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15 Minute Oil Mod

So, what's an oil mod, and why does my bike need one?

The major design problem with the early-80's Honda V4 engines was early cam and follower failure (here's one site that details V4 cam history). While several factors contributed to this damage, the key element was insufficient oil flow to the heads. Several modifications were developed to correct this problem, both by the factory and individual riders.

On some of these bikes the cams failed very early (less than 20,000 miles) while others have run over 100,000 miles with no cam problems. My bike has over 46,000 miles and the last time the valves were adjusted (at 40,000 miles) things looked fine, so mine may be one of the bikes that doesn't have a problem. But I'd still like to do all I can to keep it running to 100,000+ miles, so I decided to do an oil mod.

The original cam lubrication design took oil from the transmission and routed it to the heads through external lines. These lines ran from the transmission to the heads on the left side of the engine. There turned out to be three problems with this approach:

Insufficient oil flow to the heads caused by low oil pressure at the transmission port (the transmission gets less than full system pressure),
The transmission's oil is unfiltered, and
When the engine is shut off the oil drains out of the metal lines. When the engine is next started the cams get no oil flow for some time. On some bikes, no oil flows to the heads at all when the engine is idling.

To correct these problems several modifications were developed. The first type involves drilling into the main oil galley and routing filtered high pressure oil to the heads through hydraulic hose. While certainly effective, this is a pretty invasive procedure. You drill and tap the block after removing the right engine cover, and pull the radiator or carbs to attach the hoses to the heads. It does work; here's a site which compares a stock system's performance with a modified system.

Since I was looking for a bolt-on, non-invasive approach, I kept looking. Here's a site that describes an adapter that mounts between the engine and the oil filter, giving access to high-pressure, filtered oil. And since the filter has a check valve, oil is trapped in the lines so it gets to the head quicker on startup. This sounded much better to me than drilling into the engine!

The remaining problem was finding an easy way to get this filtered, high pressure oil to the heads. One type of oil mod uses the existing oil lines by connecting the supply hose to the transmission port. I combined the adapter with the transmission port connection into a quick, no-drilling-required mod.

Here are the parts needed for the 15 minute oil mod (complete parts list here). I got the oil filter adapter, mounting bolt, and 0-ring from Mark Douglas. The hose and fittings came from Dave Dodge, Dodge Racing & Promotion.

Here's the adapter mounted to the engine, with the hose running up to the right.

The hose runs up the left side of the engine along the chrome coolant pipe, then back to the transmission.

Here's the hose connected to the transmission port. The shank of the double banjo bolt has been plugged with a screw, so the bolt both plugs the transmission oil port and connects the hose to the existing metal oil line. You can't see them here, but to seal the joints there are three crush washers around the two banjo fittings.

There were two installation issues on my bike:

The adapter moves the oil filter forward into the frame. Fortunately, the oil filter for the GL1500 Gold Wing is smaller yet has the same specs as the stock filter, and fits perfectly.
On California-spec Sabres, a charcoal canister is also in the way and must be relocated. Since I don't live in California I relocated it to my spare parts shelf (along with the stock saddle, fork springs, fork brace, headlight, . . .).

So here's my simple, bolt-on, non-invasive, reversible oil mod. The installation adds about 15 minutes to an oil change. The mod doesn't increase my top speed but it should keep my bike running longer.

Last updated 20 Mar 2003