Porting!

[noidea]

yea, im going to get them redone.

Thats what i was saying about the port. Its been opened up heaps by some sort of milling machine. Its alot bigger than the intake manifold... I might take the head off my bike and see if its port is a bit smaller.

The area im talking about is the red area. I marked the port with a red texta and then ground it on the same angle as the inside of the seat. You can see the corner isnt smooth, the valve seat is smaller than the corner of the port and so there is sort of a lip there.

ive changed ur diagram a bit, the lip im talking about is this, http://www.mypicpal.com/jarvie/My%20...s/untitled.JPG

I think ill take a bit more off the sides of the lump infront of the guide and also a little more on the very top of it, thats if i continue with this head. Yea its a ducar.

edit for link to pic.

[Mack]

Oh, ok I see what you've got there. It is not ideal that the bowl area before the seat ring has a big scoop out of it. Nor that the port opening is so damn huge. I have seen this on Ducars. The ports have been ruined by the factory. Basically they have not left you anything to work with. There are three options open to you if you want to persist with this head.

The first is ignore the problems and do the best you can to clean up without enlarging.

The second is to install a larger seat and valve. That way you will reclaim some workable material and be able to rectify the bowl area and be able to shape the port to a preferred shape. This will mean though following up with a big bore kit and cam and bigger carby to make the whole thing work. This is exactly what is done with the big hp motors. It is the best option as far as power goes, just know that it is a very committed path in money and time.

Or number three, you can use a filler to reduce the oversize areas and shape to your liking. This way you can improve the flow and stick with stock valving and carb if you want to. The easiest way to do this is with JB weld. All you have to do is clean the port surface up like you have already done. Then drill with a tiny drill a few holding holes into the areas you want to fill being carefull you have meat behind those spots. Then gouge the entire surface to be JB welded with your alu cutter. It is then just a matter of mixing it up and building it up all through the areas you want. It can then be sanded to any shape you want.

[noidea]

Yea... sounds like this head isnt really a good base to start with then. I might leave it as is and possibly save it for a big hp motor or something. When i finish my exam today ill have a look at the head on my loncin and see if its better. I would imagine that head would perform better than a stock head, might give it to one of my mates or something.

cheers and ill let you know how i go.

EDIT:
Took the manifold off my loncin engine today. The head is untouched, looks like i will be taking it off tonight/next moment i get spare. Ive been looking at the pics of ur ports and i cant see the squished oval or D shape your talking about. Seeming as ive got a bit more meat to work with on this head i might try for a good port shape. Can you fill me in a bit about this process.

thanks heaps for your help so far man

Edward

[Mack]

While you've come this far with the ducar head you may as well grind that guide down a fair way before you put it back together. You have to make sure you have no burrs in the mouth of the guide too before re-inserting the valves. Also once done porting fill your laundry tub with hot soapy water and clean the head thoroughly with a toothbrush and force water through every passage. Also clean down the guides with cotton bud. Then dry with compressed air (or hair dryer if no compressor). Make sure you inspect in every cranny for crap. Then thoroughly oil everything with fresh oil as you put all the top end back together.

As far as shape goes you just have to look down into the port at the shape of the port at the far end. If you look at before and after shots you can see the differences.

[noidea]

well, after comparing them, i think your JB weld idea is going to be the better one.
Except that it seems the head volume of my loncin is ALOT more than the ducar head. But im thinking the valve sizes and port sizes will make up for the loss in compression... but now im going to have to think about a high compression piston... Heres a comparison of valves an ports:

Ducar head -Intake- Valve: 27mm
Inside Seat: 23mm
Manifold end of port: 29mm
Manifold: 22mm

-Exhaust- Valve: 22mm
Seat: 20mm
Pipe end: 24mm

Loncin Head -Intake- Valve: 23mm
Seat: 19mm
Manifold end: 21mm
Manifold: 24mm

-Exhaust- Valve: 20mm
Seat: 17mm
Pipe end: 20mm

So the ducar has a 4mm bigger valve and seat than the loncin. But the opening to the port is a bit too big, and there is that little lip just before teh valve. But that lip is even bigger on the loncin coz of the tiny seat.

The ducar also has a 2mm larger exhaust valve and 3mm larger seat than the loncin. I have also done about 1/2 the porting work on the ducar. How ever the loncin head has alot of metal to play with in its ports, but there is about a 2mm step from the port surface to the seat.

But the ducar has a higher head volume and therefore will give the engine less compression as opposed to the loncin head. but i think overall the gains in port and valve size with the ducar will outweigh the loss in compression which i will eventually regain with a high comp piston or machineing of stock head and barrel.

I think i will stick with the ducar, go and get some of that JB weld and close up the port a little and reshape it to a good size to suit the manifold.

Is there anything im missing with these small valve heads that might be better than the ducar?

[noidea]

hey mack,
found that cam grinding outfit for you.

http://www.tighecams.com.au/bikes.htm

[SIK50]

After reading this thread in its all ive decided we should start a new one dedicated to MACK the ledgend.............. all your information is so good ......... thanks for the help and thoughts

[Bones]

this is without a doubt one of the most informative threads i have read in a LONGG time. excellent posting by both of you on this subject and i second your thoughts on having this as a sticky. great work gentlemen, keep it up.

Cheers, Tony.

[rkfinch23]

very good thread............ let me know if you start another thread as i'd like to share a few things........

[PICCOLO]

well done boys love your work hey mack lol how much 4 you to do that to my head???