Boring factory 107" cylinders

[Ohio HD]

You need 1.143" compression height x what ever bore you're looking for.

[harpwrench]

Screamin eagle piston kit for converting 107 to 114 is part number 21900084, 11:1 compression, I'm guessing they sell head gaskets as well

Edit sorry now I see you're asking about 117 pistons

[Ohio HD]

And if you bore to 4.125" you can use CP BHM8117-FT pistons.

[Adam76]

And if you bore to 4.125" you can use CP BHM8117-FT pistons.

Thanks Ohio, I just need to know if it's still considered safe to bore out stock 107 cylinders to 4.125" ??
Or are youtalking about factory 114" cylinders?

Thanks  sorry for the confusion.

[Ohio HD]

See reply number 69.

https://harleytechtalk.com/htt/index.php/topic,119199.msg1429456.html#msg1429456

[Adam76]

See reply number 69.

https://harleytechtalk.com/htt/index.php/topic,119199.msg1429456.html#msg1429456

Great, Thanks.

So 114" / 117" cylinders
BHM8117-FT pistons.
On a 107"  4.375" stroke bottom end.

So have I got that right now? 
Cheers

[Adam76]

Screamin eagle piston kit for converting 107 to 114 is part number 21900084, 11:1 compression, I'm guessing they sell head gaskets as well

Edit sorry now I see you're asking about 117 pistons

Thanks harpwrench,

114" / 117" it doesn't really matter as long as I can match the correct pistons, with the correct cylinders and the correct size MLS Cometic head gaskets for the bore size. Which seems to be very confusing.

[rigidthumper]

Have them bored for your CP 4.125 pistons, to make your 107 a 117.

[Ohio HD]

[Adam76]

And if you bore to 4.125" you can use CP BHM8117-FT pistons.

Thanks Ohio. Yes I understand that the pistons listed above are the correct ones used to bore my factory 107" cylinders out to 117"

But both you and a few others, including Rigidthumper have advised me to use "take off" 114" or 117" Cylinders instead...

So if I use a set of factory "114" cylinders on my 4.375" stroke motor, what exact 4.125" bore pistons do I need??

Apologies for the repeated question, but your posts #77 and #79 contradict each other. 

Not trying to be a pain in the ass, I really appreciate your efforts in trying to help me out here. 

[Adam76]

I'd get a set of 114/117 take off cylinders if you are going to 4.125.

No problem, sounds good.

But which 4.125" pistons exactly are are going to work with the 114" factory cylinders you've suggested I put onto my 107" bottom end?

Man this is ridiculously confusing. Sorry.   

[Ohio HD]

And if you bore to 4.125" you can use CP BHM8117-FT pistons.

Thanks Ohio. Yes I understand that the pistons above are the correct ones used to bore my factory 107" cylinders out to 117" and I'm happy to do that if there's enough thickness in the cyl wall.... But both you and a few others, including Rigidthumper have advised me to use "take off" 114" or 117" Cylinders instead...

So if I use a set of factory "114" cylinders on my 4.375" stroke motor, what exact 4.125" bore pistons do I need??

Apologies for the repeated question, but your posts #77 and #79 contradict each other. 

Not trying to be a pain in the ass, I really appreciate your efforts in trying to help me out here. 

They do not contradict each other.

Post #77 I said to use the pistons I've mentioned a few times.
Post #79 I said to see the post #69 by Ridgedthumper saying use 114 / 117 OEM takeoffs.

How does that contradict? 

The CP piston number that answers your question I've posted the answer twice already.

Then you must bore the cylinders to 4.125". It's simple!   

[Adam76]

And if you bore to 4.125" you can use CP BHM8117-FT pistons.

Thanks Ohio. Yes I understand that the pistons above are the correct ones used to bore my factory 107" cylinders out to 117" and I'm happy to do that if there's enough thickness in the cyl wall.... But both you and a few others, including Rigidthumper have advised me to use "take off" 114" or 117" Cylinders instead...

So if I use a set of factory "114" cylinders on my 4.375" stroke motor, what exact 4.125" bore pistons do I need??

Apologies for the repeated question, but your posts #77 and #79 contradict each other. 

Not trying to be a pain in the ass, I really appreciate your efforts in trying to help me out here. 

They do not contradict each other.

Post #77 I said to use the pistons I've mentioned a few times.
Post #79 I said to see the post #69 by Ridgedthumper saying use 114 / 117 OEM takeoffs.

How does that contradict? 

The CP piston number that answers your question I've posted the answer twice already.

Then you must bore the cylinders to 4.125". It's simple!   

Sorry, my question should have been -- if I used a set of  114" cylinders like Rigidthumper has suggested, what pistons are compatible with the cylinders that are now .070" taller on my 4.375" stroke motor  ?

Thats' all I was trying to work out.

Thanks

[Ohio HD]

harpwrench already answered in post #76. To use 114 cylinders (bored 4.075", standard 114" cylinders you use what he said to use SE 21900084 pistons.

I said, now the third time, use CP BHM8117-FT for these same cylinders and bored to 4.125".

[Adam76]

harpwrench already answered in post #76. To use 114 cylinders (bored 4.075", standard 114" cylinders you use what he said to use SE 21900084 pistons.

I said, now the third time, use CP BHM8117-FT for these same cylinders and bored to 4.125".

Ok, I thank you Sir, for the third time. 

Use 114" cylinders with the CP BHM8117-FT pistons to get me to 117"



Pheeew. That was painful.

[rigidthumper]

The 107 and the 114/117 cylinders are the same height. 107 cylinders have had issues taking them to 4 1/8". The 114/117 cylinders have more meat in the liner, making them the better choice to bore to 4.125. Actually, they can go to 4.180 to make a 120" if you wish.
LINK

[Ohio HD]

The best example that I could find to show stoke change, and compression height change in a piston is this link to a performance Ford motor site. The basics stay the same if you're thinking car or motorcycle.

We'll use figure 1 as a 107" motor and figure 2 as a 114" motor.

Compression height is the distance of the piston pin to the top of the piston flat, not including any dome.

When the stroke increases as in a 114" motor, something has to change to allow the piston to stay within the cylinder and not extend outside the bore. What changes is the compression height of the piston, the pin center to piston top.

What piston manufacturers do to mix a shorter stroke to a larger bore as when 114" cylinders are used on a 107" motor. They make a custom piston in the bore required (could be a stock 114" motor bore, or in a desired 4.125" bore or other bore size) with a compression height (pin location in the piston) to match the stroke being used.

All of this is based on using cylinders that are the same height. And we know the 107", 114" and 117" motors use the same OEM height cylinder from the factory. There are other things that effect compression height, rod length, cylinder length and we covered stroke. But in the case of M8 107", 114" and 117" motors, the rod length and cylinder length all stay the same.





Example of motor before and after a stroke increase.

[kd]

      As usual, you nailed it.  That should be easy enough for Adam or anyone else considering this engine modification to understand.

[Ohio HD]

All of the motor component swaps can be confusing. And just because I've been around it for a lot of years doesn't mean it's something everyone knows the details surrounding the changes. I could have been more explanative in my posts.

[Tail Ridr]

The 107 and the 114/117 cylinders are the same height. 107 cylinders have had issues taking them to 4 1/8". The 114/117 cylinders have more meat in the liner, making them the better choice to bore to 4.125. Actually, they can go to 4.180 to make a 120" if you wish.
LINK

If I were to buy a set of cylinders to bore, I would surely go to the 120, like Suburban's kit, and likely a different cam. (But that's another story)

[Adam76]

The 107 and the 114/117 cylinders are the same height.

Thanks, this was the detail that was tripping me up.
Thanks again for clarifying. 

[Adam76]

All of the motor component swaps can be confusing. And just because I've been around it for a lot of years doesn't mean it's something everyone knows the details surrounding the changes. I could have been more explanative in my posts.

Hey no worries, thanks for your help and patience.... I can be a bit of a slow learner at times but I totally get it now. 

[Adam76]

The 107 and the 114/117 cylinders are the same height. 107 cylinders have had issues taking them to 4 1/8". The 114/117 cylinders have more meat in the liner, making them the better choice to bore to 4.125. Actually, they can go to 4.180 to make a 120" if you wish.
LINK

If I were to buy a set of cylinders to bore, I would surely go to the 120, like Suburban's kit, and likely a different cam. (But that's another story)

Thanks guys,  I'm probably going to stay at 117" because I only have 5.5 injectors..... Not sure what size injectors the 120" would need.

I just picked up a set of 114" take off cylinders from a 2021 low rider,  so I'm half way there 

Now I just have to order the pistons and pick a camshaft.....

[Adam76]

I have sourced a set of take off 114" cylinders and have just ordered the CP BHM8117-FT pistons. And the Star 30-30 camshaft.

I have a competent machinist lined up to bore and hone with torque plates and I should be good to go.

How far are the pistons usually down the hole on these M8 motors?
Looking at a set of  Cometic Head and base gaskets of .010" base and .030" head gaskets. But will probably wait until mock up just to be sure.

[kd]

I have sourced a set of take off 114" cylinders and have just ordered the CP BHM8117-FT pistons. And the Star 30-30 camshaft.

I have a competent machinist lined up to bore and hone with torque plates and I should be good to go.

How far are the pistons usually down the hole on these M8 motors?
Looking at a set of  Cometic Head and base gaskets of .010" base and .030" head gaskets. But will probably wait until mock up just to be sure.

.

By all means wait and mock it up.  Gaskets can be ordered and received quick by mail so no worries.  There's even a possibility you could need to face the barrels to get things in reach for your gasket choices. Taking care of the details usually pays dividends.