I got this rajo head in a trade. It appears to have been cast with oblong cylinders for use with pop up pistons. Everything is machined except for the spark plug holes and the valve seats. I think I'm going to have hardened valve seats put in, and have it drilled for 18mm spark plugs. My question is, should I machine the cylinders back to round, or leave it how it was intended? Any other advice?
I looked over that head at Bakersfield last year. It's from the Signal hill days. If you look closely at the combustion chambers, you'll see a material color change where the chambers are oblong. That head started life like any other B RAJO. Since then, it's been welded, decked, and the chambers cleaned up... And never finished.
Not a bad start for someone lookin for a high compression, go fast head
You would need to run a zero deck piston and you would end up with a lot of compression. You should measure the chamber and do the math. Swept volume plus chamber divided by chamber volume. If over 8:1 you have a hard time running any timing.
Should I mill it back to round?
No, why? Just check how much volume you've got in the combustion chambers and we'll figure out your new compression ratio.
They could just run about 4:1 compression ratio back then due to bad gasoline, while the engine gives more power with less heat for every ounce of gasoline with higher compression. The limit for compression in a T is the babbitt bearings - about 6:1 is considered as a practical limit for splash oiled engines. With pressure oil and insert bearings you can go higher, though the combustion chamber shape sets a limit - but that's more for flatheads that'll get bad flow above 9:1.
I don't think it's even necessary with hardened valve seats if you're going to run this Rajo on the street - you'll rarely touch 3000 rpm, more like below 2000 on the road, while the problem with valve seat erosion without leaded gas appears mostly at 3000 rpm and above.
Absolutely no reason to put hard seats in that head unless you run into weld porosity in the seat area. Machine the seats and put a good valve job right on the cast iron and run it. Don't go nuts with big boy seat pressure- no need for that at all- even with 3000 rpm. Just saying. Dan
Agree with Dan on the hard seats and spring pressure unless you plan to build a lot of HP and RPM.
CC the head and do the math. Don't think you would have a problem with to high of CR with flat top pistons but what ever you do you will be having pistons made to your spec. I wouldn't worry to much about timing over 8 to 1, you just have to know what your doing.
Just depends on what you want to build, go fast will not live as long and a good runner.
The engine in my hill climber will not last 500 miles, it's all about launch and 520 feet to 1/8 mile.
I have 4x.030" used but in good condition flat top aluminium pistons I took out of a T block. They would be a good combo for your head if using stock stroke/rod & crank.
Frank I'll PM you about those, I'm very interested