Some just like it tight!
Engine Build Time
Stellar HDF Member
Joined: May 2009
Posts: 2,066
Likes: 97
From: Northern VA
Matt I read a lot on this subject then backed off when AMS told me no worries. Several things have big impacts on whether you decide to clay or not. One of the biggest reasons I did a 107" BB was to get the pistons with bigger valve reliefs - these pistons(CP) are used with much bigger cams than I chose, so confidence there. Also, the valve lift at TDC Compression is the # that counts, so if you pick a cam with a relative normal # there it helps. Then of course the squish/quench clearance as you have brought up, if you use a more common amount say .035" to .040" then less worries. Lastly, and probably most importantly is the shops' experience doing your heads and cylinders - no telling how many motor builds AMS has done and Eric did not flinch at all when I brought this subject up even with shaving .032" off my heads for compression. Of course the conservative thing to do is to go ahead and clay it, just adds more time.... And at my pace......
Here is a reference that is interesting:
http://www.nrhsperformance.com/tech_valvetopiston.shtml
Here is a reference that is interesting:
http://www.nrhsperformance.com/tech_valvetopiston.shtml
I just never could wrap my head around what happens at this stage. You had your heads shaved to get a certain CR. Doesn't the pistons depth in the hole and the head gasket size affect the CR too? So if the piston + HG is now 0.030 vs. 0.035 previous, any CR changes there? Minor? And if you find the piston does contact a valve at this point in a build, it seems the only recourse for a DIY'er is to increase the head gasket thickness, which also would lessen your CR.
I'm sure these are simple questions for those that do this for a living. .always confused me though. Good to know, at the very least, if I buy a kit, etc, that it appears most of the clearances are all worked out so I can install at home without finding a machine shop to bail me out.
Can one of the prior posters, srt8 or soft, explain the "measure and add it all up" reference(s) versus claying? Would be worth knowing to save a head gasket. If the heads have been shaved does this still work?
Matt
Last edited by mattVA; Mar 12, 2014 at 06:39 AM.
Thread Starter
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Elite HDF Member
Joined: Sep 2012
Posts: 3,791
Likes: 57
From: N Texas
As for my particular build, the unexpected .003" in the hole vs .008" caused a compression bump of .11, so I went from an expected CR of 10.51:1 to 10.62:1. To increase the squish/quench I have ordered new Cometic .030" HGs and that will bring the compression back down to 10.55:1 which is fine for me.
I tried hard to find the Cometic HGs cheaper from anywhere but had no luck and had to order directly from Cometic again. I don't know why but Cometic HGs for a 107" build are not stocked it seems, I think that the BB providers have them but not the Harley sites, Ebay, Amazon, etc...
Ordered on Monday, hopefully they will show up on Thursday or Friday and I can get back to work.
I tried hard to find the Cometic HGs cheaper from anywhere but had no luck and had to order directly from Cometic again. I don't know why but Cometic HGs for a 107" build are not stocked it seems, I think that the BB providers have them but not the Harley sites, Ebay, Amazon, etc...
Ordered on Monday, hopefully they will show up on Thursday or Friday and I can get back to work.
Thread Starter
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Elite HDF Member
Joined: Sep 2012
Posts: 3,791
Likes: 57
From: N Texas
Started to clean up my rockers and to replace the Breather baffles and filter elements. The baffles have a gasket on top and below that do not come out very cleanly and require some careful scraping and Scotch-Brite.
There has been a fair amount of discussions about enlarging the breather drain holes in the rockers. Stock size is .060" and people have suggested enlarging them from .089" up to .125" (1/8"). I think .125" is a significant enlargement and I find it a bit hard to make that big of a change, planning on .09375 which is a 3/32 bit.
There has been a fair amount of discussions about enlarging the breather drain holes in the rockers. Stock size is .060" and people have suggested enlarging them from .089" up to .125" (1/8"). I think .125" is a significant enlargement and I find it a bit hard to make that big of a change, planning on .09375 which is a 3/32 bit.
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Elite HDF Member
Joined: Sep 2012
Posts: 3,791
Likes: 57
From: N Texas
Checked my 4 end plays at .009" up to .011" so I will leave it as is - my bike only has about 4000 miles on it so has not developed much end play yet.
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Road Master
Joined: Apr 2012
Posts: 1,096
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From: San Jose
You're close to firing it Up!
