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  #11  
Old 1 Week Ago
needspeed needspeed is offline
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Quote:
Originally Posted by kitabel View Post
S&S breather instructions for IH stroker:
1. use 1972-76 rotor
2. only port pump tower to .419" wide
3. duration 227° total
Just to avoid confusion: When opening the tower slot it should only be done on the closing side.
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  #12  
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I always use the -72 oil pump simply because it has the largest scavenge gears.

I don't go to any great lengths to alter the breather timing.

I know Obrien spent a lot of time with this. I think he worked out having the opening point at 27 Degrees ATDC was the optimal point and advocated shimming or grinding of the gear to get it spot on.

The problem stems from having oil in the crankcase being dragged around by the flywheels. And we know this can be a problem in some engines.

Later on the mini sump obviated the need for this.

They also ran 1/4 speed oil pumps to reduce the flow rate.

Stock Sportster engines feed oil through the end of the crank. And that works well.
In fact, a bit too well.

S&S cranks come with a screw in restrictor so you can reduce the oil fow to the big end if you want to. I use them.

And OB was doing this on much higher revving 750's that were running at Daytona.

How many of us hold the throttle wide open for that amount of time ?

When the revs drop off the system will catch up with any excess oil down there.

Now I could always be wrong about this. But I have never noticed a power loss at the end of any straights I have encountered. Caveat here as I haven't been able to run at Phillip Island. (They don't run Historic sidecars there any more)

If it was a concern I would also run external top end oil lines and feed directly into the gear cover.

I DO run a PCV valve on my breather. I wondered when I first did it if it might effect the normal oil return system which relies on the pumping pressures inside the cases.
But they run them on the XLCR's and that was good enough for me.

But of course, I could always be wrong.
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  #13  
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Oh. Nearly forgot.

Cylinder lengths. I missed the bit about their height.

But normally when you build an engine like this you skim the cylinders anyway. This height is part of how you set your effective compression ratio. Depending on factors like the piston you choose, cams etc this needs to be "juggled".

When you get really serious you do away with the base and head gaskets as well.

Using stock length cylinders and the 3.00 JE pistons for strokers if you "clean up" the gasket surfaces and run gaskets and run a 4 - 5/8 stroke you will most likely end up with a compression ratio that's a bit high for use on the street.

The minus minus cams will help you start it but it's going to rattle.

Won't have EFI and an engine management system on this engine which was designed back when 100 proof gas was everywhere.

Maybe at 10,000 feet on a chilly winters day it's ok.

At sea level on a hot day .... not so much.
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  #14  
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Quote:
Originally Posted by Ferrous Head View Post
I DO run a PCV valve on my breather. I wondered when I first did it if it might effect the normal oil return system which relies on the pumping pressures inside the cases.
But they run them on the XLCR's and that was good enough for me.
The one way breather valve (foo-foo) is part of the stock system on the mini sump - non breather valve XLCR. So just because a PVC works on the XLCR it doesn't necessarily mean it will work on your engine with the timed breather.

It might help or it might not or it might not make any difference. Do you notice any difference with it or without it?
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The only way I think I could really measure any changes would be to do back to back dyno runs.
But I have always run PCV valves on my race bikes.
It helps to reduce crancase pressure which I believe is a good thing.

But it also helps with oil leak prone engines. Helps keep the oil in. I think.

This is probably another one of those "I can get 1/4 hp more by polishing the inside of the cases or 1/4 hp more by lapping in the geaarbox.

Guys like OB went the last few yards because they had to compete with other racers who had basically the same engines. So he spent countless hour hand crafting every part and chasing down that last 1 hp. Diference between a stock as delivered KR and one of his engines was probably 4 hp. Not much, but enough in a race.
Unless of course your opposition has Cal Rayborn riding for them.

There was a legendary Norton tuner by the name of Francis Beart.

He installed new wheel bearings in his wheels. Then set them up with an electric motor and a belt to run the wheels for 24 hours.
That basically lapped in the wheel bearings.
Added to all the other tiny improvements he made his bikes won at the Isle Of Mann on a very regular basis.

I believe it was Giulio Carcano who in the 1950's instructed his team to pull their race bike apart and study every single part. His instructions were to make it lighter.
They did. Even reducing the size of the spoke nipples.

Despite not improving the (rather old) engine design Moto Guzi dominated the middle weight classes in Europe for years afterwards.

Little things do add up but none of that matters when I'm running an engine that starts out 200 cc's bigger than theirs and can be built into a 1365 cc behemoth. There is just no way their poor little 650's can be stretched to that size. I'm not cheating I just read the rule book and acted accordingly.
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the XR-750 uses a one way breather valve in addition to the timed breather.there is a hole tapped into the case behind the rear cylinder. Gene did you see the -54R KR/XLR connecting rods listed by another seller? here's a link https://www.ebay.com/itm/Harley-Davi....c100667.m2042 they're for a ball bearing motor but you don't see them often.kind of rare.
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Not KR or XLR parts. They are rare and expensive things to really go racing with.
And normally they are not available as NOS.

S&S just make it too easy and cheap to build a stroker engine. When you can buy a complete rotating assembly with shafts that is balanced to whatever you want before you receive it why would you do it yourself ?

Stronger rods aren't really necessary. You can quite happily use the stock Sportster rods. In fact the S&S rods are a little heavy. If your using them and going to balance the wheels I would suggest taking some metal off the little end area.

I don't like using stock wheels in a racing application. They are cast iron and have been known to break under race conditions. But the rods are fine.

But when you look at the cost of putting a set of wheels together and paying for the balancing it's hard to save a great deal of money. Especially if you pay someone else to assemble and true which most of us do. Add in S&S shafts (some of the wheels have a different taper) and big end parts and it quickly gets close to just buying a new assembly. Also consider the unknown quality if the tapers inside used wheels and I just don't bother anymore.

If your seriously tryng to build a race style engine you aren't constrained the way Harley was with their KR's and XLR's.

And I build to my class rules. If it allowed superchargers it would be on there.

And when I say this is cheap it is compared to trying to start with what my competitors mostly use. triumphs, Nortons and BSA's. A race crank for them starts at 3 grand and that's if you can find one. For all out racing they need billet cranks. That's before they buy rods and have it balanced.

Biggest parallel twin engines I'm aware of in my class is a Maney Norton at 1105cc. Those engines will set you back over $25,000. No one here races them.
And why would you when you can build a Sportster engine that will blow it into the weeds for leas than a third of that.

Smokey Yunick.
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  #18  
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Well that auction was fun. Everything appears to have sold. I guess my 69's going to grow a couple inches. How many I'm not exactly sure. What does 4 and 5/8 stroke make a 900?

Last edited by RicThompson; 1 Week Ago at 01:37.. Reason: add question
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A little over 65 cubic inches (65.38 I think).

Congrats on the win. The benefits from the increase in size are a bit more than you might imagine.

The ports on the 900 engines were a little big to start with. Boosting the engine size in this way affects the port velocity and makes them work "better".

It's a shame you didn't manage to grab the cams as they make life a lot easier with a stroker that you run on the street.

But once you have the whole thing together and going it will be like the first time you ever rode an Ironhead in your life. Big grin.
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Quote:
Originally Posted by Ferrous Head View Post
A little over 65 cubic inches (65.38 I think).

Congrats on the win. The benefits from the increase in size are a bit more than you might imagine.

The ports on the 900 engines were a little big to start with. Boosting the engine size in this way affects the port velocity and makes them work "better".

It's a shame you didn't manage to grab the cams as they make life a lot easier with a stroker that you run on the street.

But once you have the whole thing together and going it will be like the first time you ever rode an Ironhead in your life. Big grin.
Thanks. I was guessing about 10 inches 4 and 5/8 adds about an inch of arm. The 1969 I'm working with has PB cams in it and Jerry Branch heads. I've added a refurbed mag, an S&S Super B with Yost Power Tube and 1 inch manifold spacer.
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