MTFCA Forum

I just laid my hands on the Rajo head I bought a while back. It has been in California and I have been in Alaska. It has the rockers, 7 of the 8 original push rods, and the original valve cover. It has been magnafluxed which found no cracks. From what I can see and have read, it appears to be a 26-27 head with the sloped back. It also has both banks of plugs drilled, but they appear to be the same size.

What it is lacking are the springs and keepers and all but three of the valves. In any case, the valves I have are rusty two piece ones I would not want to run. The head is going off to Larry Ofria at Valley Head Service in Northridge to be worked over and put back into running condition. I am wondering about what valve springs people are using on their Rajos.

With two sets of plugs it sounds like it is a "BB" head? I'll check the springs in the BBR head that I have and reply by tomorrow.

Thanks. I don’t have enough to absolutely identify it. I don’t have any plugs here with which to confirm the thread dies snd I know lots of Bs have been drilled. The deck (at least the parts where I can get into the water jacket) are pretty thick so it does not appear to have been planed down. I have read someone stating that 26-27 B heads are rare (36-27 BB heads are more common), but I don’t know if that’s true. It’s marked “B” in the casting and it has the heater outlet, which I think makes it a B. But, I am no expert on these. This is the first one I have had the opportunity to get my hands on.

For valve springs , about 50 lbs. of seat pressure is all you need with this head.

Spark plugs should either be 1/2" pipe or 7/8" SAE. I've only seen one other slant-back B in 40 years !

I have some "old" TRW & NAPA valve train numbers from when I built up my BB near 30 years ago - might be able to cross reference them - I'll get them out of the shop - I have them posted on an old bulletin board !

Here's what I used on mine Morgan - I can't verify if they're still available !

Deleted- hit the wrong button.

Thanks Mark. If anyone would know, it would be you…

Actually, it is the newer manufacture spring Steve mentioned above.

Thanks, his link would not open for me.

Sorry Morgan - I'm technically challenged !

This should help with the spring Mark posted above:

https://www.tractorpartsasap.com/valve- ... 28580.html

Reno Speedster: These original valve springs, the retainer and the locks are from this pre-26 BBR head. It had an inner set of spring/dampers fitted by someone else back in the period when it was raced.

The free length of the standard springs is 3.125" and the wire size is .132."

The serial # starts with an R prefix. Do any Rajo experts know if the R denotes Rajo or race?



If you don't have the original Rajo valves and keepers and retainers, the installed height of the valve spring should be 1.900" measured where the snap gauge is placed in the photo. The spring seats on these heads were never machined flat and are a quite bumpy and rough surface. Since valve springs normally get hotter than the head I face this surface smooth and flat - all 8 to the same height in a vertical milling machine. This gives full contact to the bottom of the spring and the head that results in improved heat transfer and the springs run cooler and hold their initial pressure for a longer period of time. Have your head rebuilder use spring shims here to keep the original installed height.

Don't use a spring with a higher than 45 to 55 lbs pressure at the installed height if you are using a standard diameter T cam because it will add more twist and torsional vibration to it and affect the valve timing.

PS: Does anyone have BBR head they can measure the combustion chamber depth, or know that dimension?



This last photo shows where the original intake side spark plug holes were drilled and the thickness between the bottom of the head recess surface on this unmilled BBR head.

Thanks for the information David. I have read a lot of things on the Rajos, but there is not a lot of solid information (measurements, markings, etc) to aid in identifying what you have or to support/guide a rebuild. I have spoken to a number of folks who have them who have provided information, but still it’s a bit thin.

Did you get the pdf to open Morgan ? It has the springs, keepers, retainers, etc. - pretty much all that's needed to do your head.

Yes, I did. Thanks a ton. I have had a crazy couple of days dealing with the break-in at my ranch and just got it downloaded.

By the way, the one I got is sn 1223x, so a bit later than yours. The back of the head is a bit sloped and a bit uneven so I think (based on what I have read) it’s a 26-27 head. I will compare your pictures of the plug area with my head when I get back to it, but from what I recall, it’s pretty similar.

Reno Speedster wrote: ↑

Sun Feb 13, 2022 10:40 pm

Thanks for the information David. I have read a lot of things on the Rajos, but there is not a lot of solid information (measurements, markings, etc) to aid in identifying what you have or to support/guide a rebuild. I have spoken to a number of folks who have them who have provided information, but still it’s a bit thin.

You are welcome, I don't think it has been, but I'm trying to determine if my BBR has been milled. When you get a chance can you measure the combustion chamber depth on you head?.

I will post some pictures and measurements when I get back to the head.

Well, when I got back, the head was all packed up and ready to send off to the machine shop so I didn’t get a chance to photograph it. It got shipped off to Valley Head Service in Northridge today. I was surprised to find that it weighed 82 lbs packed (more than the block!). Glad I was only shipping it from Sacramento. I might have had to mortgage the house sending it from Anchorage. Fortunately, it will be coming back via a freight forwarder in Seattle, so it won’t be that expensive.

At the cost of everything going up, you may what to prepay the return freight! LOL, Forever Freight!!!!!


Hank

I talked to the shop today and they said the head looks good (no cracks). The valve seats are worn and they (tentatively) think installing seat inserts would be a good idea for longevity and to deal with modern gas. They also recommend using a valve with a thinner shaft to decrease weight. It might also be worth installing slightly smaller valves if this means that a more common valve could be used. It would also reduce valve weight. Anyone have experience with these issues in a RAJO?

This shop works on a lot of old stuff, but their primary business is racing. So, I have to keep them on the preservation rather than improvement track. He was flabbergasted that the recommended valve spring tension was so low. I had to point out it was roughly double what the stock spring pressure was in a T.

All out, high rpm racing, you want the biggest intake head. Back then, they made both valves the same. Today we know with vacuum V/S pressure(I/E) The exhaust valve can be smaller with no performance loss. If you are building a street machine, the largest intake valve may not be optimal. It may not perform well in low to moderate rpms. Like over carburating. Bigger isnt always better.

An update on the head. I just got this photo from the shop showing the progress. Half of one valve seat needed to be welded (you can tell which one on the picture from the polishing/grinding marks. They took a little more off the deck than is shown in this picture (a total of 10/1000).

The goal was to do as little to it as possible, consistent with good running. This was done in order to leave options open for future work if needed. We used the John Deere valve springs recommended, but are a little smaller in diameter than the stock ones. They are a useable spring pressure, running between 50 and 52 pounds.

Looking forward to getting it back so I can start fooling around with it.

A better shot with the deck done and the valves in. Can’t wait to get it back.