WL Compression Readings/Power

[RvP]

We were comparing compression gauge readings on 45s and I have not seen any published data to know what is good and what is bad. My WLA with #5 aluminum heads reads 60 pounds on the rear cylinder, 30 on the front and this caused me to look further and found leaky valves. A friend with a Servi-Car with a fresh rebuild that has about 2,000 miles read 60 pounds in the rear cylinder (front cylinder can not be easily measured without removing the gas tanks). The Servi-Car has iron heads.

I once read that 90 to 100 pounds is the norm, even for old flathead car engines. What reading should one expect on a medium compression flathead 45?

Next question, I never read anywhere the power increase between the medium compression head and the high compression head. Given the medium compression head gives 22/25 horsepower, what will the high compression head give?

[Ohio-Rider]

I’m not sure what the optimum compression should be either for these old flatheads. But for comparisons sake here is what I got last week before removing the #5 heads from my 45” for the purpose of replacing obvious head gasket leaks, my compression test results where, 60 for the front and 80 for the rear cylinder. When testing, both cylinders registered about ½ of the final results on the first kick. Once I get it back together I’ll post the new results -Steve

[RvP]

Indestructible Engine

Thanks for the reply Steve. I am anxious to know what you get when you replace your head gaskets. Due to other obligations I will not be putting mine back in running shape until next week or so.

Just one interesting foot note to my engine. I live in Southern New Jersey and my 45 is a regular rider, about 5,000 miles/year. I ride 2 up on mostly flat ground. I never noticed a problem and could easily maintain 55MPH two up with just a slight throttle opening. It wasn’t until I went to the meet in Oley Pennsylvania I noticed the motorcycle was struggling to climb hills with just me on it. Some hills that did not appear real steep had me drop into 2nd gear and barely cresting at 40MPH wide open throttle.

A compression test in the rear cylinder (60 pounds) followed by an air compressor test using a fitting in the spark plug hole revealed massive air coming out the carburetor when both the intake and exhaust valves were closed (a feeler gauge was passed between the tappet and the valve to make sure they were closed). I could not test the front cylinder until I removed the gas tank and that’s when I found the front cylinder at 30 pounds.

Pulling the rear head revealed a carbon deposit under the rear intake valve that was preventing the intake valve from seating. Pulling the front head revealed that the exhaust valve probably had not hit the seat in the last 500 miles or so. There was not a shiny spot to be found on the valve efface or the valve seat.

Further examination of both cylinders revealed valve springs so weak I could rotate all the valves on their seat by hand. All the valve guides were worn so bad the valves could easily wobble 1/16” in any direction and the rear exhaust valve guide was loose in the cylinder.

I have new barrels, pistons, valves, etc. I am going to put on when I get time in the next few weeks. Had it not been for a trip to the hilly part of Pennsylvania I would never have suspected anything was that drastically wrong. The bike always starts with the first ignition on kick (hot or cold), idles decently and pulls good enough to cruise 2 up at 55MPH without struggling. I have heard that these 45 flatheads are almost indestructible and this is testament to that.

[Ohio-Rider]

Yeah… What they lack in horsepower they make up for in dependability. Last summer I taught my youngest daughter who is 15 to ride mine. She wasn’t allowed on the road with it, but could ride it around the property any time she liked. She learned pretty fast but did her share of racing the engine while learning how to use the clutch. I’m pretty sure that was a contributing factor of the head gaskets going bad. And just like her old man she quickly developed a love for speed, so I’m sure it got over heated a few times as well. They certainly can take a beating. I can’t wait to get the time to put mine back together and whoop on it some more. -Steve