"Old School Standard Headwork"

[JamesButler]

I just picked up a '92 FXRS-Convertible (two-tone poppy) with 19K miles/  S&S carb with thunder jet.  The 2nd owner who sold it to me had very little knowledge about the bike - probably the reason I got it for  such a good price. 

Anyway, in the owners manual which he provided, the original owner had stapled a card with some info on the inside cover: "Heads milled .080" in August '96.  Spring clearance .530".  Int. 1.900", Exh. 1.630", PM valves, Andrews springs and collars."

In an attempt to show his "knowledge" about the bike, the guy tells me it's "Old school Harley dealership headwork".  He was parroting something he had been told, but it's all good.  Got me thinking though...

So, for you "old-school" head experts who can remember back 20+ years ago, was milling the heads .080" common Standard Operating Procedure dealership practice back in the mid 90's?  Was this practice part of a common build?  If so, what would be the common head gasket thickness, what cam?  Without opening up the cam chest, I'm assuming a mild cam was installed - maybe an Andrews EV-27, EV-3 or EV-35 since the collars and springs are Andrews, and they were / are popular FXR cams. 

Would milling .080" off the heads match up with an Andrews 27, as far as acceptable compression ratio, or does the fact that the spring clearance was opened up to .530" suggest a larger than bolt-in cam could be in there?  BTW, shaving .080" off of the heads seems like a lot to me, especially for a dealership.

[JamesButler]

Did a little research.  According to some "older Andrews catalog info", .080" bumps the comp ratio to from stock 8.5: 1 to 9.73: 1. 

I'd guess then that if an Andrews cam is in there, then it would be an EV-46.  Still a bolt-in cam. With a 41º intake closing angle, it would "correct" c.r. to 9.00: 1. 

[Hossamania]

How does it run?
I can't help with the headwork, but I can tell you that the EV46 is one hell of a cam. It works ok at low and midrange, especially with a bump in compression, but it pulls like a sonofagun in the upper third. No EV27 stands a chance against it.

[wfolarry]

Old school for me was a .050 cut with an EV 27.
Lots of shops milled the heads to gain compression because it didn't cost much & the piston choices weren't that great IMO.
Nowadays with so many pistons to choose from [& better fitting] a piston change is usually the first choice unless the bump you're looking for is small.

[prodrag1320]

.060 is as far as I want to go as far as milling heads (and don't like milling that far).we`ve always used pistons to raise compression for 35+ years.also am kind of scared anytime "old school" is used to describe anything

[Burnout]

Milling the heads is a cheap easy button mod.

Ideally you should work on the cylinder first, there is more CR gain from the same amount of material removed.
Up until the piston starts hitting the head. Then you "Thunder Storm" it.

The EVO's claim to fame is the squish band, maximizing that feature improves power, efficiency, and resistance to detonation.

Any guess as to what cam is installed would be, well, a guess.

Take it apart and see what you have, unless you are just looking for bragging rights at the watering hole.

[masstch]

Up until the piston starts hitting the head. Then you "Thunder Storm" it.

OK, I'll ask, whazzat mean?

[prodrag1320]

Up until the piston starts hitting the head. Then you "Thunder Storm" it.

OK, I'll ask, whazzat mean?

I think he`s talking about machining the cylinder instead of milling the head,this is fine to achive a 0 deck height,but should never be machined more than that.machining the cylinder until the piston protrudes out the top & hits the head is what he`s meaning by "thunder storm" (about what I can gather from it,ive never heard the term before either).milling the head combined with domed pistons is defanatly the way to go for the compression your looking for (with machining the cylinder for 0 deack,but no more than that)on a street motor,its never a good idea to run less than .030 squish

[Burnout]

Google "thunder storm harley"

The thunderstorm setup takes the squish band to a higher level

[JamesButler]

Old school for me was a .050 cut with an EV 27.
Lots of shops milled the heads to gain compression because it didn't cost much & the piston choices weren't that great IMO.
Nowadays with so many pistons to choose from [& better fitting] a piston change is usually the first choice unless the bump you're looking for is small.

larry, I was thinking the same.  Makes me feel like I know what I'm talking about when I'm thinking along the same lines as you...

.060 is as far as I want to go as far as milling heads (and don't like milling that far).we`ve always used pistons to raise compression for 35+ years.also am kind of scared anytime "old school" is used to describe anything

Agreed, I too thought .080" was a lot.

How does it run?
I can't help with the headwork, but I can tell you that the EV46 is one hell of a cam. It works ok at low and midrange, especially with a bump in compression, but it pulls like a sonofagun in the upper third. No EV27 stands a chance against it.

Only rode it for about 20 miles. Ran fine, but I didn't get it over 70 mph / 3,100rpm, so didn't really test the cam or the Thunderjet.

Since the 46 "pulls like a sonofagun" in the upper third, I suppose it makes sense then that the Thunder jet was installed into the Super E as part of the build.    However, other than shifting at 4,000 rpm, I don't really get the rpm above 3,500 when cruising. 

Normally, this wouldn't be my build of choice, but the bike was available at such a good price, including an extra set of 13-spoked mags, an extra Mustang seat (for FXR), a newish H-D full face helmet, matte grey half helmet, fair-condition convertible saddlebags, cover, and being located only 15 mins. away from me, it would have been criminally negligent / irresponsible on my end to pass on it.  No flaking or chipping of the back paint on the cylinders, cases or heads.  It's really clean

I Definitely don't need this (fourth) FXR in my shed.  Probably didn't need my third FXR, either. So, I'll clean this one up and either flip it or my stock '93-convertible on CL or one of the FXR Facebook sites...

Milling the heads is a cheap easy button mod.

The EVO's claim to fame is the squish band, maximizing that feature improves power, efficiency, and resistance to detonation.

Any guess as to what cam is installed would be, well, a guess.

Take it apart and see what you have, unless you are just looking for bragging rights at the watering hole.

Yep, only speculating on the cam based on the facts that were presented to me.  Definitely will not be not taking it apart to find out what's in it, as I will be flipping it.
   

[Hossamania]

If it runs good and has the power where you want it, I wouldn't mess with it until it blows up.

[Hillside Motorcycle]

Yep.
"Cam and a haircut" build back in the day.
EV-27's, 3's, and Wood 6's.
Quick dyno tune. Done.
Just think, this was being done prior to the internet.....hahaha!

[jbexeter]

Yep.
"Cam and a haircut" build back in the day.
EV-27's, 3's, and Wood 6's.
Quick dyno tune. Done.
Just think, this was being done prior to the internet.....hahaha!

Probably also "prior to CNC"... always remember an old machinist that used to do head work, he had to "50 thou" shims for setting up the mill for a head skim, one was for triumphs and one was for norton and bsa, of course neither one was spot on 50 thou, , one was a little light and the other one was a litle heavy, always remember the "pass me the 50 thou shim, no, not that one, the other one..."

[thumper 823]

I have at least .080 off
Reworked chambers.
a for real 10.5 C/R  high dome pistons
.030 squish band
double plugged.
And i might add it does run.

[JamesButler]

I have at least .080 off
Reworked chambers.
a for real 10.5 C/R  high dome pistons
.030 squish band
double plugged.
And i might add it does run.

I was aways curious about the dual-plug concept and application. Seems like it's also more of an "old-school" technique. What brand pistons are they, and when was your work done?  Not sure what pistons are in this FXRS-convertible that I just picked up.  I'm assuming they are stock - just as I'm assuming the cam is an Andrews EV-46.  Purely hypothesis. Similarly, I'm also not sure what the HG thickness or squish are either.  If I don't sell it, then eventually I'd open it up to find out.

[Burnout]

Dual plugging is the most beneficial with a poor combustion chamber.
It is not old school, it is a way to improve old style combustion chambers.
Modern combustion chambers do not benefit as much from dual plugging.

The best example is an Ironhead, a worse combustion chamber than a flathead even.
A large Hemispherical chamber a large pop up piston and the spark plug located way off to the side.
No squish band to stir up the charge, and the flame has to travel around the piston to light the mix on the other side.
This is why Ironheads like so much spark advance, it takes so long for that flame to travel around the piston, you have to light it early.
The problem with this is lighting it as early as it wants is tricky because you are getting into the detonation zone.
When lighting the fuel that early, the piston is still coming up increasing the pressure at the same time the burning fuel is increasing the pressure.
It is very easy to over pressure the cylinder and cause the fuel to explode instead of burning in a woosh.
Dual plugging helps this style chamber because it cuts the burn time in half by lighting the charge on both sides.
This means that instead of 45° BTDC for a single plug, with dual plugs you can have the spark at 35° and make the same power.
But you are 10° closer to TDC which means although the starting pressure is higher the peak pressure happens later which gives the piston time to pass the top and do work instead of making a bomb.
This is an over simplified explanation as there are many other factors such as ambient temps, fuel octane rating, dynamic compression ratio, & more that come into play. 

A Shovelhead has a similar problem, no squish band, and a domed piston (just not as tall as an Ironhead).

An EVO motor fixes most of these combustion chamber problems by having a flat top piston and the "D" shaped chamber.
As the flat piston approaches shelf that is formed by the flat side of the D chamber is squeezes the mixture over at the spark plug.
This turbulence mixes the charge better and gets it all lit way quicker than an Ironhead or a Shovelhead.
This is the most pronounced improvement of the EVO motor and makes it a more efficient producer of power.

Now back to dual plugging,
Due to the highly efficient combustion chamber of an EVO little, if any, gains will be realized by dual plugging, by itself.
For instance, on an EVO with a crazy high compression ratio you might dual plug it to buy yourself a degree or 2 more time to avoid detonation.
In other words you will not see much gain in power, but you would see a gain in reliability and longevity by delaying the spark and not loosing power.

The way to improve an EVO chamber is to weld it up and make a "bathtub" chamber like a Twin Cam that squeezes the mix in from both sides,
or to do a Thunder Storm chamber by using a domed flat top piston with a bevel around the edge and then removing the shelf in the head and machining a bevel in the head that matches the piston.
This creates a squish band that goes almost all the way around the piston which creates a colliding turbulence and concentrates the charge in the center.
Additionally it opens up the chamber like a shovel which un-shrouds the valves and allows better breathing as well.

[JamesButler]

Dual plugging is the most beneficial with a poor combustion chamber.
It is not old school, it is a way to improve old style combustion chambers.
Modern combustion chambers do not benefit as much from dual plugging.

The best example is an Ironhead, a worse combustion chamber than a flathead even.
A large Hemispherical chamber a large pop up piston and the spark plug located way off to the side.
No squish band to stir up the charge, and the flame has to travel around the piston to light the mix on the other side.
This is why Ironheads like so much spark advance, it takes so long for that flame to travel around the piston, you have to light it early.
The problem with this is lighting it as early as it wants is tricky because you are getting into the detonation zone.
When lighting the fuel that early, the piston is still coming up increasing the pressure at the same time the burning fuel is increasing the pressure.
It is very easy to over pressure the cylinder and cause the fuel to explode instead of burning in a woosh.
Dual plugging helps this style chamber because it cuts the burn time in half by lighting the charge on both sides.
This means that instead of 45° BTDC for a single plug, with dual plugs you can have the spark at 35° and make the same power.
But you are 10° closer to TDC which means although the starting pressure is higher the peak pressure happens later which gives the piston time to pass the top and do work instead of making a bomb.
This is an over simplified explanation as there are many other factors such as ambient temps, fuel octane rating, dynamic compression ratio, & more that come into play. 

A Shovelhead has a similar problem, no squish band, and a domed piston (just not as tall as an Ironhead).

An EVO motor fixes most of these combustion chamber problems by having a flat top piston and the "D" shaped chamber.
As the flat piston approaches shelf that is formed by the flat side of the D chamber is squeezes the mixture over at the spark plug.
This turbulence mixes the charge better and gets it all lit way quicker than an Ironhead or a Shovelhead.
This is the most pronounced improvement of the EVO motor and makes it a more efficient producer of power.

Now back to dual plugging,
Due to the highly efficient combustion chamber of an EVO little, if any, gains will be realized by dual plugging, by itself.
For instance, on an EVO with a crazy high compression ratio you might dual plug it to buy yourself a degree or 2 more time to avoid detonation.
In other words you will not see much gain in power, but you would see a gain in reliability and longevity by delaying the spark and not loosing power.

The way to improve an EVO chamber is to weld it up and make a "bathtub" chamber like a Twin Cam that squeezes the mix in from both sides,
or to do a Thunder Storm chamber by using a domed flat top piston with a bevel around the edge and then removing the shelf in the head and machining a bevel in the head that matches the piston.
This creates a squish band that goes almost all the way around the piston which creates a colliding turbulence and concentrates the charge in the center.
Additionally it opens up the chamber like a shovel which un-shrouds the valves and allows better breathing as well.

Wow, fantastic explanation!

[Matt C]

That's bang on right there. 

Welding chambers, it's somewhat of a crap shoot, b/c they will crack at the plug hole if you get em too hot.

Welding them with 80/20 argon/helium mix is the way to go. You can get in and get out quickly without putting a ton of heat into it. Straight argon takes too long to puddle (even with a 350A machine). So the head gets hotter
than f--k by the time you're done. I did a set a while back with straight argon. Minutes after I was done, I heard
this loud "dink".

DOH!

Helium is a must, make sure they use it if you're getting heads welded. Night and day difference as far as
chances of cracking. (you can weld with 200 amps as opposed to 300+. That makes a big difference)

[thumper 823]

I have at least .080 off
Reworked chambers.
a for real 10.5 C/R  high dome pistons
.030 squish band
double plugged.
And i might add it does run.

I was aways curious about the dual-plug concept and application. Seems like it's also more of an "old-school" technique. What brand pistons are they, and when was your work done?  Not sure what pistons are in this FXRS-convertible that I just picked up.  I'm assuming they are stock - just as I'm assuming the cam is an Andrews EV-46.  Purely hypothesis. Similarly, I'm also not sure what the HG thickness or squish are either.  If I don't sell it, then eventually I'd open it up to find out.

Pistons   - JE high dome for real 10.5  CR
Cam  DM 530
About .020 shaved off the bottom off cylinders if I remember correctly (2 years ago) to attain the .030 squish band.
Big bore cylinders with one offset plugs really benefit from adding one more.-For all the reasons listed above and a few more.
A side note-
Jump in and old aeroplane with 1/2 horse per cube (about  70 to 80 CCP)
Shut dwn one set of pugs and watch the RPM drop.
Yes, the extra plugs are for redundancy but it brings some extras to the table also, even with low CR engines.

[Matt C]

"Jump in and old aeroplane with 1/2 horse per cube (about  70 to 80 CCP)
Shut dwn one set of pugs and watch the RPM drop."

When I was flying,
We had to kill the Left then Right magneto with the engine run up to power as part of the check list.
I wouldn't take off if the RPM dropped more than 200 when you killed a magneto.

Also, EGT goes up a little as well when one magneto is shut off (if everything is normal). If EGT went
down, that's a no-go too.


 

[thumper 823]

AND, That "roght" there ought to enough to finalise dual plug argument or not.

I never wished for less spark from my spark plugs ................

[Matt C]

Its mostly a reliability feature, doesn't really give you any more power if everything is working properly.