MTFCA Forum

I an resurrecting my Rajo BB and converting it to the dual plug set-up. I have a proper Mag on its way with an impulse and I am working through some of the build issues. I am stuck on the exhaust manifold down pipe interfering with the spark plug for #3 cylinder. I am working on spacing it away from the head to gain enough clearance to allow for a right angle plug connection but it is still too close. any flange to adapt to the manifold will come in contact with the plug connection or be too close and melt due to heat. Before I go and build a custom exhaust manifold has anyone done something like this before and have a solution?

I used a short sparkplug I got at the Lawnmower shop ! (don't laugh!)

Thank you for the tip! I looked online last night for a short plug and got nowhere. Did you space your manifold out also?

I have never had a overhead set up so this may sound dumb but can you turn the manifold over & put a elbow on it to point the exhaust down?
All of the pics I found of that exhaust manifold do not have plugs on that side. It's a 8 plug head? Can you run it on 7 plugs? a Harley-Davidson
crank case timing plug I think is the same thread size? The plug Pete referred to is like a Champion Cj8Y or CHA 8481.
Craig.

I'm running a BB w/dual plugs BUT I also made a header. Perhaps with some creativity, you could turn the manifold UP and build accordingly ?

Craig Leach wrote: ↑

Tue Jan 09, 2024 11:32 am

I have never had a overhead set up so this may sound dumb but can you turn the manifold over & put a elbow on it to point the exhaust down?
All of the pics I found of that exhaust manifold do not have plugs on that side. It's a 8 plug head? Can you run it on 7 plugs? a Harley-Davidson
crank case timing plug I think is the same thread size? The plug Pete referred to is like a Champion Cj8Y or CHA 8481.
Craig.

MOST overhead valve heads for model Ts are four spark plug setups, including the Rajo model B. Most have the single set of spark plugs on the best accessible side, which varies with maker and models. However, the model BB (note the model difference) Rajo is an eight spark plug arrangement with one set on each side to run a dual ignition if desired. Many BB owners run them as single ignition with a plug in the spark plug hole, usually on the left side due to interferrence from the exhaust manifold and heat issues.

pete eastwood wrote: ↑

Tue Jan 09, 2024 10:35 am

I used a short sparkplug I got at the Lawnmower shop ! (don't laugh!)

I am not laughing. I have heard of several people doing something similar with a really small spark plug on the one location, and was going to suggest that myself (but you beat me to it!).

The BB head came from the factory with dual plugs. 18MM on both sides. If you have pipe thread plugs on the right it is a model B that has been drilled for dual plugs, not a BB and will have a lower compression ratio. The BB is a top end high performance head and was never intended to run with the cast iron manifold. It was assumed the user would be running some kind of headers or racing pipes which would not interfere with the plugs on the left side.