Head modification

As I'm not familiar with the xj motor, does anyone have evidence showing decent benefit in a very mild port/polish and 3-angle job?

I'm not doing anything serious to this motor, would like to build it as a supreme working stock motor.

The valve cuts and seats look like they could use some better lovin' then my standard lap. Any info is much appreciated.

~Scott~

 

It's my understanding that is one of the few things that can be done to improve performance in stock configuration. These things were very well engineered and only some production-cost constraints kept them from being their 110% best. If Dinoracer doesn't chime in, PM him. He has club racing experience with XJs.

 

I think you will find the Head to have been fairly Ported right at the factory.
Other than a casting blem left-behind; you shouldn't have much material to remove -- Porting wise.

Polishing can never hurt. Have fun bringing the Ports to whatever degree of Finish you feel comfortable with.

As for the Valve and Seat Cut.
Trying to improve on that will only set you up for sucking-up a Valve if you reface the Valve and Seat too steeply.
The Valves are usually cycling at 45-hundred rpm or greater.
Flatter than steeper keeps the Valve on the Combustion Chamber side of the Seat!

That, and the Valve Clearances being adjusted with Shim Discs at close tolerances keeps the Valves within a window of 2 - 5 thousandths. A steeper Cut would close that gap and an OEM Shim might not be available.

 

Do NOT polish the intake.
Make it smooth but leave the finish slightly ( 60 grit catrtrige roll ) rough.

Make the valves, chamber, and exhaust port look like chrome if you want but polishing the intake would cause the fuel to stick to the walls and reduce performance.

The key to porting is:
Maximum velocity with minimum material removal.

If you hog out the ports so you can through a cat through them you will murder the velocity and consequently the low and mid range torque whila not gaining much if any top end.

When in doubt don't touch it.

A three angle valve job ( 30-45-60 degrees) and a 30 degree back cut on the valves can do wonders but don't make the seat too narrow or it will beat the seats to death due to overheating.

Feel free top PM me as I have quite a bit of porting experiance.

 

tech,
I think I've found the first thing that I don't think I could do to my bike...

 

keep the ports small!!!!!

for the size of each cylinder, the ports are too big for the working class engine you want. smooth out any imperfections, but i dont think that will even be worth your time unless you are playing with cams as well.

 

If you're really into it ... and want to get the most you can get out of the Plant; do this.
Mount a Manifold to its spot on the Head with a Gasket in place. Then, reach in the Manifold and FEEL how the three elements "Line-up".
Does the Gasket overlap the inside mating surface.
Is there a "Ridge" between the Manifold and Head that you can shape.

Don't do any work on the Manifold.
You'll just be causing the Rubber Coating to be sanded off.
Not good,
But, if there's a RIDGE at where the Head meets the Manifold ... and, you can reduce the protuberance to allow the two surfaces to join without the edge that would cause turbulence within the cavity.

 

Thanks for all of the good input. I WILL at least port match the intake side to the intake manifold.

As for polishing the combustion chamber...i wouldn't do that. A mirror like finish doesn't allow the formation of carbon based crystals. Polishing the chamber will make for a poor burn and overall not as much power.

 

polishing also eliminates the thin layer of cushion air that allows ports to flow as well as they do.

 

polishing the cylinder lets me run 93 octane on a 14 to1 motor

 

Polishing the Combustion Chambers is something that real Hot-Rod Guys have been doing forever!
For ... a ... long ... long ... time!
It's what separates the men from the boys.

A polished Combustion Chamber wont allow carbon deposits to form.
The polished Combustion Chamber makes the power stroke more efficient.
With a polished Combustion Chamber the Engine is LESS likely to have pre-ignition knock.
The exhaust gases are expelled more efficiently.
The engine runs cooler because nothing forms in the chamber.
Polished Combustion Chambers are found on Race-Prepped Engines of all sizes and ALL materials.
With the right tools and compounds you can put a finish on cast iron.

The only down-side is that if you have to remove a lot of material to achieve the polished surface ... you reduce the Compression Ratio.
Not likely to happen on a near-finished surface found on the XJ-Bike Head.

 

About the only thing I did on the first motor that I built was to put in a set of wiesco 652 pistons in the FJ600 engine and blend the ports to the intake manifolds. Bike made good power was doing 12.0 second runs on the bike. Had a season of roadracing in it and found another 600 engine to build and spent about 1200 bucks doing it. Put in another 652 kit with about $300 of head work which included porting the heck out of that head. Before you could put in a finger and wiggle it around abit. Afterwords you could move it around ALOT!! The intake ports were huge afterwords with polishing done on the exhaust side. I had stock cams in but did alter the timing, had the crank out and balanced magnifluxed for cracking. I also had FJ600 stock carbs but with K&N air filter pods and a stage 3 carb kit with a Spec2 exhaust pipe. Took it to the track and after a short break in period I decided to start hammering it, I pulled in from two practice sessions thinking that I had no 5th or 6th gear. It was pulling like a freight train through all of the gears. Wound up dropping to 11.7 1/4 mile at 104 mph with tall gearing on it for road racing at Willow Springs.The bike made 76 hp on the dyno. The bike ran great and ran it for two seasons without any problems at all and wound up with the vintage dinosaur class champ back in 97. It was the last year that the biks were unlimited displacement and the xj550 kicked everyone's tail. Was fun, sure do miss it like crazy.

 

The picture you showed is not "polished". It still seems to have some texture which is need for formation of carbon crystals which are GOOD for proper combustion. A mirrored polish is bad. Less surface area would reduce thermal efficiency. It would also reduce the efficiency of the quench zone during compression. All of the "hot rod" guys I know work the combustion chambers in order to Increase available quench/squish where appropriate and maintain equal volume in each combustion chamber.

 

dont forget crossflow area for valve overlap, a lot of power can be picked up there.

 

Hey, ... wait a second!

Address cast-aluminum, air-cooled, motorcycle cylinder heads, on "Small" engines, that are classified High-RPM's operated, spark advance LIMITED, and Combustion Chamber operating temperatures dependent upon Air~Fuel Ratio of Fuel Mixtures alone ... and the finish on the Quench Zones don't matter.

Having the area LESS susceptible to collecting build-up from deposits of any nature would be preferable than having the surface collect carbon or other impurities which contribute negatively to the power plants longevity.

 

id have to fully agree with rick, my 13 to 1 motor was pinging pretty bad on 93 octane so i took it all apart, smoothed the valve dishes in the piston, completely polished the chamber and the valves with the piston and i could run 91 octane, we even tried 87 just for fun and it almost handled it..........till it got warm. then not so much, if your running over 12 to 1 comp you dont really have to worry about quench as much, its going to light, quite violently at that

 

When I broke a couple of Manifold Bolts eliminating air leaks on my Seca-900, I had to pull the Head to have the Bolt fragments drilled-out.

While the Head was off, I did an Overhaul so I wouldn't need to take the Head off again, any time soon. I knurled the Valve Guides, put-on new Valve Seals and did quite a nice job Porting and Polishing the whole thing before putting it back on.

I Lapped the Valves in and Polished both the Cumbustion Chamabers and the Piston Crowns.
I brought the aluminum surfaces of the Chamber and Piston Crown all the way out to a mirror finish.
I know I got a Gain in Power out of doing the work.
As big a fellow as I am; I'd have to be very careful about wrenching-it wide open in first or second gear.

The Engine would leap through the Power Band and be right-over at the far end of the tach so fast it was crazy.
Not wanting to have the Bike get-away from me ... I installed a Rev-Limiter to keep the revs just below 10-Grand.

 

I can see where you're coming from. I have seen several instances where Mirrored finish in the combustion chamber did not inhibit carbon build up, furthermore the buildup with more concentrated, creating hot spots. Your experience may have been different.

ANY gains from polishing a chamber are going to so minute that you wouldn't notice with the butt dyno. Most likely decent gains came from the fact that, upon polishing, the porter "un-shrouded" the valves improving flow.

I do, however, believe clean and polished pistons are very happy pistons.

As always I appreciate everyone's input, and the wealth of knowledge on this forum that I just found

 

Circle Track racers say that carbon is "free compression".

Anyone ever have their piston crowns coated ? (reduces heat soak, keeps the heat in the combustion chamber?)( burns excess cash in your wallet).

 

my brother and i will be coating piston tops on the race machines if we have any money left after the winter rebuilds. also, we will be coating the skirts of the pistons with a different coating to handle side load friction.

 

I'm sure much of the Membership is unaware of the technology involved in having Piston Crowns and Skirts Ceramic Coated.

For those of you that do not know about the Ceramic Coating Process and have older Bikes that are beginning to "Get tired" and are starting to "Use" a lot of Oil; investigating in the Coating Process might save your engine and add a few years of service.

Particularly, for Bikes that NEED to have OVER-SIZED Piston which are NO LONGER AVAILABLE through the Dealership or in the aftermarket.

Ceramic Coating of your Pistons might be an OPTION because the Coating can be applied to add 4-Thousandths to the Pistons.
Well within the range of the 2-Thousandths Over Pistons -- Unavailable.

 

for more info.....
Max Power engines