Low oil pressure

1701 Views 3 Replies 4 Participants Last post by twisty, Sep 26, 2005

rustybob11

Discussion Starter · Sep 25, 2005

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I bought my 1984 GL1200I last December. 43K on frame with a 72K engine. She spent a lot of downtime as I fixed her up for use. Last July she popped her stator and became unuseable. I tore her down and replaced the stator and got her running again about September 22. I filled her wilth Motul 10W40 and Honda Coolant and ran her 30 minutes on the centerstand. Then I started a ride to cleanout the old junk. etc.

After a 10 minute ride on the freeway the OIL light came on. I shut her down and let the engine cool and limped home. I was shocked because I had never gotten this indication before.

I pulled the OIL switch and cranked her to clear the oil passage. After 5 seconds the oil came out in pulses. I bought and hooked up an oil pressure gauge.

First test: cold. She gave 25 psi at 1,000 rpm. No increase at 2,000+ rpm.

First test: hot. She gave about 12 psi at 1,000 rpm. No increase at 2000+ rpm, except 2 brief jumps to 25 psi at 2,000 rpm before dropping back to 12 psi.

I theorized that the oil pump relief valve was sticking, because she sat dry for 2 months in our 95+ temps. I added 8 ounces of Seafoam and ran her from cold to hot a few times.

Second test:cold. She gave 25 psi at 1,000 rpm. Instant increase to 35 psi at 2000+rpm. There is a hard limit at 35 psi as rpms are increased further.

Second test:hot. She gave 12 psi at 1,000 rpm. Instant increase to 25 psi at 2,000+ rpm.There is a hard limit at 25 psi as rpms are increased further.

Bottom lines: the oil pump relief valve got stuck from sitting 2 months dry in heat. The Seafoam freed the valve so it worked better. I am not comfortable with the 25 psi hot. I believe the pump relief spring has softened/shortened over the past 20 years and opens too soon, limiting pressure at 25 psi. My plan is to get a new valve, spring, etc and install them. Should I replace the rotors at the same time? BikeBandit only shows the outer rotor for $35.

Thanks, Bob Rust Albuquerque:jumper:

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twisty

· #4 · Sep 26, 2005

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rustybob11 wrote:

I bought my 1984 GL1200I last December. 43K on frame with a 72K engine. She spent a lot of downtime as I fixed her up for use. Last July she popped her stator and became unuseable. I tore her down and replaced the stator and got her running again about September 22. I filled her wilth Motul 10W40 and Honda Coolant and ran her 30 minutes on the centerstand. Then I started a ride to cleanout the old junk. etc.

After a 10 minute ride on the freeway the OIL light came on. I shut her down and let the engine cool and limped home. I was shocked because I had never gotten this indication before.

I pulled the OIL switch and cranked her to clear the oil passage. After 5 seconds the oil came out in pulses. I bought and hooked up an oil pressure gauge.

First test: cold. She gave 25 psi at 1,000 rpm. No increase at 2,000+ rpm.

First test: hot. She gave about 12 psi at 1,000 rpm. No increase at 2000+ rpm, except 2 brief jumps to 25 psi at 2,000 rpm before dropping back to 12 psi.

I theorized that the oil pump relief valve was sticking, because she sat dry for 2 months in our 95+ temps. I added 8 ounces of Seafoam and ran her from cold to hot a few times.

Second test:cold. She gave 25 psi at 1,000 rpm. Instant increase to 35 psi at 2000+rpm. There is a hard limit at 35 psi as rpms are increased further.

Second test:hot. She gave 12 psi at 1,000 rpm. Instant increase to 25 psi at 2,000+ rpm.There is a hard limit at 25 psi as rpms are increased further.

Bottom lines: the oil pump relief valve got stuck from sitting 2 months dry in heat. The Seafoam freed the valve so it worked better. I am not comfortable with the 25 psi hot. I believe the pump relief spring has softened/shortened over the past 20 years and opens too soon, limiting pressure at 25 psi. My plan is to get a new valve, spring, etc and install them. Should I replace the rotors at the same time? BikeBandit only shows the outer rotor for $35.

Thanks, Bob Rust Albuquerque:jumper:

Bob, with your 2nd hot giving12 psi at idlebut not increasing past the 25 psias the RPM's increased I'm sort of doubting a stuck relief valve. On all engines that I have seen a stuck relief valve the oil pressure would be very low at idle but increase linearly as the RPM's increase with no hard ceiling at a given psi.. As the RPM's increase the gpm would also increase so with a stuck valve you would have almost no oil pressure at idle, would be low through the range but would increase as the oil flow increased at higher RPM's (not stay at a fixed rate)..

Your problem sounds more like a partially plugged oil pump intake screen as the oil volume would then drop as the RPM's increased & could hit a fixed ceiling as the flow into the pump reached it's limit..

It could also be a weak relief valve spring that you spoke of but those don't usually get weaker with age as they are a wire wound spring & those seldom sack out with age.. They can get weaker with rust though as the rust thins out the wire in the rusted area.

My rule of thumb (well not not my idea but what I use) is 10 psi per 1000 RPM's so be careful running that engine at low oil pressure or you will be pulling the engine for bearings..

As far as the rotors go/ The service limit is in the manual so just measure them & use the wear limit data to make a decision.. If rusty replace them..

Twisty

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