Head porting and balancing
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HDF Community Team
Joined: Dec 2005
Posts: 5,403
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From: NC USA
When I had my evo stroked, the engine builder told me before he started that the big end of each rod would be out of round. They were by a few thousandths of an inch each, so he honed them round and rebuilt the engine with over-size rollers. Not the same as being 'bent', but a known long standing problem with Harley rods. I haven't heard if TCs suffer.
Harley is not alone in using offset shaped combustion chambers. It does not result in the firing force on one side of the piston. The combustion space is like a balloon, with equal pressure all around and pressing across the whole piston surface at the same time. Think of sidevalve engines - they have an extreme form of offset, but have survived without rod problems caused by the offset.
Harley is not alone in using offset shaped combustion chambers. It does not result in the firing force on one side of the piston. The combustion space is like a balloon, with equal pressure all around and pressing across the whole piston surface at the same time. Think of sidevalve engines - they have an extreme form of offset, but have survived without rod problems caused by the offset.
Granted, it was just to prove a point to myself and I wouldn't do to someone else's engine....
Elite HDF Member
Joined: Sep 2007
Posts: 4,468
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From: Bluffton, South Carolina
OK. I had NO intention of doing it to mine, just wanted some opinions.
I had a feeling it was not much advantage without a LOT of other mods. And I agree in theory - the more you can "move" the more it will do. However, when you're sucking in explosive mixture (gas/air) with the intention of making the "pump" do the work, rather than the pump being the result of another power source, that changes the formula. I've read a little, but enough to realize the angle and velocity of the mixture intake is a big factor pertaining to what's actually (supposed to be) happening.....
hmmmm ... maybe I forgot my medication this morning
I had a feeling it was not much advantage without a LOT of other mods. And I agree in theory - the more you can "move" the more it will do. However, when you're sucking in explosive mixture (gas/air) with the intention of making the "pump" do the work, rather than the pump being the result of another power source, that changes the formula. I've read a little, but enough to realize the angle and velocity of the mixture intake is a big factor pertaining to what's actually (supposed to be) happening.....
hmmmm ... maybe I forgot my medication this morning
Twisted rods: as any competent engine builder power can be obtained by "blueprinting" an engine. The closer you get all dimensions, weights, capacities to being equal the better and longer an engine will perform. The experienced engine builder knows which dimensions, etc. should be at the minimums and which should be larger. Most parts come from the factory close but some are defenitely off. This helps explain why two bikes that are "the same" , one will out perform the other. The bike that runs better has all the parts from the factory that are closer to specs than the other.
Now with all that being said for the street you and your engine builder must determine what suits your needs and pocketbook. As we've always said" speed costs how fast do you want to go??"
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HDF Community Team
Joined: Dec 2005
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From: NC USA
Your pump is being turned by another source in essence. The reciprocating action of the rods and pistons are turning the engine. The more air that you get to go through at any give RPM will bring more fuel with it, resulting in more power. You can not get more power without burning efficently more fuel unless you had a significant restriction and were wasting fuel.
Twisted rods: as any competent engine builder power can be obtained by "blueprinting" an engine. The closer you get all dimensions, weights, capacities to being equal the better and longer an engine will perform. The experienced engine builder knows which dimensions, etc. should be at the minimums and which should be larger. Most parts come from the factory close but some are defenitely off. This helps explain why two bikes that are "the same" , one will out perform the other. The bike that runs better has all the parts from the factory that are closer to specs than the other.
Now with all that being said for the street you and your engine builder must determine what suits your needs and pocketbook. As we've always said" speed costs how fast do you want to go??"
Twisted rods: as any competent engine builder power can be obtained by "blueprinting" an engine. The closer you get all dimensions, weights, capacities to being equal the better and longer an engine will perform. The experienced engine builder knows which dimensions, etc. should be at the minimums and which should be larger. Most parts come from the factory close but some are defenitely off. This helps explain why two bikes that are "the same" , one will out perform the other. The bike that runs better has all the parts from the factory that are closer to specs than the other.
Now with all that being said for the street you and your engine builder must determine what suits your needs and pocketbook. As we've always said" speed costs how fast do you want to go??"
And I totally agree with those facts as to why engines/bikes each have their own personalities.
I don't wanna go fast, so much as I want to go long. From the crankpin up, I AM my engine builder...
Last edited by t150vej; Apr 23, 2009 at 01:33 PM.
Tourer
Joined: Feb 2008
Posts: 383
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From: Richmond BC.
Quite often I have found bent rods, they are easy to check with the barrels off and bottom end together. Get yourself a checking pin from Jims, S&S and others. It's just a longer piston pin that extends over top of the cases when installed through the small end of the connecting rod, there are different sizes depending on your motor so make sure you get the right one. You then have 2 pieces of thin paper between the rod and the cases pull them at the same time to make sure the clearance is the same. Jims also has a straightening tool. You can also tell by the wear on the thrust side of the piston. If the rods are bent you will get extra noise and could hammer the wrist pin clip out of the piston.
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HDF Community Team
Joined: Dec 2005
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From: NC USA
Well, there ya go... you just told why I feel "balancing" an HD engine is a joke, unless you're racing, I'll stay off my soapbox about that....
And I totally agree with those facts as to why engines/bikes each have their own personalities.
I don't wanna go fast, so much as I want to go long. From the crankpin up, I AM my engine builder...
And I totally agree with those facts as to why engines/bikes each have their own personalities.
I don't wanna go fast, so much as I want to go long. From the crankpin up, I AM my engine builder...
Just wanted to clarify something. Balancing is a necessary part of the "process" when starting from scratch or with stroker flywheels, adding big bore stuff or changing to exotic rods etc. What I meant was that for the typical rebuild, it's probably not worth the time/expense in significantly reducing engine vibration unless you want to do it yourself for the piece of mind.
Tourer
Joined: Feb 2008
Posts: 383
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From: Richmond BC.
I recently rebuilt a 110 s&s motor and decided to have it ballanced as I have done with most motors I have built over the last 30 years the difference was like night and day especially at normal cruising speeds. I guess if your running a rubber mounted motor or a B motor with counter ballancers then it won't be as big of a deal but with a solid mounted engine and no counter ballancer being in ballance makes a huge difference.
Club Member
Joined: Jun 2007
Posts: 45,429
Likes: 2,898
From: Bedford UK
I had my original 1990 motor stroked and tuned by a UK builder who did an excellent job balancing it. It really was remarkably smooth and sweet running. I just wish my S&S 107 was as good!
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