Engine problems after 95" build part II - help needed

[Ohio HD]

Also what is the piston deck height?

[Adam76]

What are the piston CC's?

Domes are 6.7cc KB + 40 pistons

[Adam76]

Also what is the piston deck height?

Haven't assembled yet to measure, but I'm basing it on .005 and hoping it's not less...

[Ohio HD]

Change the pistons to 3.5cc in your calculations.

I'm sure that the piston manufacturer can tell you how much to machine from the dome.

[kd]

That's a good idea.  You will get to see the relationship between static and corrected.  Static is the calculated difference between the swept column of air in the cylinder and the head CC (including gasket).  Corrected is the actual compression you should find and is usually as a result of the intake valve timing on relation to BDC.   

BTW I (and others) have used base gasket thickness to dial in deck height.  My 120 was out of the hole so I added to the base gaskets to get 0 deck.  For you, it would lower your compression but also open up the squish.  Having a tight squish around .030 is optimum in controlling detonation.  You can end up chasing your tail.  On the other hand, the CR575 is at 35* ABDC which is not as bad as some and the stated best compression is in that 10.5 zone so it should run great.   

[Adam76]

the CR575 is at 35* ABDC which is not as bad as some and the stated best compression is in that 10.5 zone so it should run great.   

So your basically saying 10.3 static and 9.65 corrected with 205ccp should be OK ?

Thanks

[kd]

I think it would be a bear off idle and may hold up to about 5000 rpm from what I have seen and notice in a few builds.  I followed the CR575 a bit when I saw the instant torque off idle.  I have come to believe it needs the compression Wes at Cycle Rama recommends.  Any downsides in your build (if any) are probably best discussed with him. I'm sure he will be able to tell you what to expect.

[wfolarry]

A lot of KB pistons have a hollow dome. Measure the thickness before you do any cutting.

[Don D]

This is Australia, they have 95-98 RON octane available, the bike is carbureted, and the dome is .341" in the center, no under dome milling. It would take .062" cut to get to 3cc. Not a recommendation just the stats.

[SP33DY]

Any tips / tricks on slipping the cylinders down over the pistons during assembly? What's the best method? Ring compressor tool?

These adjustable ring compressors work the best for me. They are made for inserting pistons from the top, but by cutting about 3/8" of material from the gap to make it possible to remove them past the con rod and studs, they work great on a Harley. I set the diameter by installing it upside down on the piston and rings assembly and making sure it slides up the skirt with just a little bit of drag. Then slide it off the piston, flip the tool over and slide back on. Lock the flywheel from turning and slide the cylinder on. It works well with even the skinniest rings out there.

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[SP33DY]

Installing cylinder

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[Don D]

  
Nice tool for sure, good idea

[Adam76]

This is Australia, they have 95-98 RON octane available, the bike is carbureted, and the dome is .341" in the center, no under dome milling. It would take .062" cut to get to 3cc. Not a recommendation just the stats.

Looks like with the shape of the dome and the valve reliefs, it may be tricky to mill the domes down? 

Even if I do mill them a small amount -- I'm probably still going to need to use a .040" HG.


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[Don D]

Cut to the dimension I provided. Flat top cut.
If you work with a shop like Hood Motor Service, I provided information, this is something Mark will be very comfortable with. If there are no high performance shops near by I would ship then. I cut them on a back plate on the lathe with a draw bar or set up a piston vise and use the mill. Key is holding them right so they are not damaged. Not suggesting sending them back here, freight is too costly

[kd]

Adam, have you determined that you in fact have too much compression for the CR575 cams that you are using?  Did you consider calling (or emailing) Wes at Cycle Rama with your specs for advice yet?  If you email him first with your present specs he will have time to consider any advice he may have.

[harpwrench]

I'd just suck it up and buy the S&S 570's that you already know you want

[jsachs1]

What are the piston CC's?

Domes are 6.7cc KB + 40 pistons

I've removed .030" off those piston domes, and wound up with 5.2 cc domes.
John

[Adam76]

Adam, have you determined that you in fact have too much compression for the CR575 cams that you are using?  Did you consider calling (or emailing) Wes at Cycle Rama with your specs for advice yet?  If you email him first with your present specs he will have time to consider any advice he may have.

This is the reply I got from Wes.


Cycle-Rama Wes Brown
Sun, Jan 9, 6:11 AM (1 day ago)
to me

I dont like running them over 10.0
I have a lot of customers that do run them at 10.5
Tune must be spot on
You can get a set of. 051 head gaskets cometic makes them.
I have used them before with no problems

[Adam76]

What are the piston CC's?

Domes are 6.7cc KB + 40 pistons

I've removed .030" off those piston domes, and wound up with 5.2 cc domes.
John

Thanks John, I'm looking at removing .055" as per Don's recommendation... Would you agree that that is about the right amount to mill to end up with 3cc domes?

Thanks.

[Adam76]

Cut to the dimension I provided. Flat top cut.
If you work with a shop like Hood Motor Service, I provided information, this is something Mark will be very comfortable with. If there are no high performance shops near by I would ship then. I cut them on a back plate on the lathe with a draw bar or set up a piston vise and use the mill. Key is holding them right so they are not damaged. Not suggesting sending them back here, freight is too costly

Thanks, will go and see a few machine shops today and see if it can be done.
I will also contact Hoods Motor Service.

[kd]

   Glad to hear you seem to have a concrete plan based on facts now Adam.  Looking forward to seeing success.

[kd]

What are the piston CC's?

Domes are 6.7cc KB + 40 pistons

I've removed .030" off those piston domes, and wound up with 5.2 cc domes.
John

Thanks John, I'm looking at removing .055" as per Don's recommendation... Would you agree that that is about the right amount to mill to end up with 3cc domes?

Thanks.

John will likely answer but doing the math, I see 1.5 cc per the .030" removed 5.2 cc domes John states he got.  That's .5 cc per each .010" so .055 will be 3 cc in my book.  If you have 6.7 cc domes you'll end up at 3.7 cc.   

Now, looking at the pic of your pistons, as the cut gets deeper you will be removing more material as the depth milled takes you down deeper into the valve reliefs.   That, and the ballpark numbers being used, "may" bring you closer to having 3 cc equivalent remaining.  At any rate, it should be real close to your goal if you are after that 10:1 .

[Ohio HD]

Yep, and you can use an 0.030" head gasket of the pistons are down 0.005" as speculated.


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[kd]

Nice.  Ohio, I like that calculator.  It has cylinder growth potential for heat in the tables.  Is that something you put together?

[Ohio HD]

It's partially mine. Someone else created the bare bones calculations. I added a few things, and spruced it up a bit.