurements errors, one for the bore measurements and 1 for the piston measurements, the calculation does not introduce another meaningful propagating fault into the total (because the error is smaller by 1 significant number than the measuring errors, the rounding off/reading is already done there) so you measure 2 dimensions...calculating is just part of the process....
Race Director
Joined: Nov 2000
Posts: 11,872
Likes: 12
From: Waterloo ontario Canada
Originally Posted by mandm1200
If you do it that way, you did not measure the piston to wall clearance, you calculated it. There is a big differnce between measuring and calculatiing it.
I have a proper bore gage and you just mike the piston and regardless of what it reads set the bore gage to this value, it is just a dial gage that you zero using the mike on the piston to find zero, Anyway you zero the gage and then put it in the bore and the difference between the zero you set on the gage and the new reading on the gage is the piston to wall clearance.
Feel gages are for setting valves and NOT for piston to cylinder wall or bearing clearance.
Drifting
Joined: May 2004
Posts: 1,442
Likes: 2
From: Flanders NJ
Originally Posted by Twin_Turbo
What?? You measure the piston skirt diameter w/ a set of vernier calipers first and then the bore w/ a bore gauge, the difference is your clearance.
I wouldn't use a feeler gauge, the feeler is a flat strip of metal, if you use it to measure bore to skirt clearance the strip actually has to bend and even though it will bend it may not be willingly enough to bend to allow the feeler(s) with the exact clearance thickness to be inserted meaning you can just slide in one that's a tad smaller, this will lead you to believe you have a tight clearance when in all reality it may be slightly larger...and it's not inches we're talking about here. If you are serious in building your engine be prepared to spend some money to buy a bore gauge, you don't use a hammer to remove and install a damper also so why not use the proper tools to measure critical dimensions.
I wouldn't use a feeler gauge, the feeler is a flat strip of metal, if you use it to measure bore to skirt clearance the strip actually has to bend and even though it will bend it may not be willingly enough to bend to allow the feeler(s) with the exact clearance thickness to be inserted meaning you can just slide in one that's a tad smaller, this will lead you to believe you have a tight clearance when in all reality it may be slightly larger...and it's not inches we're talking about here. If you are serious in building your engine be prepared to spend some money to buy a bore gauge, you don't use a hammer to remove and install a damper also so why not use the proper tools to measure critical dimensions.
You can't measure between two curved surfaces with a flat feeler gage. Also, if you measure that way from one side the piston can move because of the clearance on the opp. side. It does not take any special skills to read a mic or a vernier, especially the digital ones.
Race Director
Joined: Oct 2000
Posts: 15,013
Likes: 79
From: central FL, near the beach.
Great Topic
there are at least 3 types of feeler gauges, only 1 is for valves.
Norval
please tell how you check ring side clearance.
(others feel free to chime in)
.
i build my motors without any binding that could ruin them. the lowly feeler gauge has prevented disaster several times. once i found a tight spot on a piston, that on close inspection appeared to have been dropped. a mic would have missed that!
i'm glad my auto shop teacher,in 1970, showed the class all the things to measure with a feeler gauge. i've never had a blown up engine in 35 yrs.
Norval
please tell how you check ring side clearance.
(others feel free to chime in)
.
i build my motors without any binding that could ruin them. the lowly feeler gauge has prevented disaster several times. once i found a tight spot on a piston, that on close inspection appeared to have been dropped. a mic would have missed that!
i'm glad my auto shop teacher,in 1970, showed the class all the things to measure with a feeler gauge. i've never had a blown up engine in 35 yrs.
Last edited by Matt Gruber; Feb 10, 2005 at 09:23 AM.
Pro
Joined: Jan 2003
Posts: 642
Likes: 0
From: Baton Rouge LA
We build a lot of motors here and we stand behind them and warranty them. There is no a way a motor would leave this shop with anything other then valve lash measured with a feeler gauge. Our blue print sheets are accurate down to the hundred thousandths and include every measurement of the engine from rod bolt stretch (not torque) to the Ra of the cylinder walls, block, and head surfaces. There is one correct way to do it and another way that will work too.
.
.
Melting Slicks
Joined: Jan 2004
Posts: 2,672
Likes: 1
From: New Cumberland PA
I don't think anyone who used a feeler gauge would say with absolute certainty that is is wrong to calculate the clearance with calipers and bore gauge. Personnaly, I think that is a proper way to do it. Not only has someone said that a feeler gauge is not the best way to do it, that it was wrong.
I also believe the the feeler gauge is also proper. Feeler gauges come in different widths as well as thickness. The thin blades do bend to fit between piston and wall. There is a margin of error no matter how it is done. As long as measurement with error is within the tolerances set by the manufacture of the product, then these two methods should be acceptable.
I also believe the the feeler gauge is also proper. Feeler gauges come in different widths as well as thickness. The thin blades do bend to fit between piston and wall. There is a margin of error no matter how it is done. As long as measurement with error is within the tolerances set by the manufacture of the product, then these two methods should be acceptable.
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Race Director
Joined: Nov 2000
Posts: 11,872
Likes: 12
From: Waterloo ontario Canada
Originally Posted by Matt Gruber
there are at least 3 types of feeler gauges, only 1 is for valves.
Norval
please tell how you check ring side clearance.
(others feel free to chime in)
.
i build my motors without any binding that could ruin them. the lowly feeler gauge has prevented disaster several times. once i found a tight spot on a piston, that on close inspection appeared to have been dropped. a mic would have missed that!
i'm glad my auto shop teacher,in 1970, showed the class all the things to measure with a feeler gauge. i've never had a blown up engine in 35 yrs.
Norval
please tell how you check ring side clearance.
(others feel free to chime in)
.
i build my motors without any binding that could ruin them. the lowly feeler gauge has prevented disaster several times. once i found a tight spot on a piston, that on close inspection appeared to have been dropped. a mic would have missed that!
i'm glad my auto shop teacher,in 1970, showed the class all the things to measure with a feeler gauge. i've never had a blown up engine in 35 yrs.
If I want .0045 clearance that is what I want and not something greater then a .005 feel gage.
Machine shops all know me and know I take my own mikes to check their work. I never agrue about the price, mostly tip a little extra but I demand exact work and I get it.
The forman usually take care of me personally. He know I know good workmanship and will be checking.
Tech Contributor
Joined: Aug 1999
Posts: 14,374
Likes: 6,373
From: At my Bar drinking and wrenching in Lafayette Colorado
Norval -
Good to see someone knows correct way to check tolerances. Like you, I have my own dial bore gauges and a set of mic's. I check every bore and every piston on every engine I put together. There's only one right way to measure the clearance of a piston in a bore - I can't believe there's even a discussion about it here. I've been involved in aerospace machining and measuring operations for 30 years. To check fit of a piston in a bore, you mic the piston and measure the bore with a bore gauge. Period. The piston is measured at the skirt (below the ring land and above the bottom edge) with a micrometer - not with dial calipers (and not with a feeler gauge).
Race Director
Joined: Oct 2000
Posts: 15,013
Likes: 79
From: central FL, near the beach.
Norval
do you ever check ring side clearance?
my old pistons were .004", WAY over the .002" stock. that motor got new pistons.
.(not talking end gap).
.
i am not suggesting a machine shop use only feeler gauges(they don't have the time)!
On mock up assembly feeler gauges tell the true story
WILL IT SPIN FREE OR BIND (when hot)
feelers are a final GO/NO GO test.
my feelers can only read in 1/2 thou. .001. .0015, .002 .0025 .003 .0035
That is close enough to CHECK THE WORK of a shop.
do you ever check ring side clearance?
my old pistons were .004", WAY over the .002" stock. that motor got new pistons.
.(not talking end gap).
.
i am not suggesting a machine shop use only feeler gauges(they don't have the time)!
On mock up assembly feeler gauges tell the true story
WILL IT SPIN FREE OR BIND (when hot)
feelers are a final GO/NO GO test.
my feelers can only read in 1/2 thou. .001. .0015, .002 .0025 .003 .0035
That is close enough to CHECK THE WORK of a shop.
Race Director
Joined: Nov 2000
Posts: 11,872
Likes: 12
From: Waterloo ontario Canada
Originally Posted by Matt Gruber
Norval
do you ever check ring side clearance?
my old pistons were .004", WAY over the .002" stock. that motor got new pistons.
.(not talking end gap).
.
i am not suggesting a machine shop use only feeler gauges(they don't have the time)!
On mock up assembly feeler gauges tell the true story
WILL IT SPIN FREE OR BIND (when hot)
feelers are a final GO/NO GO test.
my feelers can only read in 1/2 thou. .001. .0015, .002 .0025 .003 .0035
That is close enough to CHECK THE WORK of a shop.
do you ever check ring side clearance?
my old pistons were .004", WAY over the .002" stock. that motor got new pistons.
.(not talking end gap).
.
i am not suggesting a machine shop use only feeler gauges(they don't have the time)!
On mock up assembly feeler gauges tell the true story
WILL IT SPIN FREE OR BIND (when hot)
feelers are a final GO/NO GO test.
my feelers can only read in 1/2 thou. .001. .0015, .002 .0025 .003 .0035
That is close enough to CHECK THE WORK of a shop.
With the mics are also proof rods, I check the mike against them often and even the temperature of the mic and pistons must be the same.
Not everyone can measure properly with a mic. a vernier is definitely out for measureing. It takes alot of practice to really use a mic properly but with a bore gage you don't actually care about the reading only the diffence which the dial indicator on the bore gage reads. The mic is only used to zero the bore gage.
And again Matt I was wrong, feeler gages have their place like ring gap, ring side clearnace but not where we are working in 1/2 thousands.
Race Director
Joined: Nov 2000
Posts: 11,872
Likes: 12
From: Waterloo ontario Canada
Originally Posted by Matt Gruber
sure beats talking to the neighbors!
.
coming soon:
heated dscussion on bearing crush!
Sticking a dial indicator on the end of the axle for example and then pushing in and pulling out and reading the difference is wrong and will be about .004 out from the true reading.
Race Director
Joined: Nov 2000
Posts: 16,416
Likes: 1
From: NC,USA
Originally Posted by Matt Gruber
sure beats talking to the neighbors!
.
coming soon:
heated dscussion on bearing crush!
The Vernier Caliper you speak of TT... I've only see this type of digital read out:
I have a dial caliper, but I've always been under the impression that they are only accurate to 1-3 thousanths where as a micrometer is accurate to the 10th of a thousandth?
All of a sudden I'm not as confident to just slap my parts together and call it done!
Race Director
Joined: Nov 2000
Posts: 16,416
Likes: 1
From: NC,USA
Originally Posted by norvalwilhelm
Looking forward to it. My son taught me alot about measuring bearing preload and I will bet 99% of the people here don't know positively how to measure bearing end play.
Sticking a dial indicator on the end of the axle for example and then pushing in and pulling out and reading the difference is wrong and will be about .004 out from the true reading.
Sticking a dial indicator on the end of the axle for example and then pushing in and pulling out and reading the difference is wrong and will be about .004 out from the true reading.
I havent got a clue how you do that...
Le Mans Master
Joined: Mar 2004
Posts: 7,470
Likes: 1,490
From: Little Rock AR
I can't believe this thread either. If someone was asking this question here, they obviously do not have a bore gauge in the tool box in the first place. How did I get re-directed to the NCRS board?
If you want the NASCAR quality job, take it to a qualified shop, pay the spcialist to have the job done "Right". Otherwise find a shade tree, a feeler gauge set and have at it.
There is always a "right" way to do a job but for practical purposes there are other ways of getting "close enough" for us amatures.
-Mark.
If you want the NASCAR quality job, take it to a qualified shop, pay the spcialist to have the job done "Right". Otherwise find a shade tree, a feeler gauge set and have at it.
There is always a "right" way to do a job but for practical purposes there are other ways of getting "close enough" for us amatures.
-Mark.
Instructor
Joined: Jan 2005
Posts: 218
Likes: 0
From: Sheridan IL
You are lost! I would love to leak one of your engines down. 
Originally Posted by Matt Gruber
u don't measure piston to wall clearance with a bore gauge, do u? u must be joking 
The micrometer salesman REALLY sold u guys. Prolly sold u a ring side clearance mic too!
The micrometer salesman REALLY sold u guys. Prolly sold u a ring side clearance mic too!