Engine problems after 95" build part II - help needed

[kd]

Does it scavenge specs from a cam index for duration and overlap etc also (like the BigBoyz calculator) or does it just use the intake close spec?

[Ohio HD]

It uses intake closing.

I doubt that BB uses all of the specs. It gives the same answer if you pick a cam, or just type in a closing value.

[Adam76]

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

Thanks Ohio. Appreciate the calculations -- looks like it will bring me to a much safer compression.   

[kd]

It uses intake closing.

I doubt that BB uses all of the specs. It gives the same answer if you pick a cam, or just type in a closing value.

I was wondering if the other specs were part of the calc for the corrected compression at say 2000 rpm.  I guess it's not necessary and probably best if everyone is on the same page.

[Ohio HD]

I was wondering if the other specs were part of the for the corrected calc at 2000.  I guess it's not necessary and probably best if everyone is on the same page.

What's at 2,000?  Feet?

[kd]

Fixed it (I think)  .... always read the post before you push send.  It amazes me how much a sentence can change if it gets away on you.

[Ohio HD]

Well, when you get to any readings with the motor running, that's dynamic compression, and not cold cranking compression. It would take a lot of data to calculate dynamic compression. I'm not sure that I've ever seen that calculated.

[kd]

That was kind of where I was going.  I have seen where 2000 rpm has been used as where engine pulse is low and the CCR or DCR will react to valve closing, overlap etc. as rpm increases.  There are so many other influences it would be hard to track as a calculation. I hadn't noticed the cylinder growth in that calculator you used before.  I thought you shared it here once and I went to look in my calculator file for it.  I seem to remember you working up the cam list.  It says file not found now so I can't be sure. At any rate, because that calculator went the extra mile with cylinder expansion consideration, and the cam was entered with only the intake closing, I was curious. 

Adam, sorry for the hijack.   

[Don D]

The calculator works on some assumptions the most likely to be wrong is intake close. How many degrees is it from seat to .053" lift? A group of mathematic calculations by formulas is taken as gospel. How does a 9.3:1 CVO110 crank 225 with a 30° intake close? They do and that is proper according to the SM. They left the factory that way. Calculates out at 9.3 static 8.2 compression, corrected for intake close, and 183ccp. How is the actual 220+? We have elevated calculated CCP based on these spreadsheets as the defacto standard. Worse than that there are some that take the defacto rules as hard fast lines in the sand even in the planning stages. If this was my bike I would put a .040 head gasket on it and move on. Even then there is overhead considering the available octane.

[Ohio HD]

We all can agree that the calculation of corrected compression is based on the closing value listed for the cam. We can also agree that is not the actual closing as mention, some cams are actually closing at the value and then how ever many degrees the lift listed works out to be. Lifts being @0.053", 0.020". or 0.050" lift. The corrected compression calculation is an estimate.

The one fact that must be looked at is the statement made by the professional person that designed the cams, Wes Brown. He states that he wants to see the cams at 10:1 static compression.

The one thing we can be sure of is calculating static compression. As long as the data presented is real, It's merely the swept volume from BDC to TDC. The ratio between them.

With what we've been told the compression should come out at 10.1:1, using an 0.030" HG. Using an 0.040" HG the compression calculates as 9.9:1. In either case he should be fine. A consideration is that the larger the squish, the likelihood of detonation increases.

What would have been the best way to get there would have been flat top pistons, 0.030" HG, and set the heads at 80cc. He would have 9.9:1, right where Wes wants them.

[Adam76]

The one fact that must be looked at is the statement made by the professional person that designed the cams, Wes Brown. He states that he wants to see the cams at 10:1 static compression.

With what we've been told the compression should come out at 10.1:1, using an 0.030" HG. Using an 0.040" HG the compression calculates as 9.9:1. In either case he should be fine. A consideration is that the larger the squish, the likelihood of detonation increases.

What would have been the best way to get there would have been flat top pistons, 0.030" HG, and set the heads at 80cc. He would have 9.9:1, right where Wes wants them.

Thanks Ohio, yes Wes did state he likes them at 10.1 static compression....  Flat top pistons would have been a good way to.... unfortunately I started out with heads that were already 83cc.
And I  didn't choose the pistons for the build, they were chosen by the engine builder.

[kd]

Ohio, that's a great sensible train of thought.  You are right that the ratio of concern when having a conversation about compression for the cams is Static compression.   The guy that designed the cams says he prefers the 10:1 ratio then that's gospel.  The rest is just noise.  KISS as they say.  It appears Adam will be one point either side of the optimum and you can't expect much better.  Especially when trying to use the components in hand instead of starting from scratch.  I personally think it is working out well and would be tempted to use the .030 gasket to mitigate any risk of detonation.  But that's me and it doesn't matter.

[Don D]

It is impossible to back into hitting an exact compression number without machine work, get real. KB offers a 1cc piston that would have been equally deficient from achieving the exact designated static number. Now you can mill heads or mill pistons choose your poison. This is a custom motor build with some close tolerances being asked for and up to this point the deck height hasn't even been considered. Adam you are the builder, the man in charge. In all these pages of internet traffic there is some very good advice and solutions that have been presented. It is your turn to make it happen.

[ziggy24]

I have the bottom end back in the frame all bolted up and ready for the top end. Just waiting on some .040" head gaskets (Thanks Don) because with the .030" and the piston's dome volume of 6.7 has pushed my actual corrected compression to 9.8 and my ccp to 213.
With the .040" HG I'm at 9.64 corrected and 208 ccp -- still not sure that's going to be ok especially with the bike being carbed not EFI. It will be getting dyno tuned though and it has DTT ignition module.

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

Thanks


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This works well:

Ring Compressor

[koko3052]

Another method is to insert the pistons into the cyls on the bench,then slide the whole assembly onto the case. Pick your poison.

[Adam76]

Another method is to insert the pistons into the cyls on the bench,then slide the whole assembly onto the case. Pick your poison.

If they weren't KB pistons with Spiral locks for the wrist pin, I'd be doing that.  I find them tricky to work with. 

[Adam76]

This is just not my day...

I got the front cylinder over the piston quite easily (this is not my first top end rebuild) and then went to do the rear cyl and it just didn't want to go on and seemed offset.

Then I looked at the piston and it was not square in the case bore - not even close? The crank is good and only has 2 thou.

Do I have the pistons back to front??? The instructions that came with the KBs are not at all helpful.

Both pistons have the --> with the word FWD on them, so I assumed facing the front of the bike. But the thrust face is toward the rear, right?

This bike is cursed.


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[kd]

Simple stuff first.  Is there cutouts on the skirt for where the pistons meet?  The cutouts go to each other at the center of the cases (intake side).  The valve cutouts are usually different with the large radius to intake.  (That does look like an intake valve pocket,)  Is the piston over to the left side on the pin?   Were the pins (or at least the rear pin) a tight fit?

[Adam76]

Simple stuff first.  Is there cutouts on the skirt for where the pistons meet?  The cutouts go to each other at the center of the cases.  The valve cutouts are usually different with the large radius to intake.

Thanks kd, so what youre saying is the the arrows on the tops of the pistons should face backwards? Or face toward each other?

They look symmetrical to me.

Thanks

[kd]

Adam, I added to that post as you were typing.  I am not referring to the arrows.  I mean the physical characteristics of the pistons. I read my initial post and expanded on it in an edit.

[Ohio HD]

Take a photo of the entire top of the piston.

[Adam76]

Is the piston over to the left side on the pin?  Were the pins (or at least the rear pin) a tight fit?

The photo I took the piston was sitting in the middle / centre of the wrist pin. I can move it  the left and right, but even all the way right it doesn't line up with the bore.

The skirts on each side of the piston seem identical - and the intake and exhaust valve reliefs also look identical...

Thanks

[Adam76]

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[Ohio HD]

Pistons are in the wrong hole. There is a front and rear. And I think KB forged pistons have an offset pin if I remember correctly. Read the instructions that came with the pistons closely.

[Adam76]

Pistons are in the wrong hole. There is a front and rear. And I think KB forged pistons have an offset pin if I remember correctly. Read the instructions that came with the pistons closely.

Thanks, will do.