750 oil pressure relief spring mod revisited

[Dakotakid]

Last weekend, I managed to bring home an '82 GS 750EZ which is cosmetically very nice. The bike has only 19,xxx miles.

I was under the assumption (time to have fun with that word....sheesh) that this engine was a ball bearing little brother to my 850GZ....wrong. I really should have done more reading and digging before letting go of my money.

The bike has been sitting in the last two years. However, the engine sounds very nice even before I begin performing the usual carb, valve adjust, etc. stuff.

I have been digging to find specifics on the oil pressure relief spring modification. I understand that there was a service bulletin (many years ago) and that it was recommended that two 6mm spring washers (are these the "wavey" looking ones???) for a total of 2.5mm are added (apparently) under the relief spring to increase oil pressure to the cam and cam gear. (Look...I have been really trying to understand the mechanics of this).

However, where is the oil pressure relief valve located? Is it on the oil pump itself? Do I need to pull the lower engine pan and proceed through there?

Clearly, I am rather clueless. I have spent time looking at Babbit's parts/engines diagrams, but remain ignorant. Did someone ever make a pictoral or detailed write-up on this?

Any concrete/basic help would be good as I am really regretting bringing this bike home. I think I better cancel the ad for the sale of my GPZ...really! I was thinking I could find an alternative to the lean-forward riding position by purchasing this sweet-looking GS 750. Crap.
Charlie

[Nessism]

You need to drop the oil pan to access the relief valve. I'm not personally familiar with this mod other than reading about it here, but I believe the idea is to increase preload on the spring, which ultimately will increase high rpm oil pressure.

When you get to the point of doing the work please take lots of photos so the process can be documented for those that follow.

Good luck

[Dakotakid]

I now see (by using the Clymer manual I received....which I forgot about) that the pressure relief valve is located next to the oil pick-up screen.

Can anyone tell me how to tell if this modification has already been preformed by a previous owner? According to my Clymer photos (quite small), there appears to be a circlip located in the inferior (bottom) aspect of the pressure relief valve. Would the shimming take place on this lower end?

I would sure be willing to photo-ize the process when the time comes. The time may not arrive until fall. The other bikes beckon! And they don't need to be mod-ed/rebuilt to ride.....crap!

[GregT]

See the thread by Laverda1200 - cam chain broke in 1989,in this section.
If yours looks like the picture he posted it hasn't been modified.

[Dakotakid]

I thank you very much and I apologize. I was on this thread earlier today and I never followed to the 2nd page. That is a very nice picture.

Spring washers are those wavey/wrinkled-looking ones? A standard washer or washers 2.5 mm thick isn't good enough?

Just wondering why spring washers are specified....that's all. (If you don't ask....you'll have a delay in knowin').
Charlie

Edit:
http://www.thegsresources.com/_forum/showthread.php?t=181119&highlight=oil+pressure+rel ief+valve&page=2

[GregT]

Why spring washers ? Ha - probably because the first guy who tried shimming the relief valve had them on hand.
Once the mod worked the information would go up the chain to the distributor..."joe Soap did this and it worked" Then the distributor enshrines it in a service bulletin and it becomes gospel....
I reckon 2 X 6mm spring washers equals about 3mm or say 1/8 in of extra preload on the spring.

[TheCafeKid]

Ne'er done the mod, read about it. Never have owned one of those bikes (well, one, but the motor was already toasted on that one..) to do the mod to. I think given the knowledge that a problem *could* arise, it's a worthy mod. Pulling the pan will also allow you to clean it out and make sure the sump screen is clear. Following all of this up with RELIGIOUS oil and filter changes should lead to alot less worry. Change it early and often (1500-2000 miles)
And your air filter. The less dirt introduced to the system the less chance of it blocking up one of those tiny ports.

I dunno if he still sells em, but one of renobruce's pressure gauges might be a worthy investment too. I know all GS have a pressure light, but the amount of pressure it takes to shut that off is minimal, and if it comes on, chances are it's too late anyway. Just my .02

[laverda1200]

Hi Charlie

it was GregT (who I know from another forum we both frequent) who gave me the information on the 750 oil pressure relief spring mod.

I posted a close up shot of the oil pressure relief assembly in my own thread here, as GregT pointed out to you. http://www.thegsresources.com/_forum...d.php?t=181119 post #17

basically, the oil pump pushes the oil against the oil pressure relief valve, and at some point the increasing oil pressure lifts the little valve off its seat and bleeds off oil into the sump. When the oil pressure relif valve opens, it reduces the oil pressure back to whatever the factory preset is.

what determines the pressure bleed off point is the spring tension in the assembly. What we don't know is what the free spring length should be, or how much spring tension has been weakened over the past 30 years or so.....

anyway, if you take the oil pan off with the engine still in the bike, the oil pressure relief valve is the thing sticking down the furthest into the pan, with the ciclip in the end of it. The assembly just unscrews easily with a wrench or socket, and once you have it out, use a pair of circlip pliers to release the spring and the plunger at the bottom.

personally I just used two stainless steel flat washers sized to fit inside the spring end cap, riding on the top of the spring, so the circlip still installs on top of the end cap itself, looking at the unit without taking it apart you would never know it has been shimmed.

so, all this modification does is make the spring pressure harder for the oil pressure to overcome, resulting in the oil pressure inside the engine increasing. How much does it increase? I have no idea as yet, my motor is still completely apart waiting for a new cam chain and a gasket set to arrive.

what I would like to see is someone put an oil pressure guage on the motor before and after the modification to see how much of an effect this simple modification may have on oil pressure.

It also would make sense to source either a brand new oil pressure relief spring or an entire brand new assembly just so you are starting from whatever oil pressure setting the factory set, but I haven't looked into that yet.

as for the durability of a plain bearing engine versus a roller bearing crank, GregT and I both work with roller bearing crank engines in Laverda triple engines, and servicing a roller bearing crank involves using a 30 to 50 ton press to disassemble each crank section to remove each rod and replace the roller bearings, a plain bearing engine with a one piece crank and bolted together rod ends is a delight to service and cheap and easy to replace crank bearings.

A plain bearing engine will run for hundreds of thousands of miles (most car engines, for example) as long as it has enough oil pressure and regualr oil changes. The crank bearings in the 750 engine I am rebuilding are all perfect, no problems whatsoever in the bottom end, there just wasn't enough oil flow to the cams and rockers and one of the cam rockers seized on the rocker arm shaft, preventing the exhaust cam from rotating, which snapped the cam chain.

on disassembly of the motor it was clear that the former redneck owner wasn't much for oil changes, and some of the oil flow passages were partially obstructed with dirty crap that had accumulated, obstructing oil flow to the head.

I am confident that on reassembly with cleaned motor internals, and regular oil changes, this motor will be very durable.

Paul

[UncleMike]

Which motors does this affect, specifically? Just the early 16v 750s?

[gearhead13]

Which motors does this affect, specifically? Just the early 16v 750s?

Yes, the 80-82 750's.
I completely pulled my 750 apart, checked the main and rod bearings, the mains looked real good, so I just replaced the rod bearings. The engine had 62k km on it. They have two brass oilway restictors that are located in between the cases and cylinders that have o-rings to help hold them in place. I replaced the o-rings and you could enlarge the restrictors for more oil to the top end if you wanted. After the rebuild with wiseco 816cc pistons I ran it real hard at times for a couple years with a few buried tachs from missed shifts, never had a problem with it. I ran it for 400km with the oil temp pegged out and at 7-9 k rpm. I never shimmed the pressure relief valve, although I should have I guess.
EDIT: I always ran Castrol 10w-30 motorcycle oil and changed it regularly.

[7981GS]

They have two brass oilway restictors that are located in between the cases and cylinders that have o-rings to help hold them in place.
I replaced the o-rings and you could enlarge the restrictors for more oil to the top end if you wanted.

Thanks for sharing that tip.
I dont believe that I have heard about it before.

Daniel

[gearhead13]

Parts #17 and 18 in the pic, one on either side.

[laverda1200]

ahd here is a photo of the oil jet in the top of the engine case, where it jets upward though the cylinder block to the head. There is an identical oil feed jet on the other end of the engine case. They are slotted, and turn easily, I haven't tried to remove one, yet...

Paul

[GregT]

Although slotted, they're not threaded if I remember...
Yep, pull them and clean the passages.

[laverda1200]

Hi GregT

both crankcase halves fit in my parts washer, but neither fit in my ultrasonic which is only big enough to do carbs in. The crankcases spent a night in my parts washer tank with solvent circulatiing, then got blown out with compressed air, but I didn't think to take the little brass jets out. I'll pull them out and really blow out the passages behind them again.

I am going to take the barrels and head over to my local friendly machine shop and have them "hot tanked" for a few hours, that will get rid of any internal crud in those componenets, and I am going to pull all the engine case block/head retaining studs to clean and polish them, there wasa ton of crud built up around the engine studs impeding oil flow as well, I am determined this engine will not exhibit any head/cam/rocker oiling issues.

I am afraid "hot tanking" the pair of engine cases might well strip the case paint, and I am not inclined to want to repaint them for this cheap and dirty rebuild.... I am only doing essential mechanical systems, engine/brakes/suspension/tires, nothing cosmetic other than a clean up and a cheap $30 new seat cover

Paul