185cc GILFAX MONSTER MOTOR

[Mack]

RK was testing many port configurations at that time, and that was one of them. He almost always ground out the exhaust guide as he obviously knew that there where gains in the exhaust port of these heads (which there is)and also he knew the guide was also going to probably outlive the engine for his intentions at that time. As for the inlet, this has not been left alone trust me. This port has had a lot of work go into it. The downdraft angle of the port has been increased by porting right up into the spring seat area and raising the floor with epoxy. After porting the guide was then inserted to where you can now see. There just is not enough room in the head left to run a shorter guide as he raised the roof so much and is trying to cleanly seat a much bigger than stock valve. Have a look at the piccy again, you can see the top of the spring and valve and how short it is and how little room is left for any guide. If Rk had any room to leave the guide flush then it would have been gone.
The things you are asking about porting tubes are correct. It is standard safe practice to grind the inlet guide out and leave the exhaust guide fairly well alone. On a setup like RK was building you are talking very modified from stock in components and design.

 

[Cactus Jack]

Hi Mack , as for the valve seat inserts ....... alloy expands at a greater rate than steel so it makes sense to machine seat bores in alloy heads so that the inserts are a tight interference fit in them rather than a press fit .........

Then you heat the head in an oven and cool the seats in a fridge before quickly pressing them in (as with new iron cylinder liners into alloy barrels) ........ then when they're both at the same temperature , there's no chance of 'em coming loose or being hammered out .

You need the interference fit to be maintained at and above max operating temperature .

 

[tubes380]

yes that all makes sense now thanks mack, i see how the inlet guide needs to be left alone in rk's head, and i know there has been a lot of work done, was just asking the whats the norm with the guides. i think i will grind my inlet flush and work around the exhaust guide the best i can, thanks again

 

[Mack]

That is what you should do tubes, if you are porting a 140 head you will find that if you are careful and leave it a little raised leading up to the guide you will not break through to the spring seat area. The exhaust guide can be faired off and shortened a little like 3mm or so and deepen the channels either side of the guide and reduce the alloy boss around and leading up to the guide. Then taper the port out to match the exhaust header (including the washer). This will open the exhaust up a lot. Bolt up a 32mm mandrel bent exhaust welded without steps or penetration and you will see a great improvement.

Hey cactus, yeah thats pretty standard for proper seat installation, but I have heard complaints from guys who I presume have done it properly that the seats are still hammering loose. There is a great variation in the rate of expansion and strength among the alloy group and who knows what alloy is in these heads. I was wondering if perhaps rk had trouble seeing as he was pushing the limits so to speak. He was using beurillium seats and was experimenting with aftermarket valve springs for crf450's at that time. I followed most of his builds and he made many changes through that period showing that he wasn't happy yet. But he would never release the exact details of his work or failures (understandably) at best a cryptic riddle with a partial hint contained!

 

[darb110]

NOICE =D hehe
you seem like youve got the cash for it and certainlly got the determination =)
good luck with em all, should be great fun to ride haha =)

 

[rkfinch23]

hey guys.............. i do have a monster head for sale as we speak, i'll put pics up if anyone is interested..

 

[no_crf50_here]

*left eyebrow just raised a touch*