I was fortunate when I started restoring a vintage Model T powered sprint car that the Rajo B head was pretty much complete and original with little or no wear or tear. A rocker arm stand had been cracked and welded and the valve springs had a smaller second spring inside the original Rajo spring. I expect that the cause of the broken rocker arm stand was the result of the increased spring pressure from adding the smaller springs (the cam had about .280 of lift).
I put the head back together without the additional spring and thought nothing of it until I started running the engine. At higher rpm the engine would “cough” back through the carburetor. Consensus was that either a valve was hanging up, or there wasn't enough spring pressure.
The original Rajo springs have a free height of approx. 3.095, an OD of 1.326, ID of 1.062 and a wire size of 0.132. At a closed height of 2.424 (measured over the spring retainer) there was approx. 26 lbs of spring pressure (looking for between 40-60 lbs). Open at 2.049 (stock cam lift @ .250 and 1:1.5 rocker ratio) there was approx. 38 lbs of spring pressure. Needed more spring pressure (actually I removed the springs by hand without the need of a spring compressor).
I studied the SBI catalog religiously hoping to find a close match. If a match was close it was for some off the wall engine that the chances of finding that particular valve were slim to none. Started to look at using a second spring inside the Rajo spring.
Dropped a stock Model T spring (almost same free height as the Rajo spring) inside the Rajo spring and measuring with the spring retainer came up with a closed pressure of 59 lbs and an open pressure of 83 lbs. Sounds good with the exception that on the Rajo head there is a boss that houses the valve stem bushing that the Model T spring would sit on top of, adding some additional pre-load to the T spring value. So to replicate this I used a second valve spring retainer on the bottom (allowing the Model T spring to sit on top of it). Closed pressure was 81 lbs and open was off my scale (100 lb scale).
If the Model T spring had a shorter free height it might work. I cut an 1” from the Model T spring. Using two spring retainers (one on top and the other on the bottom). Closed pressure was 55 lbs, open was 84 lbs.
I intend to use the shortened Model T spring inside the Rajo spring on this engine unless someone convinces me this the wrong thing to do (and can provide an alternative). I'll keep you posted on the progress. Hopefully this can help someone else with a similar problem. Joe
Joe, I don't know about the RAJO springs but all of my Frontenac heads have double springs. MG
Buy one of these kits and take a measurement. The Large spring diameter compared to the original spring I have is near perfect, wire diameter is close, the height is close, and the spring pressure is 1.5x the pressure of original spring I used for comparison. For $13, you can test pair, not be out much if wrong. Cannot tell you how many spring charts I looked at before I stumbled on these. I get you are asking about double springs, but this might be an alternative for you.
Brian do you have a B style Rajo? Reason I ask is that the free height of the Enfield spring is right at 2". This is less than the closed height of my springs. I'm using the original valves and keepers. Thanks
Joe, when you roll it over does the spring bottom out? If it does you will wipe out the cam shaft lobes but if there is clearance I would run them. There is nothing worse than floating valves at high rpm's.
Joe, still some spring length left with the valves open. So if I understand you correctly you see no problem using the Rajo spring with a shortened Model T spring with the 55 lbs closed and 84 lbs open as long as i'm not collapsing the spring? Thanks
Maybe you can fix the floating valve issue with single Rajo springs by the valves and additional weak Model T springs on the pushrods placed like the original Model T sidevalve springs?
Roger not sure I understand? Change the subject slightly I spent a fair amount of time in Stockholm and Linkoping. Loved going to Sweden, where are you located?
Joe, check this thread for more discussion and pictures of extra springs on the push rods placed down in the old valve galley: http://www.mtfca.com/discus/messages/331880/387668.html?1379079811
I'm down south in a small town, Olofstrom, about 200 miles from Linkoping.
In the Musclecar V8 world, extra springs down by the lifters are called a "rev kit".
From the internet re: "rev kit"
"Well the only way an engine looses that much power up top is from valve float; that's caused by inadequate valve spring pressure. The rev kit can help the lifter stay on the cam but can do nothing for the valve. The main reason we run rev kits in race engines comes from the link bar solid roller lifters we use in most applications. When we have a top end valve train failure what tends to happen is the pushrod flies up and out of the way allowing the lifter to come out of its bore. Once it does that the lifter that it's liked to will tend to turn sideways and start destroying the cam, its lifter bore, and run metal throughout the engine until the driver gets it shut down. With the rev kit, the lifter on the problem side should stay in its bore and keep damage to a minimum.... With a factory roller block you have already eliminated this threat..."
Read more: http://www.corvetteforum.com/forums/engine-mods/1878648-what-s-the-story-on-thes e-rev-kits.html#ixzz459bqTpUd
Sure, the spring on the pushrod will only help control the weight of the lifter and the pushrod - but that's at least half the weight of the valve train and the sole spring on the valve will have an easier job keeping itself and the rocker in contact with the camshaft's impulses. Cheap & easy to install with just a hole in the pushrod and Model T parts, easy to take off if it doesn't help & special double springs are necessary.