Re: need info on 1950 tn-27 5 hp
Welcome Eric. I have the very same motor (note the avatar). I had to admit I was no expert and not qualified to work on it, so I took it to an expert and learned a few things about them. I am due to get it back after a 1-year restoration.
Rebuilding the carb is the least of your worries on that motor. Sometimes strange running characteristics are more to do with excessive leakdown of crankcase pressure (NOT cylinder pressure, but actual crankcase pressure). You have the last model of Johnson to use the rotary valve system rather than the reed valve system. The bearings on those motors (and generally all pre-1964 under 10 horse) used cast-in bronze bushings as bearings in the main web of the engine block. They were strong and well suited to the task of which they were asked. The problems are that they were not intended to last forever, so when excessive clearance between the crank journals and the bronze bushings (bearings) occurs they are cast in, not replaceable inserts. You cannot grind the crank journals smooth and then compensate by using oversize bearing insert (there are no inserts). On a rotary valve motor especially, the pre-combustion pressurization in the crankcase is important in the combustion cycle. It compresses the intake mixture and then, under pressure when the intake port is exposed, shoots the mixture into the combustion chamber (deflected by the piston deflector). The trouble is while one cylinder is in compression the other is in vacuum. If you have leakage through excessive bearing / crank journal clearance it mucks up the whole affair, losing pressure where you need it and bleeding it into a chamber that needs vacuum. It mucks up the whole cycle and leads to strange operating characteristics. The rebuild manuals tell you how to deal with it: ?replace the block and crank.? Like you can just rush out and do that on a motor that went out of production after 1953. I had to get my block and crank replaced with a 1952 TN-27/28 assembly with proper clearance. I consider myself lucky to have employed the services of a restoration shop (nymarine.ca) that knew all about it. Ever the glutton for punishment I decided to go out and buy a 1958 Johnson 7? that uses the bronze bushings (at least it is a reed valve and not as profoundly affected by excessive clearance and pressure bleeding). That motor I am going to attempt on my own. I know it was a runner when I bought it.
The TN (1950-1953 with neutral) & TD (1941-1949 pre-neutral) motors were great trolling motors when all is right with them. Considering how old they are it is quite telling how many you can still find in service. Sooner or later it is time to call in the lease on life. Hopefully yours is not excessively clearanced in the bearings. For what it?s worth if it is the case, hard chroming (not the fancy, shiny chrome) can be applied to the crank journals, then be turned down for proper clearance with the bronze bushings (bearings). The motor certainly ceases to be a cheap project at that point and becomes an obsession. It can be done, but no sane person (or person with funds through normal channels) would attempt such a restoration. Colour me insane. Good luck and please keep us posted. Inquiring minds want to know!
PS. Please make sure you run TCW-3 oil at at least a 24:1 ratio if your bearings mean anything to you. Bronze-bushed motors demand it!
ive cleaned the milky white fuel tank and the petcock on the bottom but need help with the carb end of it. will get new carb gaskets soon. any help is greatly appreciated.
