I am rebuilding my 12abp with Atkins seals per Judge Ito. He prefers these for nitrous applications, so Atkins it is. I found a post where he recommends a clearance of .003 for sideseal to corner seal clearance. I broke out the old feeler gauges to see what I'm workin with. My engine is brand new fresh with about 1000 miles on it, but it was built with carbons, so I tore her down to install more reliable guts. My Chilton book says if the seal clearance is .0159 or greater, you MUST replace the seal. It then goes on to say that if the clearance is .0069 or greater, the performance will decline prematurely. I measured my seals, and the measure anywhere from .005 to .008 clearance. I know Ito says .003 is the minimum gap allowed with nitrous to account for growth under heat, but I'm not sure if this wider gap I have is acceptable. What are the thoughts? Is it normal to see such large clearance after 1000 miles? I dont know where the clearances were when it was new (I didnt not assemble it initially). I would assume this motor would have been set up on the tight side since it was origionally intended to be use N/A (hence the carbon seals).

 

What corner seals are you using stock or solids? And were they new when the motor was rebuilt? I personnally prefer solids when it comes to nitrous.

 

[quote name='13BTNOS' date='Jun 22 2005, 11:10 AM']What corner seals are you using stock or solids? And were they new when the motor was rebuilt? I personnally prefer solids when it comes to nitrous.


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The engine had brand new stock corner seals with the rubber supports. I will be switching to solid corner seals when I add the Atkins seals.

 

[quote name='Stock Josh' date='Jun 22 2005, 01:10 PM']The engine had brand new stock corner seals with the rubber supports. I will be switching to solid corner seals when I add the Atkins seals.


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Get the solids in there and then recheck the clearances and see if there is a difference. Side seals like to cut a grove on the corner seal and sometimes that's enough to make a difference.

 

Well, I found a post where Ito recommends a gap of .003 but no larger. So I guess that answers that question. Sorry about the redundant question guys.

 

the more clearance you have the more the compression will escape, it is less so important as the rpm climb. anywhere from .100-.300 is good goign passed .500 you will notice a compression drop which equates to some power loss.

 

[quote name='13BTNOS' date='Jun 22 2005, 01:43 PM']Side seals like to cut a grove on the corner seal and sometimes that's enough to make a difference.


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So file the spring dent out of the other side, then flip the corner seals over (so the side seal rides on the un-grooved side) and reuse.



Simple.



- The Cheapass

 

When I clearence side seals, here is what I do. I take a measurement and mark, then on a tiny bench grinder I get close. Then using a diamond file I do the rest by hand till I'm almost where I want to be. I then use 2500 grit to polish in direction of movement, I put the smallest bevel as well, both these things keep me from ever having suffered a sticking side seal. (I have noticed less wear on corner seals from this as well) I shoot for no more .003 on most apps. Tighter on some, it all depends. That's what works for me. Hope it helps.

 

i believe the renesis side seal clearance is considerably more than the 13b NA or 12a? i think this is to provide better high RPM operation. i guess it depends on how the engine will be used. i would think a BP 12a would see mostly high rev operation, especially if it's a race engine, in which case it's not that big of an issue if you are a little more than .003, but you mentioned nitrous so maybe you have some other plans...