Old aluminum is usually very difficult to weld. Old aluminum cylinder heads have decades of combustion gasses, fuel residue, and the residue of everything that passes through the combustion chamber driven into the metal. When you heat the cylinder head with a TIG torch, all of this junk bubbles up and rises to the metal’s surface and contaminates the weld puddle. Robbie has been TIG welding professionally for some four decades now. He is so good he could weld the crack of an ass. I knew that he could handle this and he did so with flying colors.
We mounted the head on a 5/8-inch-thick Blanchard ground flat steel plate. I had the plate ground flat when I was doing a lot of airflow work for Mazda Speed. We drilled the plate to accept hold-down bolts for this head that coincided with this cylinder head’s head bolts. We ran long bolts through the cylinder head’s head bolt holes and through the plate. We bolted the head to the plate and then carefully torqued down the head to the plate in the standard head gasket torque pattern, center out. The head was heated uniformly and only then did Robbie start welding. Yes, like everything else related to this sort of job, there is a process that you must follow if you expect useful, positive results and a workable product.
With the head back, I started the hard part of shaping the chambers to match the new combustion chamber shape that I had created. There was a lot of aluminum now for me to remove and shape. I had a long way to go to get the welded chambers to match the chamber mold.A digitizer and a 4 or 5 axis CNC Vertical Mill would have been nice at this point. But Santa missed me last Christmas. Though someone did leave me a lump of coal.So, I was going to have to do this the old-fashioned way. All by hand, which is normal, no worries.
As the valve seats were removed when the chambers were welded, it was going to be a while before the new seats would be installed so that I could “CC” the chambers or put the head back on the flow bench to test. I formed the combustion chambers based on the silicone mold that I had made of the epoxy chamber forms. It was invaluable. Photographs are limited and can only reveal so much. I spent a LOT of time carefully forming the chambers. Finally, after a lot of grinding and shaping I was done, for the time being. There is still a good bit of machine shop work to be done with this cylinder head before it is finished and ready to return to the customer. I will do what Chris did and how we did it in Part Two of this Bavarian adventure. Like this part, it will be involved.
There were still additional questions to answer before this project was complete. Were we going to have to weld up the seat pockets to eliminate potential ovality of the seat pockets? Possibly and what about the guide bosses and pockets? We would, of course, machine and re-cut the valve seat pockets to make sure that they actually were round and that all seat pockets were set at a uniform depth.
Years and years of valves pounding against valve seat inserts will distort the valve seat inserts and seat pockets. As I could not visually tell how close the water jacket was to the seat pockets, I wanted to check the thickness of the metal and seat pocket thickness to the water jacket with a sonic depth device. Wonderful tool! Now we knew how deep we could go with this machining part of the operation. That would give us a baseline maximum depth and maximum valve seat pocket diameter so that we would be able to order correct new valve seats.
With the measuring completed, I sent the cylinder head off to my friend Bentzion at CTP to have the head Cryogenically treated. This process stress relieves the cylinder head after the additional stress of welding and age usage. This process also strengthens the head at a very basic molecular level. It makes the parts stronger without making the metal brittle. The parts wear better and last longer. It is a good and worthwhile process with which to treat metal components. I have been using Cryogenics on engines parts for some twenty years now. When done correctly by a competent shop like CTP, the process returns truly marvelous results. It works!
34 comments
GREAT ARTICLE!!! invaluable insight!! thank you!!
Thank you Wes.
The quench in the combustion chamber will be improved as well as the flow quality lending to better mixture distribution in the cylinder. The BSFC should go down and the engine will probably like less timing. This is somewhat reminiscent of the Soft Head porting and combustion chamber modifications that Larry Widmer did in the 80’s.
Thank you Mike.
Yep, or people like Harry Weslake way before that…. Hemi combustion chambers tend to create low compression on smaller displacement engines. Story of my life, as I tend to mess with them in my spare time. You could actually diffuse mixture from outside the quench area if you make small channels running towards the spark plug. if the quench angle is actually quite steep on a 2 valve with the spark plug on the side. Rounding of the quench also helps a bit. But you should only do that if your can maintain a high enough compression ratio. Otherwise compression should always be leading.
Then again: port angle an radius are a lot more important, but also the stuff where it becomes really tricky. Not so much for grinding, but actually changing the angle and port itself without casting a new head.
Funny you should mention that. I used the same technique in building up my Honda Ruckus Scooter. Had the chamber welded up to make a lot of quench and to bring up the compression ratio to over 13:1. Then I added the channels to the plug because I read some white paper about it. This thing ran really hard for a 50cc scooter, it could go 60 mph with my fat ass on it and I could outrun guys with a 125cc GY6 engine swap. Many other people have tried to follow my lead and build a fast 50cc but no one has come close!
Way to go Don!! You are the Professor of porting.
Thanks love, I’ll cook dinner tonight for that.
Don
Great to see you “un-leashed” in your forte!
Good onya Don, RF.
Thank you Fred, Mister Indian!
That takes an impressive amount of knowledge and determination to modify a cylinder head with such a poor overall performance, and see the significant improvement that was displayed here. Sounds like many hours of work and quite a bit of patience were required, as well. Very interesting article, well written and thoroughly descriptive in content.
Such a cool article, the old school art of hot rodding.
Thank you for sharing!
Thank you Miguel for your nice comment. Old is the optimum word in my particular case.
Stay tuned, there is more coming.
Don
Dear Don,
Many thanks for the article about the 2002 cylinder head modifications. It demonstrated an unusual and innovative approach to gas flow. I was particularly impressed by the test facilities that you have on hand to prove your ideas before putting them to trial as is the traditional suck-it-and- see method. It must save a lot of scrap! Also what is impressive is the outside specialist support that you are able to call upon and your patience and dedication to the project. Sadly for me, you are now going way beyond my own capabilities these days.
Best regards
Bill
Thank you Bill. Nice to know that MotoIQ is making it all the way to England
A well written (and entertaining!) article. Folks with this kind of dedication and who make fast engines. It’s all about brains and sweat.
Thank you Kris
Jackson
Congratulations Don you are The Man.
Great article Don! Wish I had known about Replika Machinen when I was driving my 76 2002. To date one of my favorite cars. As a current customer I appreciate your dedication to the art of air flow and the paramount pursuit of perfection!
Thank you Jeromey
Great article. I am actually about to start on a rebuild project with my 2002 (with x60,000 miles). I won’t be able to to this level work certainly! Any recommendations for shops to do more basic head work in the Bay Area?
Thank you for your comment. We can and do, do less involved cylinder head work. Mike asked me to feature this project as it shows what can be accomplished by people with lots of experience in cylinder head and engine work.
Call me and we can discus your project.
Don
Great article Don! You are a wealth of information. On a side note, Don has been working with us on a new cylinder sleeve design. Stay tuned for more on that.
Thanks Jeff, I guess I better call you!
Good job. It is a good article for those that want to learn.
It is unfortunate that most of the readership do not understand how much work it
is to do the work on the parts and test them AND then generate the words to
explain it to them. I hope they pay you for these efforts.
Regards,
HB2
Thank you Harold for your comments and encouragement.
Don
Don, many people believe that a cylinder head is just a lid with holes for the valves; you’ve proved that it is much, much more.
It was a lot of hard work, but what a good job well done.
Eddie.
Coming from a world class restoration expert like you that is high praise.
Hope you are doing well over there.
Thank you, Don
Thank you Billy.
Three positive comments from over “The Pond”. Spanning the Wide World of Air Flow.
Don
I’m really interested in seeing what kind of numbers the little m10 will put down with that kind of flow improvement..
Thank you PJ.
I am only involved with the cylinder head. At this point what, when and where as far as the rest of the engine goes are a mystery.
Don,
what ‘s and arm wavy cost to do this work AND now that you’ve done all this learning would a 2nd head like this one be cheaper?
I think that you are asking about the price to reproduce this cylinder head. Cheaper???
I have been porting 2 and 4 stroke cylinder heads for over 40 years. What is that life experience and knowledge worth?
It has taken a LOT of work to get to the combustion chamber and the CFM to the point that it is currently.
Will additional “copies” of this cylinder head be less expensive than the original? Possibly, that depends upon the demand.
If you are truly interested then you can call me and we can discuss it.
Don Redmon
Replika Maschinen, Inc
831-359-0863