Oil Pressure, Carb, Saving Paint and Chrome Q and A

"An old rule of thumb for oil pressure is 10lb per 1,00rpm"

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Oil pressure issues

Q: Hi Keith. I have an oil pressure issue. I took a 1974 Triumph T160 engine and had it rebuilt with the only changes being new Amal carbs, new clutch, new 3-into-1 exhaust, new camshafts and lifters, Boyer ignition, new pistons and bearings and rings and a new high pressure oil pump. The bike runs fine for the first few miles then as you slow down to an idle to stop the oil pressure drops to zero. Add a little rpm above idle and it climbs back to a normal pressure (about 20lb) then reaches 40lb while running highway speed. The engine is mounted in a Trackmaster oil-in-frame unit. I read somewhere that the Triumphs factory-made with these oil tank in frames had similar scavenging issues. What is my oil pressure problem? How do I solve it? Thank you for your time.
Rick Rahm/via email

A: My 1974 Triumph T150 behaves similarly when the oil is hot. At idle the gauge drops to nil, but blip the throttle and it climbs instantly. An old rule of thumb for oil pressure is 10lb per 1,000rpm, so while 40lb at 4,000rpm may seem low, it’s not a disaster. Another test is how long it takes for the low pressure light to come on after you kill the engine with the kill switch. If it comes on instantly you most likely have a problem with the rod main bearings leaking out too fast. Another possibility that I just faced was the condition of my oil pressure gauge. The plastic face was crazed from sun exposure and it started weeping the fluid used to dampen the needle. I replaced it and the new gauge shows better readings at all rpms.

Carburetion question

Q: I have a 1978 Suzuki GS1000C that I am bringing back to life after many years of it being stored in my late Dad’s shed. I have had a lot of work done to the carbs and engine, and it all seemed to be running OK until recently. The problem is that when I shut off the throttle, the engine revs increase before dying down. This happens when I blip the throttle, rev up from idle, or while changing up/down through the gears. Looking at the plugs, they seem to indicate the machine is running rich, but I was told this problem is one of the engine running lean. Any tips on what to go look at?
Phil Breden/via email

A: That behavior is usually an indication of main jets that are too small. They are running with insufficient fuel and when you close the throttle the fuel/air balance briefly improves. I’d go back through the carbs to make sure they were in factory specifications, and would give careful scrutiny to any replacement jets that were used. In particular, main jets don’t really wear out, so given the choice between factory mains and replacement mains, I’d choose factory.

Saving paint

Q: I have a 1974 Yamaha RD350 that has a couple of shallow dings in the tank and a couple of shallow scratches in the paint of the tank. Keeping in mind that “It’s only original once,” should I have the tank repainted and new decals applied, or would the repaint lessen the value of the cycle instead of increasing it? I feel you would have a handle on an issue like this. I really enjoy the magazine, especially articles on the not-so-rare classics. Keep up the good work. Thank you!
Gary/via email

A: This is a question I have direct recent experience with, and of course an opinion to share. My 1974 Triumph Trident slowly fell out of its wheel chock and leaned into my Norton. The Norton took it well, but the Trident suffered a dented tank. I’m firmly in the “only original once” camp so I searched for a paintless dent repair shop to fix the tank. The result is not perfect but to me is preferable to repainting. You should price out a similar fix and maybe put new decals on. I really like the look of a bike that’s wearing its years with pride.

Slipping wrenches

Q: I truly enjoy your column. For us the younger generation with not much experience the information that you share is truly invaluable. Keep up the good work! I recently bought a 2021 Moto Guzzi V7 Special. I have had several modern motorcycles but not one with this amount of chrome on it. I am mostly used to hex types of wrenches, so this bike is a new chapter in my learning curve. Can you share some tricks on who to avoid marring the chrome on these type of fittings (i.e. mirrors, lock nuts, etc.)? I tried to isolate the fitting from the wrench using a rag and also a piece of leather, but the adjustable wrench keeps slipping. Again thanks for sharing with us your expertise and knowledge!
J.L. Serrano/via email

A: The first thing you’ve got to do is keep that adjustable wrench as far as possible from the bike. Get a set of metric combination wrenches, box and open, and use them. A metric socket set is also desirable. As for the chrome plating, electrical tape around the nut may help slow down the marring, but some is inevitable. Good fitting wrenches will help.

Email questions and feedback to keithsgarage@motorcycleclassics.com or write:
Keith’s Garage, Motorcycle Classics, 1503 SW 42nd St., Topeka, KS 66609

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