Ironhead Shovster build take2

[RicThompson]

You killed a set of 4 and 5/8's flywheels? AAAHH. A moment of silence please.

[billeuze]

Originally Posted by Ferrous Head

Paperweights ?

If it helps any, with the 4.5 inch wheels you don't actually have to move the oil holes.

Ha, no doesn't help as I have no oil holes in my shovster cylinders, I'll have to use external oil returns

And in theory the shorter stroke will allow higher revs which the Shovel Heads will be able to feed.
You should probably always skim alloy heads in any case so not really any extra cost there.

With the alloy heads you can up the compression more than you can with the cast iron Sportster version.

How much to take off ?

Dunno about that with Shovel heads. I would do a dry assembly and do a measure. Your also going to need to cc the combustion chamber to get a ball park figure.

It's not going to be "Super" critical either way. Too little of and you wind up with less compression than is optimal which you can correct by skimming again.
Too much can be alleviated by running thicker head gaskets.

The real go would be to try for some quench area. Then accept whatever clearance is required for that.

[billeuze]

Originally Posted by kitabel

Diameter of stock sportster flywheels = 7-7/8"

Were you going to re-clock the rocker arms?

I don't know, what does that mean?

[billeuze]

Originally Posted by RicThompson

You killed a set of 4 and 5/8's flywheels? AAAHH. A moment of silence please.

Yes, the poor buggers ended their useful life far too early, sigh!

[gobowept]

I've had a bad experience order car accessories from eBay. The quality was just so poor.

[billeuze]

Originally Posted by kitabel

The RPM difference between 4-1/2" and 4-5/8" at the same level of inertial (tension) stress isn't 4.500 ÷ 4.626 (2.7%). It's its square root, or 1.4%.

The shovel rocker arms all "point" at a central cam core (as do all single-cam pushrod engines), each base circle and lobe occupy the same position. The Sportster cams are in 4 different places (as are all 4-cam engines), and are now at the wrong angle for proper rocker arm geometry.
This is not an adjustment, it requires surgery, specifically cutting one lever (usually the pushrod end) off the rocker shaft and re-orienting it to point to its cam lobe, and welding it up.
All 4 rockers should be modified, resulting in 2 different mirror-image angles: intakes will have a smaller correction than exhausts, and front & rear cylinders will be opposites. Baisley has probably done this.

Hmm, No that job was not on my radar. would it not run OK without said surgery? It is not a race engine. I see what you mean, the angle would be off by a few degrees, exhaust worse than intakes. But even so the pushrod end fits in a socket and should not pop out. And its not perfect anyway, the pushrod goes up and down while the rocker rotates on an arc and the vector of the "push" changes as the rocker rotates back and forth. But yes, the starting point of the "push" would be a bit inward from the ideal starting angle, and the angle when the valve is fully open would probably be better.

[rokytnji]

Probably somebody who built and owns a shovster without the mod would be the best answer.

Probably rare as hens teeth.

[Ferrous Head]

The RPM difference between 4-1/2" and 4-5/8" at the same level of inertial (tension) stress isn't 4.500 ÷ 4.626 (2.7%). It's its square root, or 1.4%

Granted, it's not a lot more.

But when running a rev limiter you might just feel that little bit better about setting it at 6500 instead of 6 where you know it will be safe.

There's no doubt the Shovel Heads breathe better than Iron Sportster junk. EWrrr.... heads. And being alloy you can afford to go higher on the compression ratio. If your going to go to all that trouble to adapt Shovel Heads you are probably looking for HP as much as torque and you'll want to spin it to take edbantage of them.

Well, I would.

[mrmom9r]

FE you're dead wrong about Shovel vs IH airflow.

[Ferrous Head]

Oh ! I was under the impression the Shovels did a lot better.

I've never ever played with them, so no real idea. When I think about it, it might just be an assumption of mine.

I thought they put a fair bit of effort into those heads after having problems with th Pans. Being designed a lot later than the Ironheads I can't imagine why they wouldn't be a better bet. I would have thought at the very least having to feed a 1200 as opposed to a 900 the port sizxes would have been bigger to dtart with. Though I know bigger does not always mean better.

I know the poor geometry of the push rods versus rocker arms is one thing that limits how fast you can rev those poor old things. And I'm pretty sure everyone who builds a Shovester cuts the rocker arms.