SpeedTalk Store - Opinion Columns

Piston to pin clearance question

General engine tech -- Drag Racing to Circle Track

Moderator: Team

Piston to pin clearance question

Postby apprentice1 » Wed Apr 20, 2011 9:34 pm

I'm assembling a 540 BBC for a customer: street driven 4X4 and probably a little mudbogging thrown in :) . Running the pins through the pistons I found some to have a more resistance compared to others so I decided to measure the clearance using the sunnen dial comparator on our rod honing machine. I found that all the pistons appear to have the same clearance, whether they feel tight or not, and that this clearance is .0017". According to my research this seems large...is it anything to worry about? I had been thinking of giving the tight piston's a few strokes on the hone...but haven't really seen any recommendations for having the piston to pin clearance greater than .0013". SRP 140329 Pistons, 2618 material, piston weight 625g, 4.5" bore. JE Piston Pins 990-2930-15-51S...nothing special. The entire rotating assembly is one kit from SCAT, so im not mixing and matching parts and pieces. Thanks for your replies.
apprentice1
Member
Member
 
Posts: 165
Joined: Sat Oct 16, 2010 6:21 pm

Re: Piston to pin clearance question

Postby hodge » Wed Apr 20, 2011 9:48 pm

that clearance is loose I find that at .001" the pins fall through, and you shouldn't feel any resistance. clearance over .0015" will need some good thick oil. I've seen them run at .003" no problems but take that clearance in to account,I would confirm your clearance use an inside bore gauge other than the ag 300 .and how did you set it up not to be a smart a-s.
hodge
Expert
Expert
 
Posts: 720
Joined: Mon Jul 27, 2009 8:05 pm
Location: St Catharines Ontario

Re: Piston to pin clearance question

Postby ProPower engines » Wed Apr 20, 2011 11:11 pm

I would suggest using a clearance of .00050-.0007 pin clearance but I think your gauge may need to be reset and checked.
Mic the 2 pins you use to set the Ag300 and then use a small bore gauge if you can to check the pin boss ID.
Or use the pins to set the Ag300 then use a pin as a standard and mic it and compare the mic'd size to the "0" on the Ag300 they should be the same. Checking pin bores may require you to use a different set of gauge point locations depending on the piston design. Which set of threaded holes do you have the points in?
Real Race Cars Don't Have Doors
ProPower engines
Guru
Guru
 
Posts: 5350
Joined: Sun Jan 21, 2007 1:16 pm
Location: VICTORIA BC CANADA

Re: Piston to pin clearance question

Postby CNC BLOCKS » Wed Apr 20, 2011 11:42 pm

apprentice1 wrote:I'm assembling a 540 BBC for a customer: street driven 4X4 and probably a little mudbogging thrown in :) . Running the pins through the pistons I found some to have a more resistance compared to others so I decided to measure the clearance using the sunnen dial comparator on our rod honing machine. I found that all the pistons appear to have the same clearance, whether they feel tight or not, and that this clearance is .0017". According to my research this seems large...is it anything to worry about? I had been thinking of giving the tight piston's a few strokes on the hone...but haven't really seen any recommendations for having the piston to pin clearance greater than .0013". SRP 140329 Pistons, 2618 material, piston weight 625g, 4.5" bore. JE Piston Pins 990-2930-15-51S...nothing special. The entire rotating assembly is one kit from SCAT, so im not mixing and matching parts and pieces. Thanks for your replies.


You shouldn't feel any resistance with .0017 clearance, On pistons with a .990 pin we run .001 to .0013 clearance.

We bore gauge all our pin bores and most pistons need honing to acheive the .001 except the Mahle pistons those seem to fall right at .001 to .0012 and so far have never had to hone a set of those pistons before.

We just had a set of Diamond turbo pistons come in the measured .0012 which is rare. Most Dimaond pistons need honing!!

It hard to measure pin bores with an AG-300 gauge.
Last edited by CNC BLOCKS on Wed Apr 20, 2011 11:44 pm, edited 1 time in total.
Website is up and running
http://hinksonautomotive-cncblocks.com/
Machine shop tour
http://hinksonautomotive-cncblocks.com/shop-tour/
Monthly Specials
http://hinksonautomotive-cncblocks.com/specials/
Soon 55MM babbit cam bearings with 1 hole
CNC BLOCKS
Guru
Guru
 
Posts: 4516
Joined: Thu Jul 01, 2004 5:34 am
Location: NORTHEAST

Re: Piston to pin clearance question

Postby grant6395 » Wed Apr 20, 2011 11:43 pm

i think big joe would have something to say about running .0005-.0007 pin clearance.too tight in my opinion.especially with something that makes crankcase vacuum.(in drag race situations,of course)
grant6395
Pro
Pro
 
Posts: 278
Joined: Mon Oct 18, 2010 3:51 pm

Re: Piston to pin clearance question

Postby needforspeed66gt » Wed Apr 20, 2011 11:46 pm

.0005"-.0007" is fine for that application, I would go ~ .0008" on the rod to pin....assuming it's not dry sumped or running a vac pump.

Another thing to check on your setup is the centralizer pin, you should have a setting ring with a slot in the bottom for setting up the gauge. Are you using the setting fixture that holds 2 pins, or are you just setting with a hand mic?
Nate
Engine Machinist
User avatar
needforspeed66gt
Guru
Guru
 
Posts: 1813
Joined: Sat May 06, 2006 5:18 pm
Location: North Bay, California

Re: Piston to pin clearance question

Postby apprentice1 » Wed Apr 20, 2011 11:57 pm

I have the points in the holes that are the farthest out. I had set the ag300 with a mic set to the wrist pin size...I don't think we have a way to set it over 2 pins, ill check tomorrow. But look at my name...i'm learning...and thanks for bearing with guys like me and answering all our questions. It is much appreciated. I will have to check with a dial bore guage tomorrow. Thanks again for the replys.
apprentice1
Member
Member
 
Posts: 165
Joined: Sat Oct 16, 2010 6:21 pm

Re: Piston to pin clearance question

Postby apprentice1 » Thu Apr 21, 2011 12:00 am

yes I had checked the centralizer pin with the setting ring...but of course if I'm off because a hand mic isn't good enough...
apprentice1
Member
Member
 
Posts: 165
Joined: Sat Oct 16, 2010 6:21 pm

Re: Piston to pin clearance question

Postby ProPower engines » Thu Apr 21, 2011 1:26 am

[quote="needforspeed66gt"].0005"-.0007" is fine for that application, I would go ~ .0008" on the rod to pin....assuming it's not dry sumped or running a vac pump.quote]

Yup that was my thought as well for a street truck. No mention of oil system or vac. pump.

Carl
Are you seeing the heat in street stuff for that much clearance? I would have thought a bit tighter I have a hard time seeing a pin grow that much over the boss.
Real Race Cars Don't Have Doors
ProPower engines
Guru
Guru
 
Posts: 5350
Joined: Sun Jan 21, 2007 1:16 pm
Location: VICTORIA BC CANADA

Re: Piston to pin clearance question

Postby apprentice1 » Thu Apr 21, 2011 1:37 am

it is not dry sump and it will not have a vac pump
apprentice1
Member
Member
 
Posts: 165
Joined: Sat Oct 16, 2010 6:21 pm

Re: Piston to pin clearance question

Postby needforspeed66gt » Thu Apr 21, 2011 2:23 am

Image


The setting fixture is explained in this set of instructions.

http://www.sunnen.com/graphics/assets/d ... be80c6.pdf
Nate
Engine Machinist
User avatar
needforspeed66gt
Guru
Guru
 
Posts: 1813
Joined: Sat May 06, 2006 5:18 pm
Location: North Bay, California

Re: Piston to pin clearance question

Postby CNC BLOCKS » Thu Apr 21, 2011 6:11 am

ProPower engines wrote:
needforspeed66gt wrote:Carl
Are you seeing the heat in street stuff for that much clearance? I would have thought a bit tighter I have a hard time seeing a pin grow that much over the boss.


Most sreet engines are press fit and I do run that much clearance, We have seen the GM Crate engines 602 that make 355 horse and we see that with .0006 pin clearance from the factory that the pins will gaul.

Again look at the Mahle pistons as we use a lot of them for street performance and circle track engines those run right at .001 to .0012 clearance and zero issues.

Most pistons come with pins that are .9272 to .9275 but will the same size per set!! And if the pins were .927 I don't think I would have to hone the pin bores.

We took apart an engine from another shop and the Manley pistons the pin bores were to tight and the pin bores were black, I have not check the clearance yet but I would say they are to tight.
Website is up and running
http://hinksonautomotive-cncblocks.com/
Machine shop tour
http://hinksonautomotive-cncblocks.com/shop-tour/
Monthly Specials
http://hinksonautomotive-cncblocks.com/specials/
Soon 55MM babbit cam bearings with 1 hole
CNC BLOCKS
Guru
Guru
 
Posts: 4516
Joined: Thu Jul 01, 2004 5:34 am
Location: NORTHEAST

Re: Piston to pin clearance question

Postby donc » Thu Apr 21, 2011 7:21 am

needforspeed66gt wrote:Image


The setting fixture is explained in this set of instructions.

http://www.sunnen.com/graphics/assets/d ... be80c6.pdf

The sunnen comparator has brass shims on back that can wear sunnen acn send you instructions how to adjust, furtermore using a good mic and setting the ag300 properly or a bore gauge seems to be more accurate than the comparator.
donc
Guru
Guru
 
Posts: 1151
Joined: Sat Dec 04, 2010 9:10 am

Re: Piston to pin clearance question

Postby CNC BLOCKS » Thu Apr 21, 2011 7:36 am

needforspeed66gt wrote:Image


The setting fixture is explained in this set of instructions.

http://www.sunnen.com/graphics/assets/d ... be80c6.pdf


That gauge is for checking the pin end of the rod and seems to be pretty accurarte as we check with our bore gauge when we are done.

Its hard to get a piston square to the face of the AG-300 and we have found a sunnen bore gauge works the best.
Website is up and running
http://hinksonautomotive-cncblocks.com/
Machine shop tour
http://hinksonautomotive-cncblocks.com/shop-tour/
Monthly Specials
http://hinksonautomotive-cncblocks.com/specials/
Soon 55MM babbit cam bearings with 1 hole
CNC BLOCKS
Guru
Guru
 
Posts: 4516
Joined: Thu Jul 01, 2004 5:34 am
Location: NORTHEAST

Re: Piston to pin clearance question

Postby Brian B » Thu Apr 21, 2011 8:00 am

Its hard to get a piston square to the face of the AG-300 and we have found a sunnen bore gauge works the best.[/quote]


Yes it is....it takes some time to get the "feel" for it...more of a pivot and sweep across the fingers..
The AG 300 is the only way I have ever check piston pin bores...20 plus years
Brian B
Dakota Parts Warehouse
The Ferrea Valve Guy
Stocking HYLOMAR
Ask about our Fast Setting Silicone..its fast
Now in stock
5/16 hollow stems
5/16 6000 series SBC
877 235 2832
Brian B
Expert
Expert
 
Posts: 979
Joined: Tue May 04, 2004 5:48 pm
Location: South Dakota

Next

Return to Engine Tech

Who is online

Users browsing this forum: 91stang, Bill MeLater, Bing [Bot], chubbshp, mrriggs, Nefario, RevTheory, Walter R. Malik and 25 guests