• Honda part numbers incorporate a center section that identifies the model that the part originated on. Most of the parts on a new model were identified in this section as new to that model, of course, but several more common parts would also be identified as originating on previous models, typically oil seals, bolts and other fasteners, a few electrical items, etc. At the time of the GL1000's introduction in 1975, "371" was designated as the GL1000 model code, and many of the bike's part numbers naturally contained this number. Interestingly however, because the auto team drove the project and in fact designed the engine, some of the GL1000's parts have part numbers containing "600" codes instead of "371". This is because Honda at that time reserved numbers 600 and over for their cars and the GL1000 engine contains several Honda car parts.

• Due to the very loose (well over 0.005") fit of the camshafts in their bearings, valve clearance changes dramatically as the camshaft rotates. Perfectly set at TDCC, at 90 degrees (180 on the crankshaft), the clearance will be close to double. Similar to most of Honda's 1970s engines, this is of no consequence, not even excessive noise. And it does not mean the cam lobes are mismanufactured. It's all in the loose fit of the bearings.

• The GL1000 through GL1200 have massive crankshaft flywheels, standard automotive practice and just one of many artifacts of the bike's original automotive heritage. Because of this, you cannot expect the engine, no matter how well tuned, to have anything like the throttle response of say a GSX-R 750.

• Another thing revealing the GL1000's automotive DNA is its "floating" piston pin. Something of a misnomer, this means the piston pin does not rotate in the connecting rod, but only in the piston. In every other Honda motorcycle engine and virtually all other powersports engines the piston pin rotates in both the connecting rod and the piston. A special auto-derived tool is required to remove the pistons because of this.

• A third car attribute of the GL1000 is its carburetors, which were closely copied from those on a very early Honda car. The carburetor castings are nearly identical and many of the parts will interchange.

• The GL1000 ignition system is the most unique and non-intuitive feature of this bike. Far from being as simple as it looks, it takes countless revolutions of the crankshaft and kind of heroic effort to set it even close to correct. It's an extremely fiddly system that extremely few have been able to master. See what I have said elsewhere on this subject.

• Speaking of ignition, the GL1000 ignition coils run on two different voltages. On starting, the coils get full power. Then after, they run on reduced voltage. Seemingly another automotive anachronism, no one is really sure why this was done to the GL1000 and defeating this goofy setup actually yields improved ignition performance, with no durability drawback.

• The GL1000 has ignition points that look like those in the 70s 450 twin. But don't be fooled. They are not the same and using 450 points results in reduced adjustability and despite what many say, no performance advantage.

• Once spied in the text of a European Honda advertisement, it is likely the "GL" model designation came from the words, "Grande Lux", a phrase meaning the pinnacle and which we in the anglo world have irreconcilably and improperly bastardized to, "Grand Deluxe".

• The GL1000 lacks an accelerator pump on its carbset. And it can use one. There are even folks who have managed to fit enough Honda car carburetor parts to give it one. And some fit GL1100 carbs which have an accelerator pump. But there is a much better and easier way to get excellent throttle response in a GL1000. This involves several tuning steps, the most effective of which is adjusting the pilot screws to 3 full turns out from gently seated. This makes the idle a little richer than it should be when checked on an exhaust gas analyzer, but it is worth it for the significantly improved throttle response it and the few other special adjustments (such as the 0.006" valve clearance) deliver.

• Adjusting the valve clearance on this engine to 0.006" instead of the factory recommended 0.004" will increase cylinder compression by a minumum of 10 psi, with no drawbacks and an expected improvement in starting and low-speed performance.

• As with any 50 year old Honda, the GL1000's engine will usually be found to be under-powered due to age and wear. Most of this is due to cylinder wear, though valve and valve seat wear will also be evident. Remachining the cylinders is a bigger job than on other vintage Hondas due to the automotive-like unitized cylinder and crankcase, so very seldom is this needful procedure undertaken.

• The four-cylinder Wings boast four different carburetor sizes. The GL1000 has two different sizes (75-77 versus the smaller 78-79), the GL1100 its own smaller size, and the GL1200 carbs are smaller yet. This is because Honda gradually accepted the fact that the Wing was not a sportbike, despite being promoted as one in the earliest advertising. So little by little the size of the carb bore was reduced to move the powerband lower in the rpm range and make the bikes more suitable for heavy road use.

• There is a significant party of GL1000 single-carb conversion advocates. The truth is that few if any carb conversions go exactly as planned. Carb manufacturers do not make their products easily adapatable to other engines in the sense of tuning parts avaiability and you should know that it can take years to get to anything approaching adequate performance and not many have been satisfied with the outcome. Moreover, the original carburetors once prepared properly work outstanding and proponents of conversions are folks who have been frustrated--due to poor work and/or parts--with their stock carburetors. However, the factory carbs are not difficult to service, they just require a bit more than a "dunk and rinse" rebuild ethic.

• Although for almost twenty years centering around the early 1970s Honda put valves in their powersports engines that were made cheaply and so soft that they receded rapidly, resulting in such a steady loss of cylinder compression that by 15,000 miles 70s Hondas are decidedly below par, the GL1000 was an exception. The GL1000 escaped some of this trouble kind of by accident. Though it has the same soft valves as the other Honda engines of its era, its auto engineers, in specifying unusually (for Honda) soft valve seats, unknowingly gave the GL1000 and GL1100 something of a reprieve from the severe valve recession malady that plagued other models.

• Along with many other vintage Honda models, the GL1000 has the reputation of melting its alternator electrical connector. Though alternator failure is sometimes experienced also, there is no correlation between these two things. Connector failure is due to the very old style open-back electrical connectors which to not seal off dirt and moisture from entering the wiring, and the fact that the wiring is crimped. Once these two things are addressed, the exposed connector by filling with grease and the crimps by soldering, the failures will stop. And, although several aftermarket sources have arisen in recent years, the connectors are available from Honda and always have been.

• The GL1000 starter clutch, the part that connects and disconnects the drive function between the electric starter motor and the engine, has an above-average failure rate. Though not difficult to repair, the engine does have to be removed from the frame and the parts are long discontinued from Honda. Good used parts must be found, which will be a challenge.

• The GL1000's reserve lighting unit is a black box that automatically turned on the other beam when one of the headlight's beams failed. The box itself was prone to failure and Honda actually recommended to its dealers that it be bypassed electrically.

• The neutral light switch in the GL1000 has a history of failure and according to the service manual requires removal of the engine from the frame to replace. Enterprising techs soon discovered that the switch could be replaced in the frame, with a little loosening of engine bolts and prying with levers. Even Honda capitulated and changed the recommended allotment of time in their warranty flat rate manual.

• Eventual head gasket failure on this engine is accepted, with the result coolant ingestion by the engine. Replacement factory head gaskets are now pretty much history and aftermarket ones have proven to be much lower quality and unreliable. One aftermarket company that reproduces the composite style Honda head gasket is Cometic in Ohio. Be sure to coat the head gasket with Gaskacinch as experienced Honda mechanics have done for more than a half-century.

• Sadly, these bikes are not being appreciated on the vintage market as they should be. That combined with their age means many of them are not being loved the way they deserve.

Suggested further reading:
Interesting GL1000 carburetor facts
GL1000 myths
GL1000 ignition anomalies
Twenty-five things you should know