11 replies to this topic

[gray chandler]

1969 Harley Davidson XRtt 750 [ cast iron engine ]
Factory bike at Phillip Island Post Classic event before a camshaft bearing failure. Bike now in the U.S. with Team Obsolete.

Yours truly testing at Mallala on the replica. [ cast iron engine ] Apart from a couple of normal Harley oil leaks it ran well all day.

Edited by gray chandler, 03 January 2011 - 05:30.

[Russell Burrows]

Beautiful indeed. Perhaps you could give us some history/provenance etc?

Edit: Ah, just read your earlier post. Not exactly an unobtrusive motorcycle, particularly in Australia, so I would have thought some information will turn up. Good luck.

Edited by Russell Burrows, 27 December 2010 - 11:37.

[billbomann]

Not an Aussie Harley, I think this one was sponsored by Pratt's of Greenwich. Dave Hughes launches his Harley on Ballaugh Bridge, 1975 TT.

It is rumoured this was not Dave's favourite TT mount!

[gray chandler]

Built this some years ago. If anybody knows of its whereabouts please contact me.

Edited by gray chandler, 03 January 2011 - 04:58.

[Quixotic]

Ahhhhh those tyres look like V Rated Pirelli Sportscomp 2 Phantoms.........

I used to run them on my Benelli Tornado Post Classic Racer....... Back in about 90-91 ish

[Quixotic]

On closer inspection....... No they don't......... Nothing like them......... Bridgestones perhaps?

[gray chandler]

On closer inspection....... No they don't......... Nothing like them......... Bridgestones perhaps?

Michelins, John.

[EngineCon]

Here is some information you may find interesting. This was an answer to a post on another web site.

Here is part of a response to a post on another forum that explains how the Harley racing department when from the single carb 'Y' manifold used on the 1970 Iron XR750 to a two front head, dual carburetor, 1971 Iron XR750.

A statement was made in a post that said… “Honda DID cause HD to make the inlet ports smaller instead of the "too large" that they were until Honda came along”. Read below and you will see that while some may have believed this to be true, it was not an accurate statement.

Here is some history on the engine design approach the HD racing department used in development of the 750 V-Twin.

The smaller port philosophy actually began in 1970 during preparation for the 1971 Dayton road race. This was thirteen years before Honda’s RS 750 came out, not after.

The 1970 Iron XR 750 suffered from major horsepower loss and engine failure due to excessive engine heat. With the large valve sizes and the production Sportster’s included valve angle of 90 degrees, the piston had an extremely high dome. This resulted in a long flame path and required 50 plus degrees BTC of ignition advance for max power. The longer the fire is lit the hotter the parts will get. This was especially troublesome down the long back straight at Daytona. Something needed to be done to have any chance at a win.

The engine had been previously approved in 1970 and therefore could only be modified without any changes to the approved castings other the machining. If new casings were needed, they would have to build 200 complete XR 750’s and get them approved to be able to race.

Matt Kroll (Project Engineer), John Pohland (Engineer) and Peter Zylstra (Design Engineer) proposed major modifications to the existing iron engine using good engineering processes. Examples were the port and valve sizes as well as the combustion chamber shape.

They started by using two front XR 750 iron cylinder head castings.

The intake valve size was changed from an 1 15/16” (49.2mm) down to 1.65” (42mm). The intake ports had tubes welded in that had an 1.38” I.D. (35mm). This allowed two 36mm (1.456”) Mikuni round slide carburetors to be mounted on rubber hoses. These both were rear facing on the right side like the current Alloy XR 750.

The exhaust valve size was change from 1 ¾” (44.5mm) to 1.38” (35mm). Exhaust pipe diameter was changed from 1 ¾” (44.5mm) O.D. to a thin wall 1 9/16” (39.7mm) O.D., 1.5” (38.1mm) I.D.

The front head used on the rear cylinder had the exhaust port welded shut. A new port that exited on the left side of the engine was machined and tube welded in to extend the port. The engine would now have a front down pipe on the right side and a rear high pipe on the left side.

The cylinder mounting side of the head was counter bored to allow the head to sit on the lip that was machine on the top of the cylinder. This resulted in a much shallower combustion chamber. No head gasket was used like on the Sprint.

The spark plug threads were centrally located between the valves. Champion L series (1/2” reach) spark plugs were used. Ignition advance was 35 degrees BTC.

The iron cylinders had the tops machined down to form a lip, again similar to the Sprint cylinders. The bottoms were shortened and machined round with a small flat left that would sit on top of the crankcase while the round diameter would enter the crankcase.

Through studs were used to mount the heads and the cylinders to the crankcase, again similar to the Sprint and carried over on the alloy XR 750.

The connecting rods were 1” shorter at 6.4375” compared to the 1970 XR engines 7.4375”.

Sprint piston forgings were machined to a 3.000” (76.2mm) diameter. The domes were machined to match the combustion chamber design. The compression ratio was only around 8.5 to 1.

At the 1971 Daytona race Paul Smart qualified number one on the Triumph Trident 3 cylinder with Cal Rayborn qualifying second. Calvin’s top speed was only 142 mph compared Paul’s top speed of 157 mph. Cal had a gear box problem on the 1st lap of the race and had to pit to have it repaired. Later in the season, at Talladega with more development, Cal had a top speed of 165 mph and was faster on top speed then the BSA’s and Triumph’s. While running in second place to Steve Baker’s Yamaha, a piston ring stuck in the rear cylinder allowing oil to fowl the spark plug. The engine did win a road race in the US in 1971. It was at Loudon with Mark Brelsford riding. Cal also used this engine in the Trans-Atlantic Match Race Series in England. With Walt Faulk tuning, Cal won 3 of the 6 races and finished second in the other 3 races.

Hope you found this interesting.

Ron

[gray chandler]

Here is some information you may find interesting. This was an answer to a post on another web site.

Here is part of a response to a post on another forum that explains how the Harley racing department when from the single carb 'Y' manifold used on the 1970 Iron XR750 to a two front head, dual carburetor, 1971 Iron XR750.

A statement was made in a post that said… “Honda DID cause HD to make the inlet ports smaller instead of the "too large" that they were until Honda came along”. Read below and you will see that while some may have believed this to be true, it was not an accurate statement.

Here is some history on the engine design approach the HD racing department used in development of the 750 V-Twin.

The smaller port philosophy actually began in 1970 during preparation for the 1971 Dayton road race. This was thirteen years before Honda’s RS 750 came out, not after.

The 1970 Iron XR 750 suffered from major horsepower loss and engine failure due to excessive engine heat. With the large valve sizes and the production Sportster’s included valve angle of 90 degrees, the piston had an extremely high dome. This resulted in a long flame path and required 50 plus degrees BTC of ignition advance for max power. The longer the fire is lit the hotter the parts will get. This was especially troublesome down the long back straight at Daytona. Something needed to be done to have any chance at a win.

The engine had been previously approved in 1970 and therefore could only be modified without any changes to the approved castings other the machining. If new casings were needed, they would have to build 200 complete XR 750’s and get them approved to be able to race.

Matt Kroll (Project Engineer), John Pohland (Engineer) and Peter Zylstra (Design Engineer) proposed major modifications to the existing iron engine using good engineering processes. Examples were the port and valve sizes as well as the combustion chamber shape.

They started by using two front XR 750 iron cylinder head castings.

The intake valve size was changed from an 1 15/16” (49.2mm) down to 1.65” (42mm). The intake ports had tubes welded in that had an 1.38” I.D. (35mm). This allowed two 36mm (1.456”) Mikuni round slide carburetors to be mounted on rubber hoses. These both were rear facing on the right side like the current Alloy XR 750.

The exhaust valve size was change from 1 ¾” (44.5mm) to 1.38” (35mm). Exhaust pipe diameter was changed from 1 ¾” (44.5mm) O.D. to a thin wall 1 9/16” (39.7mm) O.D., 1.5” (38.1mm) I.D.

The front head used on the rear cylinder had the exhaust port welded shut. A new port that exited on the left side of the engine was machined and tube welded in to extend the port. The engine would now have a front down pipe on the right side and a rear high pipe on the left side.

The cylinder mounting side of the head was counter bored to allow the head to sit on the lip that was machine on the top of the cylinder. This resulted in a much shallower combustion chamber. No head gasket was used like on the Sprint.

The spark plug threads were centrally located between the valves. Champion L series (1/2” reach) spark plugs were used. Ignition advance was 35 degrees BTC.

The iron cylinders had the tops machined down to form a lip, again similar to the Sprint cylinders. The bottoms were shortened and machined round with a small flat left that would sit on top of the crankcase while the round diameter would enter the crankcase.

Through studs were used to mount the heads and the cylinders to the crankcase, again similar to the Sprint and carried over on the alloy XR 750.

The connecting rods were 1” shorter at 6.4375” compared to the 1970 XR engines 7.4375”.

Sprint piston forgings were machined to a 3.000” (76.2mm) diameter. The domes were machined to match the combustion chamber design. The compression ratio was only around 8.5 to 1.

At the 1971 Daytona race Paul Smart qualified number one on the Triumph Trident 3 cylinder with Cal Rayborn qualifying second. Calvin’s top speed was only 142 mph compared Paul’s top speed of 157 mph. Cal had a gear box problem on the 1st lap of the race and had to pit to have it repaired. Later in the season, at Talladega with more development, Cal had a top speed of 165 mph and was faster on top speed then the BSA’s and Triumph’s. While running in second place to Steve Baker’s Yamaha, a piston ring stuck in the rear cylinder allowing oil to fowl the spark plug. The engine did win a road race in the US in 1971. It was at Loudon with Mark Brelsford riding. Cal also used this engine in the Trans-Atlantic Match Race Series in England. With Walt Faulk tuning, Cal won 3 of the 6 races and finished second in the other 3 races.

Hope you found this interesting.

Ron

Ron,correct on every count.When Bob Jolly [sadly deceased] and i built the replica we liased with Dick O'brien ,Harley Davison race boss.He exclaimed ''why the f---k would you want to build cast iron engine''.My reply.Down here we run methanol and our compression was 10.0:1+, never had any heat related problems.He was excited that somebody go to that much trouble. I spent days with heating torches and copius ammounts of bronze rods filling in the inlet,exhaust and combustion chambers,took me ages to recover from the fumes.Luckily we had an original XR750tt to copy plus all the factory data compliments of Robert Ianucci[Team Obsolete] who also supplied rotating assembly and gear cassette.[J ratios from memory].The sound of that 750 at over 7000 rpm was music to the ears.I could go on forever but i only type with one finger. I really miss that bike. regards,gray chandler/

Edited by gray chandler, 16 March 2011 - 11:50.

[EngineCon]

Gray,

As a note, in practice Cal's bike at Talladega in 1971 turned 8400 RPM in forth gear with a 3.74 overall gear. For the race the gearing was changed to a 3.63 and maxed out at 7900 RPM in forth gear.

The cams that were run at the first three races in 1971 were modified Sifton ‘A’. As you already know, due to using two front heads, the cam lobes for the rear cylinder must be swapped. The original #1 exhaust now needs to be an intake and the original #2 intake now needs to be an exhaust. The Harley race department did this by copying the ‘A’ profiles switching intake and exhaust using their cam grinder for #1 and #2 cam gears.

A revised set of cams was used from the Kent, Washington race on, which included Talladega. I made this set of cams using four #3 Sifton ‘A’ front intake lobes. This changed the exhaust timing and lift as follows’.

Original Sifton ‘A’ Cam Timing

Intake Open 33 BTC Close 54 ABC Lift @ Valve .425” @ Tappet .300”
Exh Open 47 BBC Close 23 ATC Lift @ Valve .390” @ Tappet .276”

Change Cam Timing using four #3 Sifton Intake lobes

Intake Open 33 BTC Close 54 ABC Lift @ Valve .425” @ Tappet .300”
Exh Open 65 BBC Close 22 ATC Lift @ Valve .425” @ Tappet .300”


Many people believed the 1971 factory iron engines suffered from the same heat problems that 1970 engines did and the alloy engines that came out in 1972 corrected this. The 1971 iron engine used what is called a Half Keystone top compression ring. This ring was designed for two stroke gasoline and diesel engines where ring sticking is a problem. The tapered side causes the axial clearance to vary as the ring moves radially, and thus reduces ring sticking. It seals extremely well (less then 1% blow-by) due to the combustion gas force acting on the tapered top surface as well as the back of the ring. The first 1972 alloy engines used this ring also and on the mile dirt tracks there would occasionally be the same rear piston problem that Cal's iron engine suffered at Talladega in 1971. The looseness that is good for keeping the ring groove clean is not reliable at high piston speeds. This was corrected by using a piston with a conventional rectangular top ring.

Harley learned an enormous amount from the two front head iron engine effort and applied this learning to the 1972 alloy engine.

I would like to commend you on your effort in duplicating this iron engine. I’ am not sure the readers of your post realize the enormous amount of work it takes to complete a project like this.

Well Done!

Ron

PS Here I am with Cal at Daytona on the alloy XR 750. I train my riders right!

[philippe7]

Welcome to the forum Ron. Obviously you were close to Cal Rayborn at some stage so would you maybe care to contribute to this thread we have opened about Cal ? Your first hand insight would certainly be a very valued addition. Thanks in advance . The link to the thread is http://forums.autosp...howtopic=109584

[gray chandler]

Gray,

As a note, in practice Cal's bike at Talladega in 1971 turned 8400 RPM in forth gear with a 3.74 overall gear. For the race the gearing was changed to a 3.63 and maxed out at 7900 RPM in forth gear.

The cams that were run at the first three races in 1971 were modified Sifton ‘A’. As you already know, due to using two front heads, the cam lobes for the rear cylinder must be swapped. The original #1 exhaust now needs to be an intake and the original #2 intake now needs to be an exhaust. The Harley race department did this by copying the ‘A’ profiles switching intake and exhaust using their cam grinder for #1 and #2 cam gears.

A revised set of cams was used from the Kent, Washington race on, which included Talladega. I made this set of cams using four #3 Sifton ‘A’ front intake lobes. This changed the exhaust timing and lift as follows’.

Original Sifton ‘A’ Cam Timing

Intake Open 33 BTC Close 54 ABC Lift @ Valve .425” @ Tappet .300”
Exh Open 47 BBC Close 23 ATC Lift @ Valve .390” @ Tappet .276”

Change Cam Timing using four #3 Sifton Intake lobes

Intake Open 33 BTC Close 54 ABC Lift @ Valve .425” @ Tappet .300”
Exh Open 65 BBC Close 22 ATC Lift @ Valve .425” @ Tappet .300”


Many people believed the 1971 factory iron engines suffered from the same heat problems that 1970 engines did and the alloy engines that came out in 1972 corrected this. The 1971 iron engine used what is called a Half Keystone top compression ring. This ring was designed for two stroke gasoline and diesel engines where ring sticking is a problem. The tapered side causes the axial clearance to vary as the ring moves radially, and thus reduces ring sticking. It seals extremely well (less then 1% blow-by) due to the combustion gas force acting on the tapered top surface as well as the back of the ring. The first 1972 alloy engines used this ring also and on the mile dirt tracks there would occasionally be the same rear piston problem that Cal's iron engine suffered at Talladega in 1971. The looseness that is good for keeping the ring groove clean is not reliable at high piston speeds. This was corrected by using a piston with a conventional rectangular top ring.

Harley learned an enormous amount from the two front head iron engine effort and applied this learning to the 1972 alloy engine.

I would like to commend you on your effort in duplicating this iron engine. I’ am not sure the readers of your post realize the enormous amount of work it takes to complete a project like this.

Well Done!

Ron

PS Here I am with Cal at Daytona on the alloy XR 750. I train my riders right!

Thanks Ron!,This was an accidental project.I visited Bob Jolly looking for a vane type supercharger he manufactured. He had a Manx Norton 500.a 880 JAP in a Featherbed frame and several other customer race bikes. Laying against the wall was a XR750tt which was awaiting restoration for Robert Ianucci.It had been in Australia for a few years.I asked if it was possible to obtain one''.Hell No''! .you will have to build one. Well 5 years later and travelling a 100mile round trip every weekend and sometimes thru the week we finished it. Had some interesting conversations with Mert Lawill,Jay Springsteen and Dick O'brien.Dick was a true inspiration. As a side note regarding the engineering side of the bikes,the factory bike suffered a catastrophic cam support bearing failure.These bearings were a ball race type and i suspect failed due to the high spring pressures. On my engine the camshafts we had made here had larger shafts so we could use a torrington needle roller bearing,but we had machine the case to suit.Never had a failure!!!.I have a ton of photographs of this project that i could scan. You can email me at graychandler@bigpond .com .. regards,gray chandler.

Edited by gray chandler, 15 March 2011 - 10:09.