Boring factory 107" cylinders

[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.

.

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.

Thanks, I thought so.

I was just curious to see what the "standard" was for the M8 motors as far as how far down the hole the pistons usually are.

I'm hoping to get to s close to zero deck height as possible just by using a thinner cylinder BASE gasket rather than having to face the barrels...

Cheers

[rigidthumper]

The pistons you've chosen will put the deck height ~.004" down with standard length M8 cylinders and a .010" base gasket. 10.7:1 CR with a .040" HG, 10.9:1 with a .030" HG.
Star 30-30 designed for stock compression, 10.17:1 corrected.
Star 30-30 with a .040" head gasket would be 10.35:1 corrected.
Star 30-30 with a .030" head gasket would be 10.56:1 corrected.

[Adam76]

The pistons you've chosen will put the deck height ~.004" down with standard length M8 cylinders and a .010" base gasket. 10.7:1 CR with a .040" HG, 10.9:1 with a .030" HG.
Star 30-30 designed for stock compression, 10.17:1 corrected.
Star 30-30 with a .040" head gasket would be 10.35:1 corrected.
Star 30-30 with a .030" head gasket would be 10.56:1 corrected.

Thanks, so with your calculations above it I get it right, I should use

.014" cyl base gaskets to give me zero deck height.

And .030" head gasket to give me .030" squish?

Thanks

[FXDBI]

The pistons you've chosen will put the deck height ~.004" down with standard length M8 cylinders and a .010" base gasket. 10.7:1 CR with a .040" HG, 10.9:1 with a .030" HG.
Star 30-30 designed for stock compression, 10.17:1 corrected.
Star 30-30 with a .040" head gasket would be 10.35:1 corrected.
Star 30-30 with a .030" head gasket would be 10.56:1 corrected.

Thanks, so with your calculations above it I get it right, I should use

.014" cyl base gaskets to give me zero deck height.

And .030" head gasket to give me .030" squish?

Thanks

.006 base gasket to get 0 a .014 will give you .008.   Bob

[Adam76]

The pistons you've chosen will put the deck height ~.004" down with standard length M8 cylinders and a .010" base gasket. 10.7:1 CR with a .040" HG, 10.9:1 with a .030" HG.
Star 30-30 designed for stock compression, 10.17:1 corrected.
Star 30-30 with a .040" head gasket would be 10.35:1 corrected.
Star 30-30 with a .030" head gasket would be 10.56:1 corrected.

Thanks, so with your calculations above it I get it right, I should use

.014" cyl base gaskets to give me zero deck height.

And .030" head gasket to give me .030" squish?

Thanks

.006 base gasket to get 0 a .014 will give you .008.   Bob

Thanks Bob. I'm not sure Cometic make a .006" base gasket? Lowest I can find is .010"

[kd]

The pistons you've chosen will put the deck height ~.004" down with standard length M8 cylinders and a .010" base gasket. 10.7:1 CR with a .040" HG, 10.9:1 with a .030" HG.
Star 30-30 designed for stock compression, 10.17:1 corrected.
Star 30-30 with a .040" head gasket would be 10.35:1 corrected.
Star 30-30 with a .030" head gasket would be 10.56:1 corrected.

Thanks, so with your calculations above it I get it right, I should use

.014" cyl base gaskets to give me zero deck height.

And .030" head gasket to give me .030" squish?

Thanks

.006 base gasket to get 0 a .014 will give you .008.   Bob

Thanks Bob. I'm not sure Cometic make a .006" base gasket? Lowest I can find is .010"

I do believe they make MLS head gaskets in .027.  That will give you .031 quench (squish).  I'd say that's barely negligible and good enough for the girls I go out with.     Wait until you mock up before you order any base and head gaskets. 

BTW, cleaning up the barrel gasket surfaces isn't a bad thing.  We're talking .004" here.  Pull out your feeler gauges and you will see .004 is just enough to ensure the gasket surfaces are smooth and true.

[Adam76]

The pistons you've chosen will put the deck height ~.004" down with standard length M8 cylinders and a .010" base gasket. 10.7:1 CR with a .040" HG, 10.9:1 with a .030" HG.
Star 30-30 designed for stock compression, 10.17:1 corrected.
Star 30-30 with a .040" head gasket would be 10.35:1 corrected.
Star 30-30 with a .030" head gasket would be 10.56:1 corrected.

Thanks, so with your calculations above it I get it right, I should use

.014" cyl base gaskets to give me zero deck height.

And .030" head gasket to give me .030" squish?

Thanks

.006 base gasket to get 0 a .014 will give you .008.   Bob

Thanks Bob. I'm not sure Cometic make a .006" base gasket? Lowest I can find is .010"

I do believe they make MLS head gaskets in .027.  That will give you .031 quench (squish).  I'd say that's barely negligible and good enough for the girls I go out with.     Wait until you mock up before you order any base and head gaskets. 

BTW, cleaning up the barrel gasket surfaces isn't a bad thing.  We're talking .004" here.  Pull out your feeler gauges and you will see .004 is just enough to ensure the gasket surfaces are smooth and true.

Thanks kd, so you recommend taking a few thou of the base of the barrels as well as the tops of the barrels to ensure nice flat smooth surface?

Of course depending on how far down the hole the pistons are 

[kd]

The pistons you've chosen will put the deck height ~.004" down with standard length M8 cylinders and a .010" base gasket. 10.7:1 CR with a .040" HG, 10.9:1 with a .030" HG.
Star 30-30 designed for stock compression, 10.17:1 corrected.
Star 30-30 with a .040" head gasket would be 10.35:1 corrected.
Star 30-30 with a .030" head gasket would be 10.56:1 corrected.

Thanks, so with your calculations above it I get it right, I should use

.014" cyl base gaskets to give me zero deck height.

And .030" head gasket to give me .030" squish?

Thanks

.006 base gasket to get 0 a .014 will give you .008.   Bob

Thanks Bob. I'm not sure Cometic make a .006" base gasket? Lowest I can find is .010"

I do believe they make MLS head gaskets in .027.  That will give you .031 quench (squish).  I'd say that's barely negligible and good enough for the girls I go out with.     Wait until you mock up before you order any base and head gaskets. 

BTW, cleaning up the barrel gasket surfaces isn't a bad thing.  We're talking .004" here.  Pull out your feeler gauges and you will see .004 is just enough to ensure the gasket surfaces are smooth and true.

Thanks kd, so you recommend taking a few thou of the base of the barrels as well as the tops of the barrels to ensure nice flat smooth surface?

Of course depending on how far down the hole the pistons are 

Because it's only .004 doing the top and bottom will be a very fine .002 each.  You can opt for top "or" the bottom for the full .004".  With so little coming off, if you chose the bottom it shouldn't effect the intake manifold fit. Taking it off the top doesn't change anything but the piston deck height and it's probably cheaper doing one or the other as it's only one operation per cylinder. It's a decent option for an OCD build that may allow you to access common gaskets.  Believe me, I know how that OCD stuff works.    You'll get your zero deck and hopefully can manage the .030 head gasket you desire. 

Now that you are familiar with the Big Boyz calculators you will have to determine the head cc you need to satisfy the correct compression for the cam you chose or choose. You may be good where you are at with zero deck.  It's part of the planning process and journey that  never seems to end, but it will, with a well put together combination. 

[Ohio HD]

Adam, I agree with what rigidthumper said, my math and not measuring the piston should be 0.004" in the cylinder. I'm of the mind that the 0.004" won't kill anything. But I would ask Cometic as KD suggested for an MLS head gasket 0.026" thick. That would get you to zero deck if everything measures as we think it will. Even if you leave it at 0.004", and use an 0.030" head gasket, it's not going to mean all that much performance wise. At least not through the midrange. I let my 124" Twin Cam go at 0.035" squish. For a street motor, that's still much better than OEM. 

I've read a lot of good about the 30-30 cams, just haven't seen the results. But George Bryce puts out some quality parts. I'd give them a try. 


Below is how I come up with the piston depth data. We just use the known design and some OEM measured part dimensions of the parts. But all parts have a tolerance, so it could be a little more or less. That's why measuring should be a must.


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[Adam76]

Thanks kd and Ohio, really appreciate the details and information you posted.

Super helpful. 

[Adam76]

The pistons you've chosen will put the deck height ~.004" down with standard length M8 cylinders and a .010" base gasket. 10.7:1 CR with a .040" HG, 10.9:1 with a .030" HG.
Star 30-30 designed for stock compression, 10.17:1 corrected.
Star 30-30 with a .040" head gasket would be 10.35:1 corrected.
Star 30-30 with a .030" head gasket would be 10.56:1 corrected.

This has me worried, as I was hoping to get close to zero deck height and use a .030" head gasket for good squish.... But now that looks like it's too much compression?

My calculator has me at 11.15 static and with the 30-30 cam's intake close of 25* corrected comp is 10.8  /  233 ccp. I'm thinking that might be much too high...

I've reached out to George Bryce to get his opinion on the compression limits of the 30-30 cam in a 117".

[Adam76]

The pistons you've chosen will put the deck height ~.004" down with standard length M8 cylinders and a .010" base gasket. 10.7:1 CR with a .040" HG, 10.9:1 with a .030" HG.
Star 30-30 designed for stock compression, 10.17:1 corrected.
Star 30-30 with a .040" head gasket would be 10.35:1 corrected.
Star 30-30 with a .030" head gasket would be 10.56:1 corrected.

This has me worried, as I was hoping to get close to zero deck height and use a .030" head gasket for good squish.... But now that looks like it's too much compression?

My calculator -- with the pistons .007" down -- has me at 11 static and with the 30-30 cam's intake close of 25* corrected comp is 10.68  /  230 ccp. I'm thinking that might be much too high...

I've reached out to George Bryce to get his opinion on the compression limits of the 30-30 cam in a 117".

[Ohio HD]

I get pretty close to what Rigidthumper gets.

[Deye76]

Bryce says anywhere between 10 & 11 corrected is "perfect".

[kd]

Bryce says anywhere between 10 & 11 corrected is "perfect".

If that's the answer Adam gets back from George, he'll be in the game.  Being near the upper level will bring in the torque earlier (which I believe is the stated goal) and will require attention to a good tune.  With the extra compression, the .030 quench will up the combustion turbulence and help defend against it becoming a ping machine.

[Adam76]

Bryce says anywhere between 10 & 11 corrected is "perfect".

If that's the answer Adam gets back from George, he'll be in the game.  Being near the upper level will bring in the torque earlier (which I believe is the stated goal) and will require attention to a good tune.  With the extra compression, the .030 quench will up the combustion turbulence and help defend against it becoming a ping machine.

Yes, thanks guys. 
Bryce says 11:1 comp is fine.
He advised on using a .040" head gasket to allow for greater piston to head clearance and trapping more air in to the chamber etc.

Plan is
1. Measure deck height
2. Mill bottom of pistons approx .005" to get closer to zero deck height
3. Use a .010" base gasket
4. CC heads just to make sure they are not too far off the STD 86.5cc
5. Use a .040" head gasket
6. Full custom tune on the dyno

[kd]

Well it sounds like it's coming together nicely. You won't be sorry that you took care of the details before diving in.

[JSD]

Adam you say mill bottom of pistons? Do you mean cylinders? 

[Adam76]

Adam you say mill bottom of pistons? Do you mean cylinders?

Yes, sorry.... typo. 

[Adam76]

Interestingly,  I got this info from George Bryce himself regarding the use of the Star 30-30 cam in my build...

I use .040 piston to head clearance   
Close but not too close. The would idea is to let more air in (30-30) cam to trap more mixture (25) closing to add cylinder pressure to make more power.

Looks like if I can get zero deck height, I'll go with a .040" HG.  Interesting,  as I always thought .030"- .035" was the idea lsquish.  Learn something new every day

[JSD]

I would not go above .038". But Star knows 

[VernDiesel]

Adam looking forward to your results. I have a softail stage 3 107 to 114. 11-1 SE-498 cam S&S Super Street 2-1 with Cat & SE Pro tuner.  It made 116/116.  Since then I added Fueling oil tank breather & a larger Db reducer. Then won a free dyno pull. It pulled 118/122. It picked up some sound volume but is not loud.  Bike still seems to be on point in every way. Part of me hates to mess with it. Been happy with it for over 3 years and 37k but now am trying to get more. 

Had wanted a 139ci but all considered have decided against it. Am & have considered a 128ci build. Really nice CP pistons, jugs, still its some coin.  But am also considered what I could do with existing jugs and Star's new F35A cam. Thinking having Wards port my intake. I'd gut the cat and swap to PV tuner.

George say's the F35A is designed to fit in a stock engine. It closes 10 degrees later than the 30 30 at 35 after bottom, has 572 lift, and is designed for 10.5 to 11.5-1.

We will perform leak down test & check crank runout. Just a hot rodder and ever learning hobbyist here. So this thread sparked me. If we decide to pull the heads and jugs to re ring freshen cylinders and make sure everything is square and seals good. Well then ridgidthumper goes and posts you could go 4.180 make it a 120ci and posts a link. $375 a piston isn't much. It would already come with fresh rings. Not much more to bore it. Only it says 12.0-1. 11.5-1 sounds safer and meets George's listing. Not sure I fully follow all these measurements and know all my options here. I'd be the assistant anyway but would be interested in what you all might suggest.

"He (Bryce) advised on using a .040" head gasket to allow for greater piston to head clearance and trapping more air in to the chamber etc."  I thought that was interesting.  George thinks deep.

[Adam76]

Adam looking forward to your results. I have a softail stage 3 107 to 114. 11-1 SE-498 cam S&S Super Street 2-1 with Cat & SE Pro tuner.  It made 116/116.  Since then I added Fueling oil tank breather & a larger Db reducer. Then won a free dyno pull. It pulled 118/122. It picked up some sound volume but is not loud.  Bike still seems to be on point in every way. Part of me hates to mess with it. Been happy with it for over 3 years and 37k but now am trying to get more. 

Had wanted a 139ci but all considered have decided against it. Am & have considered a 128ci build. Really nice CP pistons, jugs, still its some coin.  But am also considered what I could do with existing jugs and Star's new F35A cam. Thinking having Wards port my intake. I'd gut the cat and swap to PV tuner.

George say's the F35A is designed to fit in a stock engine. It closes 10 degrees later than the 30 30 at 35 after bottom, has 572 lift, and is designed for 10.5 to 11.5-1.

We will perform leak down test & check crank runout. Just a hot rodder and ever learning hobbyist here. So this thread sparked me. If we decide to pull the heads and jugs to re ring freshen cylinders and make sure everything is square and seals good. Well then ridgidthumper goes and posts you could go 4.180 make it a 120ci and posts a link. $375 a piston isn't much. It would already come with fresh rings. Not much more to bore it. Only it says 12.0-1. 11.5-1 sounds safer and meets George's listing. Not sure I fully follow all these measurements and know all my options here. I'd be the assistant anyway but would be interested in what you all might suggest.

"He (Bryce) advised on using a .040" head gasket to allow for greater piston to head clearance and trapping more air in to the chamber etc."  I thought that was interesting.  George thinks deep.

Yes, theres definitely plenty of options out there for big bore M8 builds...

The comment Bryce made about the .040" HG in my application of the Star 30-30 was assuming I have a zero deck height. If I had .004" below deck height, the ideal HG thickness might be something different...  0.036" maybe, which Cometic actually make.

[Adam76]

I would not go above .038". But Star knows

Thanks, yes I thought Bryce would know better than anyone.

Now that my build is sorted, what 2-1 exhaust is best for the M8 softails??

* S&S super street seems very popular.
* Supertrapp Fatshot?
* Bassani Road Rage II / III with quiet baffle?

I've seen a lot about how exhaust sensitive these builds can be and don't want to get this far and stuff it up with a poor exhaust choice. 

[Adam76]

Well it sounds like it's coming together nicely. You won't be sorry that you took care of the details before diving in.

Thanks kd,

The last part of the puzzle is the exhaust....

The M8 softails are very exhaust sensitive, and I don't want to mess up my build with a poor exhaust choice.

What would you say are the best 2-1 exhaust systems for my application?

Thanks