Turbo 77 gs750 project

[OldSoul67]

I picked up a 77 gs750 a few years ago and hadn't done anything with it since. Well now that I'm fresh out of other bikes and have a lot more time on my hands i got it re wired and running, not running well though as it was nearly burning more oil than gas. So after rebuilding the head i decided i was already here and did  the 850 top end swap. Me being me i can't leave good enough alone I'm looking to add a turbo system and was wondering what kind of prep I'm going to need to do this. Is the oil pressure good enough? Do i need to weld the crank? Any tips will help. I'm not really looking to swap the motor this is really just something to wrench on and have fun with.

[Reinhoud]

Weld the crank? Hmm, when it was a 1000cc then defenitly, but I wouldn't be surprised if you just get away with it with a 750.

I think you get about the power output of a 1000. But when in doubt I would do it.

 

You probably need forged pistons.

When you use a ball bearing turbo you might be lucky with the oil delivery.

[OldSoul67]

24 minutes ago, Reinhoud said:

Weld the crank? Hmm, when it was a 1000cc then defenitly, but I wouldn't be surprised if you just get away with it with a 750.

I think you get about the power output of a 1000. But when in doubt I would do it.

 

You probably need forged pistons.

When you use a ball bearing turbo you might be lucky with the oil delivery.

These bikes are still pretty new to me so i wasn't completely sure with how much power i could get away with and stay relatively safe. When i re-did the top end i did put forged pistons in it so I'm covered there. I've been reading pretty hit or miss if the oil pump could handle it, i saw a few people changing out their oil pump gears on the larger engines with these ones to help out so i wasn't completely sure if it would work or not. May still end up trying to find something for that as well. Thank you

[jameskat]

The oil pump gear swap on the 1100 is usually to use the gears out of a 750 16 valve plain bearing engine which have a different ratio (spin the pump faster).

[OldSoul67]

2 hours ago, jameskat said:

The oil pump gear swap on the 1100 is usually to use the gears out of a 750 16 valve plain bearing engine which have a different ratio (spin the pump faster).

Is there any chance that the gears from a plain bearing engine would swap over to mine or would an external pump work better if i do decide to adjust my oil pressure for the turbo 

[Arttu]

The pump gears are the same for plain and roller bearing 750s. So unfortunately no help for you that way. However, most likely it's possible to add a restrictor on the oil channel somewhere between the filter and rest of the engine and take oil to the turbo from front side of the restrictor. This way you should be able to get high enough pressure even for a plain bearing turbo. I'm not very familiar with the 750 engines so can't tell exactly how this should be done but I guess it's doable. 

[OldSoul67]

12 minutes ago, Arttu said:

The pump gears are the same for plain and roller bearing 750s. So unfortunately no help for you that way. However, most likely it's possible to add a restrictor on the oil channel somewhere between the filter and rest of the engine and take oil to the turbo from front side of the restrictor. This way you should be able to get high enough pressure even for a plain bearing turbo. I'm not very familiar with the 750 engines so can't tell exactly how this should be done but I guess it's doable. 

I didn't think about using a restrictor. In that case i could drill and tap a hole in the center of the oil filter cover and run the line from there. I was planning either from there or from where the plug is on the right side to measure the oil pressure. Thank you

[Arttu]

I think you would get unfiltered oil from the filter cover. Not good for the turbo...

By looking the parts fiches it seem that you could do similar take-off plug in place of the oil pressure switch that I have used on my GSX.

[OldSoul67]

22 minutes ago, Arttu said:

I think you would get unfiltered oil from the filter cover. Not good for the turbo...

By looking the parts fiches it seem that you could do similar take-off plug in place of the oil pressure switch that I have used on my GSX.

I'll have to check when i get back, but that does look pretty similar to what i have. I didn't have the oil diagram on hand, so i was just kinda spit balling ideas. It looks like you drilled out a banjo bolt for the reducer and another bajo to go on top of that

[Arttu]

The big "bolt" in lower picture is the actual trick. It goes in place of the oil pressure switch, the tip goes into oil channel coming from the filter so it captures all the oil flow. Oil to the engine is bled through a small hole on side of the bolt. The turbo gets unrestricted oil flow from top of the bolt. Pressure for the turbo can be adjusted by size of the bleed hole. On top of everything there is also a pressure switch from some car to replace the original pressure switch.

[RobNukem]

If you can find a Clymer manual for the GS it had a few pages on tuning a gs750 and a few lines on turboing it, I haven’t seen it for a while so can’t remember exactly what’s in there. A friend at the time raved about it being better than a Haynes manual, I’ll try to dig it out. Might be worth getting.

Edited February 6, 2021 by RobNukem
Left out an important word

[OldSoul67]

8 hours ago, Arttu said:

The big "bolt" in lower picture is the actual trick. It goes in place of the oil pressure switch, the tip goes into oil channel coming from the filter so it captures all the oil flow. Oil to the engine is bled through a small hole on side of the bolt. The turbo gets unrestricted oil flow from top of the bolt. Pressure for the turbo can be adjusted by size of the bleed hole. On top of everything there is also a pressure switch from some car to replace the original pressure switch.

Alright, that makes sense. I'll see what i can put together. Thank you again

[OldSoul67]

5 hours ago, RobNukem said:

If you can find a Clymer manual for the GS it had a few pages on tuning a gs750 and a few lines on turboing it, I haven’t seen it for a while so can’t remember exactly what’s in there. A friend at the time raved about it being better than a Haynes manual, I’ll try to dig it out. Might be worth getting.

I might check that out. I got ahold of an original maintenance manual so i could adjust the valves and have the right torque specs, however that was before i decided to get this far into it.

[Reinhoud]

I think there's an oil pump from a GSX750 (plain bearing) what is about 5mm wider then the GS750 oil pump what fits the GS750.

There are 10mm wide pumps, and 15mm wide pump, the 15mm wide ones do fit.

 

But I don't know what goes/comes from where.

[Reinhoud]

On 2/5/2021 at 10:47 PM, OldSoul67 said:

Is there any chance that the gears from a plain bearing engine would swap over to mine or would an external pump work better if i do decide to adjust my oil pressure for the turbo 

You never get pressure with a GS engine!! Only when the engine is cold, I experimented with that.

I've got a GS1000, with a wider pump, and I had an even wider home made pump and with 750 gear ratio, restriction in the oil gallery to the gearbox, and still no pressure, it did raise the pressure when cold, but that dropped when the engine warmed up.

[Reinhoud]

On 2/7/2021 at 3:43 AM, OldSoul67 said:

I might check that out. I got ahold of an original maintenance manual so i could adjust the valves and have the right torque specs, however that was before i decided to get this far into it.

Valve clearence is between 0.03 and 0.08mm, cold

This is for the 1000, I think the 750 is the same

 

Head nuts are 35/40Nm

Rotor 125Nm

Clutch hub 70Nm

M6 is about 10Nm

M8 is about 14Nm

Edited February 8, 2021 by Reinhoud

[OldSoul67]

3 minutes ago, Reinhoud said:

Valve clearence is between 0.03 and 0.08mm, cold

This is for the 1000, I think the 750 is the same

The 750 is the same, i haven't had a chance to put everything back together again yet, so it'll still be a minute before i have to get it done

[OldSoul67]

14 minutes ago, Reinhoud said:

You never get pressure with a GS engine!! Only when the engine is cold, I experimented with that.

I've got a GS1000, with a wider pump, and I had an even wider home made pump and with 750 gear ratio, restriction in the oil gallery to the gearbox, and still no pressure, it did raise the pressure when cold, but that dropped when the engine warmed up.

Yeah, that's what I've been worried about. After it's warmed up the book says it's supposed to read over 1.42psi i think thats around 0.1 kg/cm² or something like that

[Arttu]

9 hours ago, Reinhoud said:

You never get pressure with a GS engine!! Only when the engine is cold, I experimented with that.

I've got a GS1000, with a wider pump, and I had an even wider home made pump and with 750 gear ratio, restriction in the oil gallery to the gearbox, and still no pressure, it did raise the pressure when cold, but that dropped when the engine warmed up.

Beep, wrong! With the mod pictured above I had about 3-4 bar pressure for the turbo, warmed up. I run a plain bearing turbo with that for about 20 000km without issues.

[Reinhoud]

16 hours ago, Arttu said:

Beep, wrong! With the mod pictured above I had about 3-4 bar pressure for the turbo, warmed up. I run a plain bearing turbo with that for about 20 000km without issues.

How? Just because of that restrictor in your (home made?) banjo?

 

You have 3-4 bar pressure in the turbo oil feed line?

 

 

Edited February 8, 2021 by Reinhoud

[Reinhoud]

@Arttu, I try to understand your solution. Looks like your solution is a hell of a lot simpler then mine

 

1 is the main restrictor, what fits in the oil feed straight from the pump what goes under the oil pressure switch? The small hole allows oil flowing to the engine.

2 is a spacer?

3 and 4 I can't see what they do

5 is for oil pressure switch?

6 is turbo oil feed line?

 

Getting oil pressure isn't hard, you just restrict the flow, problem is where to restrict it, and make sure the rest of the engine gets the right amount / pressure.

If you have 3-4 bar when warm, don't you have too much pressure when the engine is cold?

 

As far as I can see is that you restrict the oil coming from the pump, but where you connect your oil feed line, wouldn't you lose that pressure straight away?

 

How do you do the scavenge from the turbo?

 

Interesting, different people, different solutions.

I always look at the ways of how other people do it, I usually can learn something from that, mostly I do a mix and match from different ideas.

 

 

Edited February 9, 2021 by Reinhoud

[Arttu]

@ReinhoudYou got it pretty much correct:

1: Correct.

2: Yes, spacer. Only needed since I couldn't make threads up to head of the bolt.

3/6: Oil pressure switch for oil light. 0.3 bar, from some random car.

4: Banjo bolt for turbo feed line.

5: Turbo oil feed line.

You are right, it's somewhat tricky to be sure that all parts of the engine get enough oil after messing up with the system. But it helps to figure it out if you keep in mind that the oil pump is positive displacement type meaning the flow isn't significantly affected by pressure. So if you add restriction after the pump the pressure before restriction goes up but oil flow after the restrictor remains about the same. So with this modification oil flow to the engine is reduced only by amount that goes through the turbo, which should be relatively small with most of the turbos. In my case I installed also 750 pump gears at the same time with the turbo system. To verify the result I measured the pressure from the crank oil gallery before and after modification and the result was the same or even more after the mods. So the engine was still getting at least as much oil than as stock.

However, this mod is far from ideal. The pressure for the turbo varies a lot depending on rpm and oil viscosity. So as you said, with cold oil the pressure is much higher and it's a good idea to keep revs low until the oil is warmed up. When the oil is hot the pressure at idle drops pretty low, below 0.3 bar in my case. But at rpm where the turbo spools up there was always pretty good pressure so the turbo was happy.

Scavencing was just gravity drain to the sump plug in the first revision. Later on I made a deeper oil pan with dedicated connection for the oil return.

[Reinhoud]

46 minutes ago, Arttu said:

@ReinhoudYou got it pretty much correct:

1: Correct.

2: Yes, spacer. Only needed since I couldn't make threads up to head of the bolt.

3/6: Oil pressure switch for oil light. 0.3 bar, from some random car.

4: Banjo bolt for turbo feed line.

5: Turbo oil feed line.

You are right, it's somewhat tricky to be sure that all parts of the engine get enough oil after messing up with the system. But it helps to figure it out if you keep in mind that the oil pump is positive displacement type meaning the flow isn't significantly affected by pressure. So if you add restriction after the pump the pressure before restriction goes up but oil flow after the restrictor remains about the same. So with this modification oil flow to the engine is reduced only by amount that goes through the turbo, which should be relatively small with most of the turbos. In my case I installed also 750 pump gears at the same time with the turbo system. To verify the result I measured the pressure from the crank oil gallery before and after modification and the result was the same or even more after the mods. So the engine was still getting at least as much oil than as stock.

However, this mod is far from ideal. The pressure for the turbo varies a lot depending on rpm and oil viscosity. So as you said, with cold oil the pressure is much higher and it's a good idea to keep revs low until the oil is warmed up. When the oil is hot the pressure at idle drops pretty low, below 0.3 bar in my case. But at rpm where the turbo spools up there was always pretty good pressure so the turbo was happy.

Scavencing was just gravity drain to the sump plug in the first revision. Later on I made a deeper oil pan with dedicated connection for the oil return.

Thanks! Much appreciated.

Ah, now I see the pressure switch..

 

What you say in the 2nd section is what I expected..

I thought a little bit in that direction too, but was too unsure about results.

 

 

Edited February 9, 2021 by Reinhoud