Simmy's Naked Turbo Project

And a special thanks to you Len, without XJ4ever this project would have been very difficult if not impossible.

 

Not to take anything away from your project, which looks fantastic, but my experience with the Turbo Seca is that the lower compression ratio and weight resulted in less "spirited" performance at low speeds (where the 550 and event 650 seca would win out). However, keeping the turbo spooled at highway speeds, power would be easily accessible. At those speeds, the fairing would help tremendously, even if the speedo ran out of room (in US at least).

As far as "sleepers" go, I do like the Seca looks a lot more than the Maxim. That paint job and decals really looks like it could have been a factory option, so hat off. I don't know if the market should have approved in the 1980s (insurance costs were a big factor as well), but it helps to have a stock Turbo Seca as a foil

Hopefully the front end swap helps a lot compared to the 650 Turbos (I never got mine to feel quite dialed in even after cartridge emulators). How's it handle?

 

I agree with this, back in the 80's when I rode a Seca Turbo my bike was always a match for anything from about 70-100 mph, including 1000 Interceptor & FJ1100. It seemed everyone I rode with had either of those. I next acquired a CBR1000 Hurricane and was able to pull ahead.
Being from Canada and riding too often in the cold I am an advocate of fairings but I can also appreciate the streamlining. I think the fastest unfaired bike I had was the MT-01 which was good for almost 150 mph, now that was fighting the wind.

This comment will have to wait as I've only ridden it about an hour. It's stable that's about all I can say for now. Really looking forward to riding some curvy roads.
Shedding all that weight has to improve the off-boost performance.

 

Curvy roads in Ontario? Tell me where they are.

 

Actually the Eastern part of Ontario has some amazing roads, but I get your point it’s all 3 hours away. Farm country where you and I are is all plotted in squares, boring.

 

I spent some time digging into my spare motors Easter weekend.
I tore down my spare 650 Turbo and the 900 I have.
I thought about making a 738 with the original motor in the bike now by simply installing 67 mm block & pistons.
Instead I've decided to keep my original 653 and build a bigger motor on the side.
I can take my time and still have a running bike to ride, maybe do the motor swap next winter.

The 650 Turbo was stored outside without the clutch cover so there was rust even inside the motor.
Even the oil pump drive chain had rust.
I didn't take any pics of the main bearings of the Turbo motor but there are deep scores in the main journals.
I've included some pics below of the 900 and there are a few which are questionable and should probably be replaced.
I've read here that the colour code of the bearing shells has not been correlated with a number?
Can someone fill me in on that? @chacal lists blue, black, brown, green, yellow so I assume this is 1-5?
I'm planning of course, to go through the plasti-gauge process and verify the tolerances.




here's a pic of the 900 oil pump next to the 650T.
Drive gears I believe are the same I think, 25T but the driven gear on the 900 is 30T and the Turbo is 23T.
Chains are obviously different length so I'll need a new one here as the Turbo one is rusty.
The shaft in the pic is from the Turbo, you can see the rust.


I verified the lower cases are pretty much identical, at least where the oil pumps mount.


I'm undecided on which cases to use, leaning towards the 900's just because the crankshaft was originally fitted to them.
I snapped 2 of 3 bolts removing the primary chain guide out of the Turbo cases so that would need to be cleaned up.
I will heat the 900 before I remove them. Turbo's guide was ready to break in 2 pieces.
The 900 cases have the boss for the oil feed to the turbocharger, just not drilled and tapped for the check valve.
I'm pointing to it with the screw driver. I think they all have this boss.

So the plan is to build the bottom end with the 900 cases and the 900 crank, 650T oil pump and oil pan.
I need to keep the physical dimensions of this motor the same since there is just enough room between the petcock and #1 carb hat.
The 900 pistons are shorter which helps my case, I believe the barrels are the same height.
I'll have a look at the rods, obviously need to use the 900's as the bolts go in from the top, otherwise the bolt heads would hit the cases with that 60.5 mm stroke.
I'm just curious if they are the same length.

The 900 has 9.6:1 CR which I will need to drop to about 8:1.
the 650 Turbo is 8.2:1 and the Kawasaki Turbo was only 7.8:1.
I'll be using 650T heads which I plan to dish out around the edges to match the larger bore.
Ideally I can get some forged pistons made and I'm going to ask for a quote from https://www.jepistons.com/
I believe they could make exactly what I need to drop the compression without adding extra base gaskets.
We'll see what that might cost.
I could go 1 mm larger to 68 mm and clean up the cylinders with a fresh bore job.
I just ordered a low mileage 650T cylinder head from eBay.

 

I used an XJ900 engine and installed forged pistons from JE pistons using stock compression. I used the XJ650 turbo oil pump and chain gear which allowed me to use the scavenging port of the 650 oil pan. You can definitely tap the port next to the oil filter, I did. I get 150 hp on a conservative tune. Your biggest limit on these bikes is the ridiculously low gear ratio, but you'll get to 125-130 mph really fast! My plan is to modify the middle gear. I found the right combo of gears to make it possible, but custom middle gear will be $.

 

Awesome info @skylrk62 are you saying you kept 9.6:1 CR?
If you don't mind, can you send me a PM and tell me what kind of money 4 custom pistons run?
Or just respond here, I don't care.

In my case I think the limiting factor will be the 30 mm carbs and the small valves.
My gear ratio is now even shorter with the 16" rear wheel on it, that's all ok as it brings on boost sooner!

 

I'm not 100% on the ratio being exactly, but within .1-.5 of the original. I believe it cost me $800-850 for a set of custom pistons (JE part no# WD-05702). This was in 2017, so it may be more or less now? I fuel injected my bike, so I can't help with your carb setup.

 

That is a great price for forged pistons.
I don't think it's worth the attempt to rebuild this motor then taking the chance of melting it down with the OEM 900 pistons.
Definitely the way to go.
My challenge will be to order the exact piston I need so I can put them straight in with the desired CR.
I'm planning to put it together first with the stock 900 pistons, modified combustion chamber in the head and see what the CR is.
Then I could tell JE how much deck height to take off the piston. Going up 1mm in the bore will throw these calcualtions off though.
I've even thought about ordering a 68.5 mm block and pistons from Germany.

I would expect your fuel injection and inter-cooler probably tolerates higher pressures than my basically stock set up will allow.
What bore size did you go with?

 

Stock bore, but had special modern improvements. I'll send you specs in a private message.

 

Now that's just not playing the game...
Anyway, for @Simmy , why use the 650 turbo head and carbs? Is it that the 900 ones bigger and will foul the petcock?
I know the carbs are bigger, but are they taller?

 

Hi @Minimutly I'm posting this from the Yamaha Turbo manual, I'm pretty much stuck with these carbs.
The 900 head is physically bigger as it carries another bearing support but the Turbo has special cams with less duration, and they won't fit in the 900 head.
I'm not certain if that is for performance with turbocharging or emissions with turbocharging. Suspecting the latter, I would think longer duration combined with pressurizing things might dump unburned fuel out the exhaust, this would not be good for emissions but also likely not good for the turbocharger, I'm just guessing.
On the Turbo forum there is mention of running an XJ700N exhaust cam retarded 3 degrees but I've not been able to learn anything more about this.
The exhaust valve has 16G (the Turbo model designation) embossed on the surface, I'm not sure if it got some exotic metal to withstand the additional heat or its simply a different size than the other 650/750 valve.
So pretty much resigned to the puny carbs and inlet/exhaust valves.

 

You could do the traditional suck-through design and use a single large carb?

 

Just remember, if you plan on going over 100 hp, you'll most likely need a custom lockout clutch.

 

Now we're getting carried away with things @skylrk62 , you're a bad influence.
When it comes down to it there is a reason I love riding thumpers, nothing better than the soothing pulse of simplicity.

 

Yes I can see why you wouldn't want to change the carbs. It may not be the end of the world, since the air going through them is denser, and more air just needs to be higher pressure to recover any losses. You could regrind the 900 cams - the turbo cams have less duration - probably to keep low speed torque up and use less fuel. The downside is you will lose performance on boost. I get the "keep it simple" thing too.

 

I didn't want to admit it but I had huge disappointment with this Turbo last weekend.
The previous weekend I changed the oil and restarted the bike and warmed it up, checked the level, everything was finally finished.
It was cold and wet so I shut it off, put the cover on and waited for a warm day.
So a warm day came last week and I decided to go for a good ride. I made it 5 doors down the street and it quit.
Walked it back home totally pissed.
It would start just barely and run on a couple cylinders, #4 was cold.
In my mind I'm thinking please don't be plugged idle circuits in any of the carbs.
It just wasn't getting enough gas to rev up.
Tonight I took the tank off and hooked up my aux tank with transparent gas lines so I could see what is going on.
This bike has 2 gas lines to hook up, one feeds the fuel pump and the other one returns excess fuel pressure from the regulator.
The lines were empty of gas so I followed the trick from @ManBot13 - put the sidestand down, put it in gear, turn it on and hold the starter button.
When you do this nothing runs except the fuel pump. I had to run the pump like this for several long minutes until I go all the lines full of gas.
I thought maybe the pump was just cavitated. Once I got enough gas the bike started up and I warmed it up and had it idling but I could tell its not right.
The new Walbro fuel pump I bought is just not pushing the fuel anymore, it was flowing a ton of fuel through the bike, now there's barely a trickle from the return line.
This has to be it. I'm going to test it on the bench just to be sure but this sure feels like a win to me!
I ordered this on-line a year ago from Summit Racing, I'm hesitant to get the same thing again but it fits nice and I know they perform when they do work.
Oh yah my new Turbo head arrived today, looks to be in nice shape, all exhaust studs accounted and clean threads on the intake side.
The cam caps came with it to, most of the heads on eBay are missing them. No cams though, I think the cams from the swamp rat motor are ok.

 

I got thinking about my fuel pump a little more.
The fuel system starts at the petcock and the Turbo has a positive shut when in the off position.
From there it goes through a metallic style fuel filter from Chacal straight into the fuel pump.
I eliminated the guts from the fuel check valve just before the carbs so I shut the fuel off when stopped.
Needless to say, in the 100 kms I've ridden it I already forgot to switch the fuel back on and had the motor running a short while like that.
So the question is, do you think I damaged this fuel pump by running it with the gas shut off?
There is no difference in the system from OEM except different pump. The Yamaha pump would tolerate this, will the Walbro?

 

this might explain things better. When the fuel is shut off the pump will see hydraulic lock, will it stop spinning or pull its seals apart? The pump is good for 130 LPH, mine is delivering probably .5 LPH.