Re-ring pistons? 107 kit?

2953 Views 12 Replies 6 Participants Last post by ironmark, Mar 13, 2015

modot66

Discussion Starter · Mar 9, 2015

i've got my heads off for stage 1 work and am putting in cams + bumping compression to 10.25-1 so right now my top end is off the bike. i have about 21,000 miles on the bike and haven't had issues with oil consumption or anything. buuuut...

i am thinking while i am waiting for my heads (was quoted a 3 week wait) does it make sense to pull jugs, hone, clean pistons, re-ring, and put all new base gaskets in? my thinking is while i'm waiting and this far might not be a bad idea to freshen it up.

of course then i start thinking "well why not go to a 107 then?" i don't have bottom end work done and don't want a super hot bike with loud train noise. i could get 107 juggs/pistons for $650 so there's an additional cost. i'm not entirely convinced a 103 to 107 is worth it.

anyone have any thoughts?

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Desertwndrr

· #2 · Mar 9, 2015 (Edited)

What cams? What headwork?

The reason that I ask is because the valve reliefs in the stock cast pistons may be a bit small if you are going to larger valves.

103 to 107 isn't that much of a difference until you factor in that most 107 builds have bumped up compression. You're likely going with a flattop piston, .030 head gasket and maybe a touch off the heads to get to 10.25. Am I right? That being the case, flattop to flattop 103 to 107 won't matter much.

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modot66

Discussion Starter · #3 · Mar 9, 2015

getting 1.9 intake valve so should work with stock pistons. going with drago 565 cam

i'm bumping compression either way from 9.6 to 10.25

i figured about an extra $100-150 for new base gaskets/rings, etc as opposed to $650 for 107 pistons, cylinders, rings, etc.

trying to decide if the pros/cons of a 107 are worth the extra cash

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modot66

Discussion Starter · #4 · Mar 9, 2015

"You're likely going with a flattop piston, .030 head gasket and maybe a touch off the heads to get to 10.25"

spot on!

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Desertwndrr

· #5 · Mar 9, 2015

Not really worth going to 107 unless you have to. There are no base gaskets, instead there are O-rings. Personally I'd just leave it and not pull it apart for new rings. If you ever do start to leak down the road, then I'd bump it to 107 and rering it. Plenty of my friends are running upwards of 50-100,000 miles with no issues of leaking and burning oil. Besides, to rering it you'd have to rehone or deglaze the cylinders and then you are looking at having to break it all in again. Save the $$.

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JacktheBagger

· #6 · Mar 10, 2015

With that few miles ,you arent even broke in good . I wud leave it alone . If ya just have to go up , go with a 117 .

JtB

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ironmark

· #7 · Mar 10, 2015

Your top end is in good shape so why put the extra money into it if your stock pistons work.
Even with a .030 head gasket and a cam upgrade you will only get 10.15:1 static compression and 9.57:1 corrected compression which is right where you want it to be anyways.
Since I didn't know which cam you are using I just used the Woods TW222 as the cam in the calculation.
You can figure out what your compression is going to be by going to http://www.bigboyzheadporting.com and click on calculators.

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124shark

· #8 · Mar 10, 2015

Back to back testing on a 103 vs a 107 no changes other that increase in CI as head gasket was .027 to a .040 to keep it as close as we could. Andrews 54 dd 2-1

103 94 hp 108 tq

107 97 hp and 112 tq.. So end of the day unless you have to go larger the gains are not going to amount to much. Now same build but getting the comp ratio to 10.2

99 hp 116 tq .. Again gains are small for invested amount.

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Slider1156

· #9 · Mar 13, 2015

So I have been advised by my indy mechanic if you pull off the heads you should replace the o rings on the cylinder base. it sure would suck to get an oil leak after doing all that work.

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modot66

Discussion Starter · #10 · Mar 13, 2015

i was wondering this myself so called frank at dragos and he said to pull the cylinder up and if the gaskets look good then no reason to switch. i don't want to have to break in new rings or risk getting debris in the cylinder and damaging the cylinder wall so if they look ok i will just put heads on and run em.

Slider1156 said:
So I have been advised by my indy mechanic if you pull off the heads you should replace the o rings on the cylinder base. it sure would suck to get an oil leak after doing all that work.

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Desertwndrr

· #11 · Mar 13, 2015

I wouldn't pull them up at all. Doing so may break a seal and cause a leak. If the bases of the cylinders are not leaking then do not disturb them. Bolt he heads on and run the piss out of it.

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modot66

Discussion Starter · #12 · Mar 13, 2015

yep. i was a little worried cause the front cylinder moved a little when i pulled the head, but i don't think it was enough to cause any damage. it just rocked back and forth about an 1/8". the rear cylinder stayed down tight.

later today i'm gonna cut some 1/2" pvc pipe and tighten the cylinders down a bit until my heads come in.

Desertwndrr said:
I wouldn't pull them up at all. Doing so may break a seal and cause a leak. If the bases of the cylinders are not leaking then do not disturb them. Bolt he heads on and run the piss out of it.

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ironmark

· #13 · Mar 13, 2015

Desertwndrr said:
I wouldn't pull them up at all. Doing so may break a seal and cause a leak. If the bases of the cylinders are not leaking then do not disturb them. Bolt he heads on and run the piss out of it.

The base seals are just big rubber O-rings and they should not be stuck to the crankcase at all because they are lubed with oil on installation. You don't need to worry about the seal like you would with a fiber gasket.
There is no need to tighten down the cylinder while your waiting for the heads unless you are turning the engine over.

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