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Discussion Starter · #1 ·
I got into a conversation one afternoon with Mickey Foster while were were stealing coffee from Capital City Harley.

I mentioned that most engine-building companies build at least one engine style at about 120 inches. In fact, the rumored JIMS engine that Harley might/will offer is about 122 inches.

Since Mickey worked for several decades as a mechanic for many motorcycle brands, I asked him if this size was 'magic bullet.' You know, the most reasonable power and torque you could offer without making major frame mods to your average Harley. Mickey had a differing opinion.

He mentioned that he saw major engine failures and flat out more maintenance on engines bigger in size. Even with bigger engine cases, most bearrings, wrist pins and connecting rods just cannot take long term stress. He even opined that this concept might be the driving force in 6-speed transmissions as a way to lower revs and increase engine life.

I thought about this. V-Rods make a lot of power, but in a smaller size with extra cooling features. I've seen failures and one frame that cracked on Biker Build-Off using exotic engines. Even in the 1970's Harley used what was then called an INA bearring in their lower end, which offered a forged cage.

I wonder if this is a dirty little secret for larger V-Twin engines with an overall Harley design.

That is, keep them cool (i.e., more oil pressure than a shovel), strengthen load-bearing points, offer less than 100 ft/lbs of torque and aim for 120 inches.

Does this make any sense to you?
 

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Discussion Starter · #3 ·
So would I. It might determine on just what engine mods I make in the future.

I do know that you consider "piston feet per second." That is, a bike with a four inch stroke (like a Harley) has a piston that travels 8-inches for one revolution. A bike with a two inch stroke has a piston that travels half that distance. This effects torque, the ability to twist.

I'm thinking that if you increase the load to such an extent that bearrings and temperature cannot be controlled as in a conventional engine then wear increases to unacceptable rates.

That being said, I'm thinking that if I increase my engine size, I might only go 113 to 115 inches. In fact, if pricing is good, I might only go with Harley's 103B and a sensible cam.

But I'm not an engine builder. My understanding of metallurgy is for knives, not engine steel. What I think might be logical might only be an urban legend. And it takes money to modify an engine.
 

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You can build a strong reliable engine. HD doesn't offer it from the factory for one reason, MONEY. They want you to come back later. HD should have increased the size of motor in their bike years ago and didn't and it wasn't because they couldn't do it. HD used to be known for the largest motor in a bike and then suddenly they are one of the smallest.
 

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I look at it like a car engine. You can make some mild mods and still have pretty good engine life, but you reach a point that there is a lot of stress happening which says something evil will happen sooner or later. How much a Twin Cam crank, connecting rod or case will take would be interesting to know. Even if we do know how much the parts will take it still doesn't say how long they can with stand it. I'm sure that it is a safe bet to say, the more you beat it the shorter its life span will be. If the combination will rev to 6k+ rpm and a throttle jockey likes to hit 6,200 rpm on a frequent basis I have to bet sooner or later something expensive will break. Another way to look at it is if you can afford to build it you should be able to afford to fix it when it blows. I've seen race car engine with top notch parts scatter in short order because of a flaw in the metal that was missed. My brother had a near failure twice with the 540" BBC blower engine he runs in his Top Dragster which turns a close to 8k rpm. The 1st close call was when it was pulled down to freshen it up, he noticed a hair line crack down the connecting rod beam. The manufacturer gave him a new set of rods because they had a metal issue that caused this crack. The 2nd close call was this year when a push rod guide plate broke and caused the rocker arm to shift and trash the top of a valve stem and wreck a titanium retainer. What surprises me is some folks are putting together some potent builds yet I never hear anyone talk about magnafluxing (Spelling) parts such as cranks and rods, its like some folks assume the parts will handle the extra stress. Cams are a good subject, some of these more aggresive cams just beat the tar out of a valve train. A spring will only take it so long before it says uncle, that was one good tip I picked up from a old car engine builder. I had a cam grind picked out for my brothers engine when the guy said, sure it will make great power, but why beat the springs. He suggested a cam that made just as much power yet the spring life is awsome.
 

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Bottom Line: With more Power and more Cubic inches you lose reliability.
Now how much reliability is determined by what parts you put in the motor. It can still be a very reliable motor, just not the same as a stock motor.
Larger pistons and longer stroke all contribute to the stress on the engine parts and bearing for the reasons you said Tourist, more piston speed and more mass accelerating and decelerating in the motor at higher speeds.
I notice Fatb0y went with a Timken (notice spelling Fatb0y) bearing conversion which is a good idea on any larger motor upgrade.
I think is is possible to build a 103" or 107" motor with good reliability using the proper combination of parts but riding style may also contribute to how long a motor lasts.
A big inch motor that is reved to 6k rpm all the time will never last as long as one that is used on a touring bike that hardly ever sees anything over 4k rpm, but reving this high all the time may have very little affect on a stock 88" motor. Also lugging a big inch motor, which is a bigger problem than high revs, can destroy the bottom end of a big motor much faster than on a stock motor just because the forces are so much greater.
I would not fear going big if you do it right and treat it right.
 

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I do all sizes of custom engines, maybe redo would be more accurate when it comes to the biggest of them.
The real problem is room, when it comes to bores over 4" the cylinders are getting so thin that they lose stability.
The problem being that all custom engines must fit in the 1936 lower motormounts.
Another major concern is being stuck with 45 degree cylinders.
The engines over 4" bore are at a major mechanical disavantage.
The INA rod bearing introduced in 1973 is the result of manufacturing errors due to worn equipment at HD. This bearing with 17 rollers instead of the previous 18 per row has the rollers tapered toward the ends about .00015". This allowed the rods to rock slightly to compensate for misalignment in the crankcases without pinching the bearings into the crankpin. This bearing is easily identified by the 3 piece aluminum cage.
 

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There are lots of compromises made when buildin a high performance, big bore version of our beloved v-twin engine, especially when we need to shoehorn it into the same space that its smaller brother was. As bores get bigger and stroke gets longer we find that the pistons tend to want to meet atthe bottom. The compromise? Cut the skirts to gain clearance. It works, but it doesn't do much for piston stability. This can only have an adverse effect on durability and longevity. We take an OE motor and push the power way beond the design parameters and expect it to survive. Amazingly, they usually do. We may have to upgrade the TC-88 left side bearings to improve durability but mostly they take what we throw at them. We usually find thaht we have to upgrade clutches and drive systems to keep up. Double the horsepower on a small block Chevy and you may find that you need to go to a 4-bolt main, with a forged crank and rods to keep it together. I think that we are doing pretty well in our little world......Bill
 

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Yep... and you reach a point of diminishing returns fairly quickly. I personally think 4" bore is plenty. Stock - unbored - cases are better than a lot of what we're seeing now and 98" -- 3 15/16 X 4 -- is as close to square as you can get -- a good thing. My 98" is smoother than my 88" was, as well as a 95 I've ridden.

If you just gotta bore - 107 is the way to go, as there's a lot of "good" in an inherently smoother, oversquare engine.

But -- given the cost to go beyond 98", I would buy a second bike. Come rebuild time, if options are as they are now and you have to go into the cases anyway -- 107 makes sense.

Something to keep in mind is that for all the work and $$ we throw at these babies - a 600 will probably whack all but a few hot rod Harleys, and a litre bike will get the rest.

Just last week I looked at a new S2R Ducati Monster. Air-cooled, 2-valve. 95 HP, 70-something TQ and 399 pounds dry. Cost $9K and change. I figure I've got $5 in my motor and were I to do it again - I think I'd buy a bagger, do a simple Andrews 26 BB, and then pop for a Duc. More cost efficient and a lot more fun.

That said - plenty just "got to have it" and for them that have the bug, that beefy JIMS 120 looks mighty good. JMHO.
 

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FXDRYDR said:
Just last week I looked at a new S2R Ducati Monster. Air-cooled, 2-valve. 95 HP, 70-something TQ and 399 pounds dry. Cost $9K and change. I figure I've got $5 in my motor and were I to do it again - I think I'd buy a bagger, do a simple Andrews 26 BB, and then pop for a Duc. More cost efficient and a lot more fun.
HAHAHA, I'm with ya. That's how I ended up with my Springer and my Buell XB9R. BTW, My stock 9R ran rings around the Ducs on the track.
 

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Sprung said:
HAHAHA, I'm with ya. That's how I ended up with my Springer and my Buell XB9R. BTW, My stock 9R ran rings around the Ducs on the track.
Cool!! Where ya the Ducs you were spanking the 1000s? If so, was it handling, outright power - or both? The S2 - 1000 is what I saw, and it's "old tech" in the sense that the newer, S4 Monsters are water cooled, have 130+ HP and about the same torque curve. They cost around $15K. I'm a "muscle bike" kind of guy and figured that if my scooter weighs 650 or so and ran 11.9 -- then a bike with close to the same HP and 250 lbs less weight ought to be a whole lot more fun.

Of course, I really like the 130+ HP model -- but again, for cost efficiency I love the idea of 95 HP in 400 lbs for $9K!! Thought about the Buells too and they're a great machine. Didn't think they had the power to weight of the S2 1000 Duc.

Frankly, had never even considered a Duc before last weekend. Just happened to go by a dealership, and so stopped to check them out. Was with a friend shopping for a 1200 Sportster. I was very impressed with what I saw of the Ducati. Guy offered to let me take it out, but it was too damn cold!!
 

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FXDRYDR said:
Cool!! Where ya the Ducs you were spanking the 1000s? If so, was it handling, outright power - or both? The S2 - 1000 is what I saw, and it's "old tech" in the sense that the newer, S4 Monsters are water cooled, have 130+ HP and about the same torque curve. They cost around $15K. I'm a "muscle bike" kind of guy and figured that if my scooter weighs 650 or so and ran 11.9 -- then a bike with close to the same HP and 250 lbs less weight ought to be a whole lot more fun.

Of course, I really like the 130+ HP model -- but again, for cost efficiency I love the idea of 95 HP in 400 lbs for $9K!! Thought about the Buells too and they're a great machine. Didn't think they had the power to weight of the S2 1000 Duc.

Frankly, had never even considered a Duc before last weekend. Just happened to go by a dealership, and so stopped to check them out. Was with a friend shopping for a 1200 Sportster. I was very impressed with what I saw of the Ducati. Guy offered to let me take it out, but it was too damn cold!!

It was handling and skills (IMHO). I love the Ducs, but I have never had so much fun as a Buell XB on the track, with the suspension accurately dialed in. Last session, I wore my knee puck down to the leathers and ground down about 3/8 of an inch on the peg feelers (and the Xb has over 45 degrees of lean angle before they touch). What a rush! That said, I'd love to have a Duc AND keep my Buell. I've had two of the XB's and they have been bullet proof, dead reliable, and easy to maintain. That means a lot to me. You would enjoy either bike, but keep a cruiser for when you realise you just can't control the urge to fly and you need to settle down a little.
 

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The Tourist said:
That is, keep them cool (i.e., more oil pressure than a shovel), strengthen load-bearing points, offer less than 100 ft/lbs of torque and aim for 120 inches.

Does this make any sense to you?
Ya might be onto something.... except why do ya need a 120 inch engine to make 100 ft. lbs. of torque? You can get that out of an 80 incher without major mods and it will cost you a lot less. You just need the right combination of parts and some good dyno tuning. Keeping it closer to stock displacement will make for a more reliable machine. Bigger is not alway better when it comes to engines. :)
 

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Discussion Starter · #15 ·
Thanks for the info guys, it's a lot to think about.

I'm more of the kind of guy who believes "there's no substitute for cubic inches."

But having said that, I'd go with a more mild set of build components. You know, lower compression pistons, rounder cams, mid-size valves, etc.

I did not know about the age of the design for HD stock motor mounts, and that's an issue all by itself.

I could get a perfect TP or JIMS engine running like a clock and then crackthe mounts.

Right after fire was invented,weused to see a lot of cracked rear Sportster motor mounts. In fact, Rickie Ratchet of the old Decker's Harley guessed that most of the Sportster mounts of that era were cracked. I think the years was either 72 or 73, but we actually got extra struts we had to weld into the frames of Sportster's to buttress the frames.

Of course, just about the time I get things clear in my head, I see a CVO Fat-Boy...
 

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The Tourist said:
Thanks for the info guys, it's a lot to think about.

I'm more of the kind of guy who believes "there's no substitute for cubic inches."
I know what ya mean! :D I have that same belief when it comes to V8s. I used to race an Ford Grand Torino Elite with a 460 bored out to just under 500 inches. That car weighed about 3800 lbs and I could lift the front wheels a few inches off the ground. I've found that a bike is more reliable if you don't have an excessive compression ratio or displacement. I ride tens of thousands of miles a year, so reliability is the number one priority... after safety, of course. Of course, boring it isn't as bad as stroking it. I used to stroke a lot of old Shovels and they beat the heck out of the bottom end.
 

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Discussion Starter · #17 ·
Based on what Mickey told me, backed up by the theme of the Hells Angels bikes of San Francisco I just saw on cable, I'm shooting for "big and bullet-proof."

My only concern is that if a 'mild tune' large Harley (or large case replica) stresses components like a 'wild tune,' am I gaining anything?

Just this week, a sharpening client told me he just put what he called a "Harley 4E" cam into his dresser and got better performance, no glitchy power spikes and better gas mileage. I asked him, also, about stress on the engine. He replied that his primary use of the bike was cruising at moderate speeds with his wife.

My 95-inch has a stock cam. And I'm leaning to 'more inches' not 'scalded dog' as a way of increased passing power. (I want the horses between 50 and 80 MPH, not high or low.)

You in-put is what I want.
 

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The Tourist said:
Based on what Mickey told me, backed up by the theme of the Hells Angels bikes of San Francisco I just saw on cable, I'm shooting for "big and bullet-proof."

My only concern is that if a 'mild tune' large Harley (or large case replica) stresses components like a 'wild tune,' am I gaining anything?

Just this week, a sharpening client told me he just put what he called a "Harley 4E" cam into his dresser and got better performance, no glitchy power spikes and better gas mileage. I asked him, also, about stress on the engine. He replied that his primary use of the bike was cruising at moderate speeds with his wife.

My 95-inch has a stock cam. And I'm leaning to 'more inches' not 'scalded dog' as a way of increased passing power. (I want the horses between 50 and 80 MPH, not high or low.)

You in-put is what I want.
For the best torque (not power... HP is basically a worthless number when talking about Harleys), your choice of cam and exhaust will have a lot more effect than engine size. If you want stump pulling and awesome passing torque without having to downshift, then you need a low duration, higher lift cam and a good 2-1 tuned exhaust. Just making those changes will have a HUGE influence on how your bike runs on the street. I have left some 100+ inch engines in the dust with my 80 incher on more than one occasion. It's all about how you match the components, not how big the engine is. These aren't V8s. Big inch engines are more for bragging than for a good reliablilty/performance balance. That's why so many RUBs are buying them... so they can sit around the yuppie bar and yap about it. :(- Those guys don't usually ride tens of thousands of miles every year like the 81 guys do. Many are lucky to make one run a year over 500 miles. Personally, I prefer to build for reliability rating higher than performance, but a good combination of the two is easily made with proper planning.-2$en#e-

A word of advice... don't believe everything you see on television. :)
 

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Chico, you have 95" but do you have anything else done yet like head work or stage 1? I suggest you have Sean at Cap City do your heads and build you an engine. He did my heads(sounds funny, doesn't it?) and in fact he is the only one who has done any engine work on my TC. He builds great engines and will build it for your style.
 
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