Porting an early 80’s 430

I decided to attempt to change the ports on my 430 before the next race at Perris on June 6th with CalVMX. The port work is based on information I received here in answer to a previous post. (Porting Advise for a early 80’s 430) I would like to again say thanks for the service bulletin information. I would not have attempted this without it. I did not take any before photos (sorry) and I did not perform all the service bulletin modifications for reasons stated later.

The first modification called for adjusting the exhaust port to 39mm (CR/XC) or 40mm (WR) from the top of the liner. On disassembly and measurement, I found mine to be 38.96mm and I concluded no adjustment was required.

The second modification was to square the rear corners of the side transfers. I am not a big fan of shape corners on ports for reliability reasons. I think they can cause ring wear and damage, so… because the change in port area was very small and there was no change in port angle, I decided not to pursue this modification. (I believe it reasonable to conclude there would be little performance penalty for doing so.)

The third modification was to raise the piston port window by 4.5 mm. This is based on a stock single ring piston. Unfortunately I am running a Wiesco two ring piston and 4.5mm will place the port window into the lower ring groove. I raised my piston port window by 2.25 mm. I thought that was the prudent limit. (See photo)

The fourth modification was to reshape the rear boost ports into what I would call an eyebrow configuration. This modification definitely adds a good deal of port area and changes the rear flow pattern as well. The pictures show the modified ports viewed from top and bottom.

The fifth modification was to add 30mm to the expansion chamber where it passes the front tube. This modification was applicable to the WR only. I have a CR pipe and did not pursue.

The final modification is to change to a Mossbarger reed valve assembly. I have one.

Along with the above, I also matched the transition from the reed block to the cylinder, added some epoxy to blend the transition from the aluminum to the liner on the side transfers and did some general smoothing of the port castings. I have previously matched the case to cylinder transitions.

I still need to reassemble and get the jetting dialed in which I am hoping to accomplish at the track this weekend. I may try some variations in ignition timing to find the best compromise if time allows.

Regards,
PC

Holy Cr_p!

Well, it is back together and with a shocking degree of new grunt and throttle response! Wow and I still haven't played with the jetting and timing yet. I am headed out to Perris on Thursday evening for some practice and to dial it in. I have yet to wind it up all the way, but the bottom and midrange are very powerful. I can break the rear wheel loose on the pavement in second gear with a twist of the throttle. A very different personality. You can't sit far enough forward. This IS what I was hoping for. Thanks again.

Huskydoggg-
My 430 is a composite. The frame is from a CR. The motor from an XC. The only difference that I am aware of is the XC uses a wide ratio transmission. I am using the stock external flywheel Motoplat ignition. My squish clearances worked out to be .041" at the front and .054" at the rear of the piston. I am using a .017" thick cylinder base gasket. I don't know why the difference front to rear is there, I suspect it is just a 1981 Husqvarna manufacturing tolerance

Regards,
PC

That sounds great all the way around. Now, about that squish distance...

The piston rocks quite a bit front to back, and my best guess is that's why there's a difference in squish. Usually, it's measured parallel to the wrist pin for this very reason. I would really like to hear what you get measured this way. Also, is that a stock metal-mesh base gasket? If not, where did you get it?

I smashed some more solder for the side to side measurement and came up with .047" on the right and .0465" on the left. I measured front to back originally because that is how my book (Two stroke performance tuning by A. Graham Bell) states to do it. I also have Eric Gorr's book, but it is silent on position of the solder during measurement. None the less, I couldn't help but notice that the side to side measurement is numerically centered on the front to back measurement. Hmmm.
I cut my own cylinder base gasket from materials purchased at Pep Boys. It is what I would describe as oil paper gasketing (Gold/tan color) and I used Permatex, Aviation Form-a-gasket liquid as a dressing.
I chose to make a thin gasket based on A. Graham Bell's writing, seeking to set my squish clearance near the minimum he states for a big bore motor. There are some advantages to doing so. I am also aware that it will change my port timing slightly, biasing it toward low end power. I have measured the stock mesh style gasket previously at .052"

Regards,
PC

Thanks for the follow up. I thought that was quite a bit thinner than a stock base gasket.

Those are some good squish measurements there! But I'm surprise to hear that somebody who wrote a book recommended front-to-back measurements! I sure wish we had readily available gaskets in a bunch of different thicknesses, ala KTM. The stock 430 motor varied a lot in final cylinder/port height/squish and some run hard... and some don't! It's worth taking the time to get right, wouldn't you say from your experience?

PC- no excuses for not hole-shoting & leading at Perris! C U Saturday

brrraaap!

Race day

Well, I went to the race on Saturday and after some final jetting adjustments, I have this to report. The bike worked very well indeed. It was sharp in the low end with a solid mid-range hit, the top end was unchanged from what I could tell. I placed 2nd for intermediates in the bike class and finished 2nd in the plus 50 intermediates (age group) in moto1. Unfortunately, I grenaded the transmission in moto 2 and that put an end to my night. Don't feel sorry for me, because I am very pleased with the bike in general and the top end in particular. I have been through 3 bottoms in 7 years and was about due on this trans. I have collected boxes of spares over the years to support my racing delusions, including a CR tranny that I have been waiting to install. So life is good, all I need is 3 gaskets, a spare weekend and I'll be ready for the next race.

Cheers,
PC

Huskydoggg
I am glad you are happy with the porting. It was for me the single best modification I performed to my 430 and I am very happy with it. It is the difference between adequate off-road performance and a race machine. I believe anyone armed with the service bulletin, some basic skill, a die grinder with assorted bits and a little attention to detail can do this with good results. The bit that worked the best for me was an inverse Christmas tree type, skinny at the shaft and wide at the top.

Regards,
PC