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Author Topic: Team Go Dog, Go! Modified Partial Streamliners  (Read 519243 times)
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wobblywalrus
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« Reply #120 on: April 07, 2010, 12:51:45 AM »

The engine speeds for seven of ten Bonneville runs are calculated from the data we recorded and the time slips.  This is shown on the sheet.  I usually try to run at 7,500 rpm.  This is my target RPM and I adjust the gearing to get as close as possible.  This rpm give me nice fast runs and it does not put a heavy strain on the engine.  In a pinch, and only if bringing home a record will depend on it, I will put on a one tooth bigger rear sprocket and go for broke.  This will get me a few mph but it is not good for the engine.  It will be just over 8,000 rpm and right near red line.

The rpm data helps me to make decisions about the new build.  One of the original 790 cc pistons is shown in the photo.  There is a small crack in the skirt and a chip is missing from the corner.  This is a cast piston.  It is showing damage from use and it has not been over 7,500 rpm.  It would probably fail at 8,000 rpm.  Unfortunately, I bought another set of larger cast pistons for the new build.  They will not be used.

Will forged racing pistons, which are stronger, be the answer?  Forged pistons should be good for up to 4000 feet per minute average piston speed in sustained use and work at up to 5,000 feet per minute in intermittent bursts.  The average piston speed formula is:  V = S x R /6.  V = average piston speed in feet per minute, S = engine stroke in inches, and R = engine speed in revolutions per minute.

The Bonneville's connecting rods will break at about 9,000 rpm, so the rev limiter is set at 8,300 rpm.  The engine cannot exceed this speed.  Using an 8,300 rpm engine speed and the 2.68 inch stroke:  V = 2.68 x 8,300 / 6 = 3,700 feet per minute.  This is well under 4,000 feet per minute.  Good quality forged pistons should be safe for this bike. 

 





* RPM for runs.jpg (71.49 KB, 442x336 - viewed 215 times.)

* Cracked piston.JPG (68.48 KB, 448x299 - viewed 240 times.)
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wobblywalrus
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« Reply #121 on: April 08, 2010, 09:45:21 PM »

The average piston speed formula tells me what I should do in terms of periodic piston inspection and replacement.  Cast pistons, as a rule of thumb, I consider reliable with little or no inspection at sustained speeds up to 75 percent of 4,000 feet per second maximum, with occasional bursts over that speed.  3,000 feet per second is 75% of the 4,000 feet per second maximum.  Periodic inspection and replacement is the rule for average speeds over 3,000 feet per second, and the frequency of inspection and replacement increases as piston speeds near 4,000 feet per second.   Let's say I continue to use these cast pistons.  They would be replaced every ten runs, based on the very tiny skirt crack that I saw, and I would continue to keep the rpm below 7,500.

Forged racing pistons follow the same rule for me, except I do not worry about them unless sustained average piston speeds are more than 75% of 5,000 feet per second, or 3,750 feet per second.  This corresponds to 8,400 rpm on the Triumph.

This rule of thumb has helped me quite a bit during my younger years when I did most of my tuning, and it worked good for me for this Triumph in land speed use.  It is a lot cheaper to replace parts before they break.
 

 
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wobblywalrus
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« Reply #122 on: April 10, 2010, 10:42:43 AM »

The engine part of this build diary appears to be a set of random events.  It follows a logical pattern, sort of.

High engine speeds (RPM) for sustained periods seem to be the main killer of naturally aspirated motors in LSR, based on what I learned before the engine tear down.  A history of engine rpm is needed to make decisions during the engine work.  I had tachometer data from only a few runs.  The tach info that I had was used to figure out tire slip/tachometer error factors.  These factors, along with the gearing data that I wrote down, and the speeds on the time slips, gives me the info to figure out a history of run rpm.

Next, I have a realistic discussion with myself about what I can, and want, to do with this bike.  It can never compete head to head against the modern water cooled Japanese fours.  They produce much more power than the Triumph and I can never get the power I need.  In addition, this engine work is costing me big money and using a lot of time.  In the interests of family finances and marital stability the engine must stay together for at least another five years.  This is the goal.  As much power as I can get and no tear down for five years.

The weak link in these engines is the cam chain.  Mine needed replacement after ten runs and I cannot find a high performance chain.  The history shows me that it took ten runs to wear out the chain at engine speeds up to 7,500 rpm.  High engine RPM and number of runs kills these chains, so I will continue to use 7,500 rpm as a target during my runs with the rev limiter set at 8,300 rpm.  Also, I will limit myself to ten runs down the salt in the next five years.

Now I have my upper rpm limit.  This is the first step in tuning.  I know that I need to get as much power and reliability as I can within that limit.   

 
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Geo
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« Reply #123 on: April 10, 2010, 12:29:59 PM »

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I have a realistic discussion with myself about what I can, and want, to do

Wobbly,

Thanks for having this conversation within earshot!  Love your reasoning.  Keep it up.

Geo
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« Reply #124 on: April 11, 2010, 03:25:31 AM »

wobbly
with a good seasoned block i would run those cast pistons.... especially on a slow rev'n NA motor.... look under the dome... I'm sure it is undercut and lighter around the pin area than the forged... the cast probably has less material under the dome and can dissipate the heat to the rings better than most mass forged slugs.... you can run a tighter clearance with them than a forging.... I would have to look at your cracked piston but i doubt it was due to piston speed... cast pistons spin to 13, 14 and even 15g all day long in those new sportbikes, so i have doubt.... we use power adders like NOS and turbos so we need a strong dome and ring lands so we use forged but on a NA motor like yours i would prefer cast
Kent
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wobblywalrus
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« Reply #125 on: April 11, 2010, 12:51:10 PM »

Kent, Triumph might have recognized a problem with those 790 cc pistons.  They went to much better cast pistons when they went to 865 cc.  Like you say, they should be OK for 7,500 rpm.  I have a set.  There were other reasons I used forged jobs.

About 40 years ago I was explaining to my father some hop up that I was going to do to my Matchless or 305 Honda Superhawk.  My father said something like "Look, someone smarter than you designed that thing from the top of the rocker cover to the bottom of the oil pan to handle the loads and stresses based on the power it has.  You are going to double some loads and you will be chasing problems from the rocker cover to the bottom of the pan."

About two years ago I did the math to figure out that the 790 cc pistons were over stressed and I would need to look at options.  The 790 cc engines were only used for a couple of years and there are no high strength pistons for that bore.  Stronger parts were available but they were all in big bore or stroker kits.  I looked at these setups using math and my experience with air cooled engines.  During all of this I remembered my father's words.

One option I looked at was reducing bore diameter, having custom pistons made, and doing other work to make a modified 750 cc engine.  This seems to be the best approach to making this motor into a heavily built LSR engine.  The use of a larger engine as a platform to build a smaller racing motor is something I always look at, and it is a minority viewpoint, for sure.   The task at hand is to build a nice street engine, and a racing motor is in the distant future.

Back before the recession I bought a new 865 cc cylinder block and a set of new 865 cc cast pistons.  They are much better quality.  A look at the piston side shows a nice radius where the 709 cc piston had a 90 degree cut.  A view of the piston bottom shows less sharp radii.  These larger pistons have fewer places with stress concentrations.  I expected to have no problems with running them at 7,500 rpm and I would take the cylinders off and inspect them if I ran over 8,000 rpm.

There are problems with these pistons.  They are only available in a 9.1 to 1 compression ratio.  I am installing a higher performance cams and the valves will be open for longer times.  Less air will stay in the cylinders at lower to mid rpm for combustion.  In effect, the cams will be lowering my compression ratio at the engine rpms I use on the street.  Another problem with the cast pistons is they have no gudgeon pin offset.  The piston, pin, and connecting rod all change direction at the same time at top and bottom dead center.  This puts a heavy instantaneous load on the rod big end bearing.  I was prepared to live with both of these problems.

South Bay Triumph recently developed high compression (10.5 to 1) pistons for an 865 cc engine.  They are forged Arias pistons with slightly offset pins.  The pistons and connecting rods reverse direction over a slightly longer period with these offset pins.  It reduces the instantaneous loads on the rod bearings.  This is a good thing for a LSR engine.  The pistons are also designed so there are much fewer sharp corners for stress concentration.  I ordered a set with teflon coating on the pins and pistons.  Now I will have no problems, that I know about, in the pistons and cylinders.   

 

 

I al  appeared to be the best sleeving th 


* Better Cast Piston 1.JPG (59.07 KB, 448x299 - viewed 195 times.)

* Better Cast Piston 2.JPG (61.58 KB, 448x299 - viewed 209 times.)

* Forged Piston.JPG (65.53 KB, 448x298 - viewed 194 times.)

* Three Stooges.JPG (80.65 KB, 448x299 - viewed 229 times.)
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wobblywalrus
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« Reply #126 on: April 13, 2010, 12:35:02 AM »

The old saying "its better to find the sabertooth tiger than it is for the tiger to find you" applies to this part of the build.  Finding all of these problems is not pleasant, but it is better than the alternative.  I hope that I find all of them.

It was a pleasant evening.  All chores were done and I slipped down into the basement for some quality time with the scoot.  It was time to pull the rods off of the crank and to put in some new bearing shells.  Easy enough, but then I noticed black stains on my hands.  They looked like that Arco Graphite oil that was popular years ago.  Serious swearing echoed from the basement walls.  Rick Vogelin, in his "The Step-by-Step Guide to Engine Blueprinting" says it best.  "Black carbon deposits around the big end of used connecting rods are warning signs that the overheated bearing was on the verge of spinning."  This is a problem I need to fix.  The increased loads from the new motor will spin the bearings, for sure.  New barrels cost $1,706, crankcases $3,861, rods $139 ea, etc.  I need to get this one fixed right the first time.  Fortunately I was warned ahead of time, and I have some advice.   


* Burned Oil.JPG (91.03 KB, 448x299 - viewed 205 times.)
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wobblywalrus
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« Reply #127 on: April 15, 2010, 12:52:43 AM »

The rod big end bearing is like the eleventh piglet on a ten tit sow.  It gets what the others leave.  In this case, the rod bearings are the last in line and they get the oil that does not go through the main bearings.  The rod journal holes will be chamfered to slightly increase oil flow into the rod bearings and to spread the oil out more evenly.  This will improve the bearing lubrication.

Only the rod bearing journal oil holes are chamfered.  The main bearings look fine and I do not want to increase flow through them.  I will put new inserts on the main bearings to minimize flow though them and to keep the oil pressure up.  This will assure that the rod bearings are getting their full share.

A chainsaw sharpening stone is used for the initial rough chamfering.  A grit impregnated rubber bit is used for the final polishing.  This larger opening will help to lubricate the rod bearings.  The rod bearing oil holes are enlarged in some extremely high performance uses, but this engine does not need that.


* Chainsaw and Rubber Stone.JPG (78.93 KB, 448x299 - viewed 205 times.)

* No Champher.JPG (61.83 KB, 448x299 - viewed 196 times.)

* Rough Champher.JPG (66.76 KB, 448x299 - viewed 205 times.)

* Smooth Champher.JPG (59.24 KB, 448x296 - viewed 214 times.)
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wobblywalrus
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« Reply #128 on: April 18, 2010, 12:35:20 AM »

The Triumph oiling system is completely different from the old Triumphs.  I study it and decide to chamfer all of the crankshaft oil holes.  Triumph make rod bearing shells in slightly different sizes.  They are coded with paint marks.  My original shells are red.  I order and will install white shells.  This will give me 0.0003 inches additional bearing clearance.  There will be increased oil flow through these looser bearings and the oil will carry away more heat.  South Bay Triumph recommended this fix.

The next step is expensive.  It is a set of Carillo top loading connecting rods.  These rods unbolt from the top and the rod bearings can be inspected and replaced without removing the engine from the frame.  Will my new heavier forged pistons increase rod bearing stresses enough to warrant the Carillos?  What about future changes, will they also increase rod bearing stresses?  It is time to do some figuring.

First, I need to determine the reciprocating mass.  This is the piston, rings, gudgeon pin, clips, and the upper portion of the connecting rod.  I weigh the pistons, rods, and the small end of a connecting rod. 


* Weighing Piston.JPG (67.54 KB, 448x299 - viewed 194 times.)

* Weighing Rod.JPG (72.73 KB, 448x299 - viewed 205 times.)

* Weighing Rod 2.JPG (74.57 KB, 448x299 - viewed 212 times.)
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wobblywalrus
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« Reply #129 on: April 21, 2010, 12:12:37 AM »

Five engine build alternatives will be examined.  The old 790 cc engine will be the baseline.  I have its history.  The second is the 865 cc engine with the better quality cast pistons.  Third is an 865 cc engine with forged pistons.  Hopefully it will be what I race this year.  An engine with a 994 cc big bore kit will be looked at.  I dream about this.  Maybe I will find buried treasure in the back yard.  Last, I will examine a 750 cc small bore high rpm engine, out of curiosity.

Three engine speeds will be used.  7,500 rpm is my current target speed.  The 8,400 rpm rev limiter speed will be looked at, too.  The engine should not blow up at this speed.  The last speed is 9,000 rpm.  This would be the redline for a future race engine.

Rod big end bearing loads will be figured for the point near top dead center where the rod and piston are subject to the highest inertial tensile loads.  Loads will also be figured for the big end bearing near bottom dead center where the rod is at its highest compression due to inertial loads.  I will also look at rod loads when the piston is applying maximum force due to combustion, if I can remember how to do it.

A long time ago I was 17 and I bought a new copy of the Fall 1970 "Motorcycle Sport Quarterly" by Petersen Publishing.  An article "Engine Science" by Phil Vincent is in there.  Most of the equations I use are in the article and a few are my own.

The piston is reciprocating mass.  It goes back and forth.  The crankshaft is rotating mass.  It spins.  The connecting rod is both.  The small end is reciprocating mass and the big end is rotating mass.  I use the old style method of hanging the rod and measuring the small end weight on a scale.  The small end is considered to be reciprocating mass along with the piston, rings, and pin.  The 750 cc and 994 cc piston masses are estimated using a ratio of bore areas.  These are approximations. 


* Page 1 Load Calcs.jpg (69.2 KB, 336x440 - viewed 233 times.)
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« Reply #130 on: April 21, 2010, 09:10:22 PM »

Wobbly,
Upon further consideration, I think you will realize that for the purposes of big-end bearing load calculations the entire connecting rod mass should be used.  After all, the "vertical" velocity and acceleration of the con-rod CG is essentially the same as that of the piston near TDC and BDC.  (They would be identical in all positions for an infinitely long con-rod. The entire rod is travelling upward and has to be decelerated, brought to a stop, and then accelerated downward.  And vice-versa at BDC.)

For the purpose of crankshaft balance calcs, a portion of the con-rod (i.e., the big end) is considered to be rotating mass.
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wobblywalrus
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« Reply #131 on: April 21, 2010, 10:26:18 PM »

When I started doing this I used the entire rod mass as reciprocating weight in the calcs.  A fellow told me that the rod big end is being swung around rather than pushed downward and stopped suddenly.  He convinced me to do calcs using both rotating weight and reciprocating weight.

I dug out the old article by Vincent and he says in the topic "The Limits of Piston Speed and Acceleration" the following:  "Fortunately, we have evolved a formula, as shown just above, which enables the maximum inertia loads at TDC to be calculated with accuracy, the weight W being the weight of all reciprocating metal beyond the section being calculated.  In the case of piston-pin bearing calculations it is the weight of the piston and the pin, except the pin is ignored for the loads on the bearings in the piston bosses.  For the big end, the weight of the connecting rod is also added in."

Vincent's formula was going to be on the third page of these calcs.  Clearly I was using it incorrectly and making things extra complicated.  Interested Bystander, thanks for telling me this.  A revised Page 1 will follow.
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wobblywalrus
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« Reply #132 on: April 22, 2010, 12:59:02 AM »

The entire connecting rod and piston mass is reciprocating mass, and it is listed as such on the new Page 1.  Additional input into Vincent's inertia equation is on Page 2.

The 123 mm connecting rod length and the 68 mm stroke are listed on Page 2.  The connecting rod length divided by the stroke is 123 / 68 = 1.81.
This is the connecting rod ratio and it will be discussed in more detail in subsequent posts.  It is important for engine tuning.

The relationships between connecting rod ratios and engine performance are discussed in the article "Torque and Horsepower" by Donny Petersen in the June 2010 American Iron magazine.  This issue also has an article about the BUB meet and a nice piece about dyno tuning.  It is on the newsstands now.




* New Page 1 Load Calcs.jpg (79.33 KB, 336x441 - viewed 193 times.)

* Page 2 Load Calcs.jpg (70.93 KB, 336x442 - viewed 203 times.)
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wobblywalrus
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« Reply #133 on: April 22, 2010, 11:55:14 PM »

This third page is the maximum inertia equation from Phil Vincent's article.  The equation illustrates an important aspect of the inertial forces on the rod bearings and other parts of the connecting rod/piston assembly.  Inertial loads vary in a geometric ratio to the inertia constant, the crank radius, and the reciprocating mass weight, and the loads vary in an exponential ratio to engine rpm.

A stroker crankshaft is made for these bikes.  I could use this crank with the standard length connecting rods and special 865 cc pistons.  The gudgeon pins in the custom made pistons would be 3.2 mm closer to the piston crown than it is with the standard pistons.  The stroker pistons would weigh the same as the forged 865 cc pistons.  This option is analysed in the example.  The example shows that a stroke increase can cause greater inertial loads at a given rpm.



 


* Page 3 Load Calcs.jpg (78.62 KB, 336x440 - viewed 197 times.)
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« Reply #134 on: April 24, 2010, 01:04:42 AM »

The calculation results are summarized.  Currently I am focusing on connecting rod reliability, and especially on the connecting rod lower end bearing. My plan is to use the standard Triumph connecting rods and to swap them out for new ones every ten runs.  My target rpm is 7,500 and red line is 8,400 rpm.  The percentages are all of the options compared to the inertia loads from the 790 cc pistons at 7,500 rpm.  I know the engine condition at this rpm with the 790 pistons.

First, I look at the 865 cc cast pistons.  They weigh the same as the standard 790 cc pistons and they do not increase inertial loads.  The loads at the 8,400 rpm red line are 26 percent higher than they are at the target rpm.  I am comfortable with this setup and the boxes are highlighed in orange.  The white bearings and chamfered oil holes will make it reliable.

Now, I examine the 865 cc forged pistons.  They are slightly heavier than the cast ones.  The inertia loads at 8,500 rpm is 29 percent higher than the 790 cc pistons at the target rpm.  I will reprogram the rev limiter to lower the red line 100 rpm to 8,300.  Now the maximum inertia loads will be the same as the 790 cc engine.

My 947 cc stroker crank idea using the 865 cc forged pistons is next.  The inertial loads are far higher.  This is a dangerous setup and the boxes are highlighted in red.  There is a possibility of broken rods, pistons, etc.  I do not want to go there.  Some of this higher inertia is due to the piston accelerating harder to travel the longer stroke.  The rod length to stroke ratio of the stroked engine is 123 mm / 74.4 mm = 1.65  This is lower than the standard engine rod length to stroke ratio of 123 mm / 68 mm = 1.81  Engines with low ratios tend to have high piston acceleration rates and other characteristics that are not good for a LSR motor.  I am not literate enough to explain this.  See http://ftlracing.com/tech/engine/rsratio.html  The stroker crank idea will not become reality.

Now the 994 cc big bore kit.  This option provides a lot of extra displacement with minimal increases in inertia loads.  There is a 9 percent increase at the 7,500 rpm target.  I can set the rev limiter to 8,000 rpm.  This will limit the inertia load at red line to 25 percent higher than the 790 cc pistons at 7,500 rpm.  I can live easily with this lower redline in exchange for a lot more power.  I like these big jugs.  This will be a future hop-up if I find the money.

My 750 cc small bore screamer is next.  There is a small decrease in inertial loads as compared to the 790 cc setup.  There will be a lot less power.  This idea seemed good when I thought about it, but the calculations show otherwise.

A fellow racer said "wind that sucker up to 9,000 rpm and it will haul a__"  The inertial loads at this rpm are much greater than at the lower engine speeds.  Carillo rods will be needed, the engine will must be torn apart after every race for rod bearing inspection, and cam chain life will be short.  Nine grand is an option for a dedicated racer with lots of time and money.

The white bearings, chamfered oil holes, relatively light 865 cc pistons, 7,500 rpm target, and 8,300 rpm red line will give me the rod big end bearing life that I need.  Now it is time to figure out the fourth of five reliability issues, the rod little end.       


* Page 4 Load Summary.jpg (56.48 KB, 431x336 - viewed 204 times.)
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