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Discussion Starter #1
Going to a 103" build soon on my 07 flhx. If when I check the deck height upon dissassembly of the stock motor, can I assume that it will be the same with the new flat tops? Or do I have to assemble with the new pistons and measure them? I was hoping to save a step. I would like to achive 0 deck on the build.
 

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You can measure the distance from the top of the wrist pin hole to the top of the pistons on both the old piston and the new piston and then calculate the difference.

Example, if your stock piston is .010" below the deck and the new piston is .002" taller from the top of the pin to the top of the piston, it is likely the new piston would be .008" below the deck.
 

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MaxHeadflow
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It takes 2 minutes to slip the piston on the rod, push the pin in then slip the cylinder on and turn the crank so that each piston is at TDC. Don't need to install the rings, clips or O rings.. Wash your cylinders first... Bruce
 

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Measure Twice

I was told by R&R to save time to measure with the old piston (clean top of piston) to save time and they could cut the jugs,cc heads to acheive the .035 squish-quench which would save time . I always measure twice when cutting anything jussayin. Good Luck.
 

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IronButt
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Now if you are not using SE pistons you will find that your TDC will be very close if not spot on. The se line of pistons seem to be on the short side, maybe to help the bolt on guys in the dealership?? Yes measuring the old piston is the fastest way to do what you need to do. I would not however put the piston in the bore with out rings as you may not get a accurate measrment, and as well with out the rings to stablize the piston you may scuff the piston and bore. The piston rings hold the piston stable not the other way around.

Someone that has built plenty of engines may be able to pull that off, but I dont bother it takes so little time to put the rings on , and slip it into the bore. Plus you have to install them anyways so what time are you really saving??
 

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If the machine shop that is boring and decking the cylinders is down the street, I would always recommend assembling and measuring with the newly bored cylinders and new pistons. When the shop is not local, the above method will work.
 

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MaxHeadflow
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"I would not however put the piston in the bore with out rings as you may not get a accurate measrment, and as well with out the rings to stablize the piston you may scuff the piston and bore. The piston rings hold the piston stable not the other way around. "

I typically measure the quench distance at the pin so the rocking has no effect.. It's also a good check for dome clearance (if you got em).

You think that a bare piston is going to scuff the bore more than a one with rings? While on most simple builds you won't have to go back in, installing rings is OK but what if you need to trim the cylinder? IIRC some of the rods are short.

If the cylinders need trimming, I'd definately check this way just to make sure the right amount was removed.

Bruce
 

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IronButt
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Bruce

Not that you are wrong but you have to think that many that read this are not aware of what type of reading they could get if certain info is left out. Better to keep safe. If installed into the cylinders with rings the reading will be the most accurate. That way the avg guy that has never done this will be able to get a true reading and not remove too much from his cylinders.
 

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MaxHeadflow
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You are right, maybe I'm making too many assumptions about the abilites of those on this forum. Anyway I'm NOT advocating to NOT checking on final assembly (with the rings) again. Can never check too much. Bruce
 

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lets say we have an 07 cvo 4" bore heads are setup for 10.5! what would the compression be if if the piston is say .012 down in the hole??
Thanks Happy
 

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Motor Machinist
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If I am setting up a top end, it is more important to take the quench into consideration rather then the compression, the 0 deck height allows for a adjustable quench using the different thickness head gaskets that are available.
The compression can be adjusted by changing the closing cam timing of the intake valve.
 

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MaxHeadflow
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Happy

The CR would drop about 0.2 or you'd be at about 10.3 to 1. The worst part is that if ruinning a 0.053 HG you squish would be about 0.065..

Jurneyman,

IMO, quech (squish) is more important than CR. Remember that using the intake close to correct compression ratio, only does so for RPMs below the Tq peak. When the tq starts to peak, the pipes and intake are starting to work for you and the corrected CR at that RPM is going up. The good thing is that as the motor spins faster, there is more tubulance in the combustion chamber which helps the mix and reduces ping at higher RPM. Keeping the low end corrected CR won't help an upper RPM ping.. I most cases you don't have to worry about it until the CR is over 11 to 1. At least on what I've seen with SoCal gas....

Bruce
 

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what i am saying or asking is if you had a set of heads made up at 10.5 and the porter is assuming your have 0 deck height he sets the cc up for it. then you take the motor apart and discover you have .012 down in the hole.. you will have a problem no matter what cam is used? i would never put it together that way myself if i spent the money for a 10.5 build and had the cams also for that build..
Happy
 

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If you new pistons are still that much below deck height with the cylinder torqued properly, you are going to have to take some off the bottom of the cylinder. .012 sounds like a lot, I would have someone who knows what he is doing check it out before haveing that much chopped off the bottom. (taken off)
 

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MaxHeadflow
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happyman said:
what i am saying or asking is if you had a set of heads made up at 10.5 and the porter is assuming your have 0 deck height he sets the cc up for it. then you take the motor apart and discover you have .012 down in the hole.. you will have a problem no matter what cam is used? i would never put it together that way myself if i spent the money for a 10.5 build and had the cams also for that build..
Happy
Then your quench would be 0.042 assuming he specified 0.030 cometics and your cr would still be 10.3 to 1. Not sure you'd have any problem with the build. Moght be a little soft on the low end or ping slightly depending on the corrected CR. 0.012 may not make that much difference if the quench ended up at 0.042.

Bruce
 

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IronButt
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Would like to add something here, I have seen where many shops install a thicker head gasket to lower compression as they where concerned about ign ping. The thicker head gasket can be more liklely to induce ping due to a poor squish.

You can machine either the top or bottom of a cylinder. Most pull from the bottom, but it does not matter really. Reduce height is ok the only issue that you could have is if you have to remove a huge amount and the dowel pins fail to allow the head to crush the gasket to spec, that is a easy fix either by measurment, or shortening the aligment pins.

We just checked a 07 96 inch yesterday and the front piston was .001 down and the rear was less than a .001 . Did not mess with the cylinder at all, no need to.
 

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mostly curious here . am looking at doing heads and camsedt on a 110" cvo and hace read a nasty rumor they have been found to have the issue of the piston being too far down the hole.. but then you know whT THEY SAY ABOUT RUMORS TOO.
Happy
 
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