Dodged disaster?

[Guido Valvole]

I rode my 1979 V50ii to a dental appointment last Thursday, as it had the most fuel in it. Hot day, as in 105F or so outside the office. As I turned into the parking lot, the oil light came on. It had flickered a few weeks earlier just as I pulled into my driveway, and a dipstick check showed oil at the fill level but not below. So I added about half a quart of 20w50 and all was well.

Checked level when I got out of the appointment, fine. Turned it on, no problem. Headed home via a friend's house for a dip in his pool. Halfway there the light started flickering at idle so I kept revs up. No problem. Then came on as I turned into his driveway.
A few hours later, repeat. All was well until a series of stoplights about a mile from home. Long red, of course. Pulled over to let things cool (yeah, right…) and coasted and pushed most of the rest of the way back. Had to go up steep hills a couple times, light on for no more than 30 sec max.

Started fine the next day, oil light went out as soon as it fired up. Wanted to change oil today, started fine, normal light, then on within 50 feet of leaving driveway.

Next step? I was thinking the oil got thin in the heat, but it should have recovered at least a bit after a week of cooler temperatures. Oil pump problem? Any way to check that other than pull a valve cover and get sprayed? Anyone have any experience with old smallblock oil pumps? Hoping not to have to do an engine rebuild, too many other projects already…
Thanks for any advice. No ugly noises from the engine. Sensor's gone bad? Now to find it and see if there's anything obvious like loose or oily wire. Thanks in advance!
cr

[pete roper]

Chances are it's the pressure switch which lives in the valley above the rear cam bearing. If you've got the original airbox you'll need to pull that to get to it and that is, if I remember correctly, a prick of a job!

Whatever you do do NOT move the crank or spin the engine when the sender unit is out as it also acts as a locator dowel for the cam! Take the old one out, put the new one in, don't touch anything else while doing it!

Pete

[pehayes]

You could pull a valve cover and run the engine to see how much oil is sprayed out.  Its a mess, but you can clean that.
My bet is on the sender.  Had similar symptoms on several Guzzis.  Special sender on this model has a long, deep probe to anchor a cam bearing.

Patrick Hayes
Fremont CA

[Chuck in Indiana]

Nothing to add. Listen to the men..

[Antietam Classic Cycle]

The V50 IIs I've worked on have an "adapter" that locates the cam, with a normal pressure switch.





Adapter:




The one piece switch/locating pin seems to have started with the V50 III.

[Kev m]

I've been on a lot of air-cooled motorcycles, in a lot of extreme conditions. I've never, not once, had an oil pressure light flicker because the oil has lost viscosity or "thinned" at temperature.

[Old Jock]

Happened to me Kev with the Daytona engine.

However you are correct IMHO, that if there is no other underlying problem the oil light coming on, shouldn't happen.

I'm still trouble shooting the Daytona (it's is currently in bits with new mains getting installed) as there is a pressure problem as well.

The one and only time I've seen a low pressure light and when I stopped the oil temp was at 120C (248F) and the pressure somewhere between 5-10psi, that will inflict damage in a VERY short time and probably wreck the engine in about 5 minutes or less.

However as Pete has said it's more likely to be the switch so don't panic.

I now install a pressure gauge and one of these stupid temp dip sticks, but both of them together immediately showed the problem and stopped me wrecking the engine

[Chuck in Indiana]

when I stopped the oil temp was at 120C (248F) and the pressure somewhere between 5-10psi,

that's a pretty normal oil pressure at idle as far as I know..

[Lannis]

that's a pretty normal oil pressure at idle as far as I know..

Certainly normal for the bikes where I have oil gauges, but they're all old Brits so maybe they don't count.   They DO have plain bushings as main bearings, though, so they need oil pressure and that's enough at idle.

I didn't read this thread at first - I thought it was an edgy new Chrysler model roll-out for 2020 ....

Lannis

[kirby1923]

that's a pretty normal oil pressure at idle as far as I know..

I can confirm that! Ha!

When people ask me about how hard it was to put a pressure gauge on my CX I tell them that if you do install one, prepare to be shocked, not for the faint!

I'm finally used to it!

[Kev m]

Happened to me Kev with the Daytona engine.

You're saying the oil lost viscosity and/or the oil thinned that much do to heat that it caused the light to flicker?

[wirespokes]

I've been on a lot of air-cooled motorcycles, in a lot of extreme conditions. I've never, not once, had an oil pressure light flicker because the oil has lost viscosity or "thinned" at temperature.

I guess that's what a woman friend thought when her R90 oil light came on about five miles from home. Almost made it too.

[Kev m]

I guess that's what a woman friend thought when her R90 oil light came on about five miles from home. Almost made it too.

And in her case what happened?!?

[Old Jock]

You're saying the oil lost viscosity and/or the oil thinned that much do to heat that it caused the light to flicker?

It didn't flicker it came on rock solid, the bike wasn't idling I was doing perhaps 20-30 mph. Unlike Chuck I've never seen the pressure that low 15 perhaps but not below 10.

I won't bore you with the story but yeah I think that the temperature was so high the oil viscosity had dropped due to the high temperature and the pump wasn't able to maintain pressure.

This bike has a problem and I'm pinning my hopes on the mains, the tolerances of both were within spec but just, both at the upper end. The journal on the front was close to minimum, I couldn't get a mic in to measure the rear journal. I've been through all the other likely culprits to no avail.

On this bike on first start with cold oil the oil pressure is around 50-55psi, for me that's low both the LM 1000 and 1100 lump will run up to their relief valve settings of around 60 and 70 psi respectively, the Daytona struggles between 50-55psi.

Apologies it was not my intenion to hi-jack the thread

[wirespokes]

And in her case what happened?!?

Come to think of it, her oil light probably wasn't flickering. The engine seized and if I recall correctly, the rod snapped. She must have ridden five or seven miles without oil pressure.

[Guido Valvole]

Thanks, everyone, for the advice and stories. Further investigation this morning. Light stayed on solidly, no flickering. No oil out of the top end, but it may take a while for it to get up there? I only spun it for a few seconds... when the bike was new to me one of the oil breather lines came loose and sprayed my leg, but that was about 15 minutes into the ride.

Bike came with a loop-type breather box and K&Ns. First box had a flapper valve failure a few years ago. Lots of hose clamps and rubber lines and potential for oil seepage and yep plenty of oil in the valley between the cylinders. And *all over* the oil sensor. I pulled the connector off and cleaned it. Then sprayed with WD40. Still a solid red light. More WD40 and wait a while, look ma! No red light! Oil is a pretty good insulator... However, it doesn't light when I put the key in the ignition, before hitting the start button so maybe the bulb burned out after 40 years. Further investigation needed.

[Kev m]

So to bring this full circle.... my original point is one of skepticism that this would likely result from JUST HEAT and thinning of oil.

That oil is, at least when decent quality and remotely in spec, probably not going to be the culprit (IF PRESENT).

That's where I was going with my line of questions and related experience.

Of course, I've used nothing but high quality synthetics for a couple of decades now, including in Harleys, so I've got that skewing much of my anecdotal evidence but still....

[wirespokes]

My T3 had the oil light on (sometimes off) the whole time the PO owned it - a year or two, but not many miles. I replaced the oil pressure sender and that fixed it. I recall one of my BMWs (think it was the R11S) having a problem with a flickering oil light - turned out to be water after a wash.

[Guido Valvole]

Oops. Oil light was out because I'd disconnected the wire to the sensor. Put that back on, light stays on. So no need to take the instrument pod apart, yay. Will order a new sensor. Seems like there's one that was used on V50 II and III and most big blocks (according to info on the MG Cycle website) Maybe an upgrade to the earlier one if such (as Charlie wrote). Part number is the same in both my V50 and V50iii/Monza books.
cr

[Diploman]

I believe it was only the V65 that was fitted with an unusual oil pressure sender that serves as a cam locating dowel.  AFAIK, the V50's all take the same conventional sender as the big blocks.

[Frenchfrog]

Nope...all the small blocks used that oil sender. tow versions...one is a two part (cam locating "bolt " and the a separate oil pressure sensor screws into that) the other is one piece doing both functions.They are interchangeable.

[Guido Valvole]

Going by what's on the MG Cycle website, the common one (which I ordered, listed for both the V50ii and *some* iii/Monza although part numbers are the same in the parts books I have) is just the top part, not the locating dowel, and has an M 12x1.25 thread. The other is one piece and has an M12x1.5 thread. Parts shipped today so I'll find out if it was the sensor or something ugly early next week.
cr