Simmy's Naked Turbo Project

I had the exact same thought after I wrote that.
On the other hand it would be so much cheaper to just swap in the new block and pistons to the original motor. I like the idea of having the original 650T motor unmolested but it just becomes a heavy lump I have to find a corner to store it in.
I figured if I ever sold the bike it would be worth more if it included the numbers matching motor in original state. And I could always sell the 772 separately if it was a complete motor.
Also provides the option of going back if for any reason the 772 doesn’t work out.

 

My 772 is closer to reality.
The block is vapour blasted and machined shorter, 3 sleeves shortened the same and pressed back into the block.
All according to plan until my engine guy fumbled the last sleeve and a big chuck broke off when it hit the concrete floor.
Shit happens. Now waiting for another 31A (67mm) cylinder block from Germany just to salvage another sleeve.
He suggested machining a replacement but the blank is 8 weeks delivery.
I'd rather go ebay Germany route so I know all 4 will be the same.
Once all 4 sleeves are in it will get a fresh bore from 67 to 68.5.
The 68.5 pistons are vapour blasted and look new.

I ordered a set of piston rings from the UK, not many vendors out there with standard rings for the 58L.
UK Yamaha dealers all show rings no longer available.

 

I received another 31A cylinder block and dropped it off with the shop.
I have in my hands new ring set for the 58L
Shouldn’t be long until the block is done.
He actually had the tap for the knock sensor so that is complete.
So other than paint it will be ready to bolt in.

I’ve decided to just pull the top end off my original motor.
I will have the block, pistons, rings, wrist pin ready to bolt in. Those 4 items are the only parts I’m changing and the block is the only modified Yamaha part.
Once I get the block back I’ll start tearing my bike down again.This makes so much more sense than rebuilding and changing out another motor. A lot cheaper to.
Same head and cam chain. I could have this ready for the spring.
63 year old rider (soon) 42 year old bike and I’m just as excited to ride it now as ever.

 

900 block tapped for the knock sensor
Nice of Yamaha to cast in the boss for this

 

The vapour blasting looks pretty good in the pic he sent me.
Should be good to accept paint.

 

Forgive me, I don't recall what head you'r running with this. If it's a 650/750 I would be looking at getting my die grinder out to open up the exhaust ports, and then maybe looking at some of the same on the inlets - effectively a free-er breathing top end makes more power from the same boost, things run cooler, win win.
Good to hear there is progress..

 

I like vapor blasted finish better then paint, I'd leave it as is, but that's just me. BTW, I made and installed
aluminum motor mount bushings to help tighten up the chassis on my 750. Does anyone else here do that?
With the engine out it an easy modification and it works, I've done it on two on my bikes XJ750 and XS1100
Cheers, 50gary

 

my head is still the completely stock original.
The only mod I'm making is a bigger bore.
My biggest complaint with the OEM Seca Turbo was they were a complete dog below 6,000 rpm
Mine is already much lighter, I want 750 like power before boost.
I don't know enough to start hollowing out the ports.
I can't see that it would make much difference anyway.
When this thing hits boost I have no complaints.
A turbo becomes a matter of time.
How long are you going to hold the throttle open?
120 MPH comes up real fast.
Anyone else with a Seca Turbo knows the shot out of a cannon feeling.
When I was riding it at 16 psi it scared me that it was making so much power.
It felt like something had to break.
@Minimutly you mentioned earlier the turbo spinning up faster is a really good point.
If boost were to come on 1,000 rpm sooner then I would assume the taper on the main needle would need to be different.
What do you think of modifying tapers on main needles?
Sandpaper and a drill?
Thinking this would be easier than finding a Mikuni p/n that would work.

We need some pics @50gary
Did you drill your mounter mounts to accept bushings?

 

Hmm, porting a head takes some skill and knowledge, needs specialist tools, and is easy to do wrongly, and scrap a head.
That said, adding a turbo, and therefore more airflow to the 650 head (especially exhaust ports) is likely to restrict its efficiency to lower levels than the original engine - sort of three steps forward, one back.
Maybe it should be a job for further along the learning curve, you might find you feel it's not required...
As for modifying four needles identically, I used to do it with a file on one side of the needle, that way you can see the amount removed by the width of the flat created, but I've never done four of them. you likely will need bigger main jets too? Weak running turbo engines have a penchant for eating pistons, in about 6 seconds in my experience.

 

Simmy,

On the subject of Mikuni needles, having the original ones to compare to this chart may be helpful in determining what your options may be:
https://www.jetsrus.com/a_jets_by_carburetor_type/needle_mikuni.html

I will be a challenge to dial in the changes in jetting once you get it running and back out on the road. I would start with going up with the mains and that will hopefully keep you from leaning out at higher rpms and potentially burning a piston or two. Also, with the pilot jets, going up at least one size from stock may add a bit of insurance too.

I'm with you as far as the heads go, and feel porting could turn out to be way more of a risk than it's worth.

Tony

 

I scratch made aluminum bushings (gotta have a lathe) the size of the rubber ones with a slight shoulder to keep them from migrating.
I have the dimensions written down somewhere. Keep clearances tight for the most effect. They are simple parts and cheap to do. I'll look at them tomorrow.
Cheers, 50gary

 

That's the proper way of doing it; the only thing that would worry me is that fitting those hard bushings into the mounting ear on the engine block.....which is very thin on the diameter.....might result in a fracture on the casting (the rubber bushings absorb a lot of the stress/flex which the alum bushings won't, and thus transfer the stress to those thin "ears"). On bikes (Seca models, mainly) that don't have rubber-bushing mounting for the engine to the frame, the mounting ear is basically solid, with just a small "hole" (passage-bolt diameter, either M8 or M10) and that style mounting lug is a lot beefier than on the bushing-mounted bikes......

 

@chacal, what are your thoughts on using something like urethane such as the truck guys use for suspension bushings for the engine mounting bushings? Or maybe skate board wheels for their material? I have a 750 engine going into a 650RJ frame.
Sorry for the thread hijack @Simmy. I am enjoying your build thread greatly, thank you.

 

OK now I understand, stiffening up the Maxim rubber mounts.
Seca already solid bolts.

 

nice info, I have some reading now thanks.
Too bad the BS carbs are not in the listing.

 

Not to hijack the thread but here picture of the alu. motor mount bushing, click the thumbnail to enlarge.
Look closely.
Cheers, 50gary

 

I believe the #5 series is the group you will need to look at as far as choices that will be close to what you have stock.
The overall lengths do vary quite a bit though, and will need yours out to measure the existing ones as a baseline.

As backwards as it may seem, the upper rpm fueling should start with dialing in the mains first, then needles will be able to be dialed in for the midrange.

Tony

 

As backwards as it may seem, the upper rpm fueling should start with dialing in the mains first, then needles will be able to be dialed in for the midrange.

Tony[/QUOTE]
Indeed, correct. The main jet must be big enough to give you your maximum required fuel, you could faff around with needles in the mid range, get it right, then find it falling flat on its face at the top end - cue bigger mains and starting again at the needles.
Question is, how big do the mains need to be? I would be doing a lot of research....
And then guessing.

 

here's my 772 big bore kit.
This block will make the motor 1 mm shorter.
Unfortunately this adds 2 mm slack to the cam chain, fingers crossed that this can be taken up by the tensioner.
New 68.5 mm rings, fresh bore, he did skim the top surface to level out all the sleeves.
I had him shorten the sleeves 2 mm just to be sure the won't foul anything with the crank.
The material was removed from the bottom so he also grooved the edge around the sleeves for the big o-rings.

block drilled and tapped for the knock sensor.
If I was more anal I'd grind smooth the 853 and stamp in 772.

 

Nah... keep it on as a sleeper

 

Except a sleeper delivers more than advertised, LOL.
This advertises more cc's than actual, seriously no one is ever going to see it anyway.

I'm planning to set up a wide-band O2 sensor and controller so I'm currently trying to buy specific #1&2 Turbo head pipes on eBay.
I'll weld the bungs in place to mount the sensor so I can determine what my fuel air ratio is at any given RPM.
Yamaha provide test ports right at the bottom of the pipes but the sensor mfr specifically warns not to mount them there.
Any condensation or raw fuel on the sensor will screw the readings.
I don't expect this to be pretty, that's why I'm looking for sacrificial pipes just for testing purposes.

The Turbo has 127.5 main jets on 1&4 and 132.5 on 2&3 so that's why I'm testing both pairs.
Planning to get baseline data as a 650 turbo before installing the big bore kit.
There is debate whether this will make the carbs/engine run richer or leaner, my bike shop guy insists it will be richer.
The XJ750 has richer jetting than the XJ650 which defies his experience.
I have not found anything on the net to reference turbocharged blow-through carbs and installing a big bore.
I'm not aware of any other factory turbo with blow-through carbs, maybe there were WW2 fighter planes I don't know.
I'm learning lots.

 

Lotus Esprit turbo (Dellorto carbs), MG Metro turbo, MG Montego turbo (single SU), Renalt 5 turbo , Renault 18 (Solex). Loads more...
With your original carbs, bigger engine shifts more air - thing to watch out for is the slides don't hit stops too soon, this would be disastrous, but its so difficult to measure (I've spent hours trying to do it). Denser air creates more lift, so in theory as boost rises the slides will rise, reducing the (relative) vacuum at the jet, weakening the mix.
In truth I've no idea....

 

Wow thanks @Minimutly you guys on the other side of the pond saw a lot of cars we didn't.

can you explain more on this?
What I thought was a can of worms is starting to become an oil drum full of snakes.

 

If the spring is too weedy, the slide tops out and further engine demand is only pulling the fuel the needle and jet can provide with the available area of the annular around the needle as it sits in the jet, no more. This means that more air can't get the right amount of fuel and a weak mixture results.
Weak mixture, high speed, holey pistons.
In my messing around with the SU on the GS, I've had this at the back of my mind for years and it's something I try to avoid, in my farting around.
I've had an AFR gauge on the collector for a few years, and can't be certain of its veracity - it might be what you refer to above, the positioning isn't optimal, so I tend to err on the side of caution.
What I found in the past with another engine, that just before the piston holed the engine was going like a fecking rocket.

 

Whats the general consensus on shimming the needles up to get into the enrichment earlier? I'm not turbocharged (XJ750) but running into a lean out condition running #122 mains and #42 pilots. The issue is above 3/4 throttle it goes flat, drop it back and it pulls again. Floats are at spec and I balanced the carbs along with checking the valves which are on the tighter side of book spec.
Sorry to jump in like this but I saw the carburetor talk and wanted to ask.
Thanks Guys

 

With the slide topped out there shouldn't be further engine demand?
Unless the turbocharger continues ramming increasingly more air in?
My maximum boost 9psi is already achieved early, wastegate cracks probably 8,000 rpm and holds 9 psi to redline.
The fuel regulator will always hold fuel pressure 2.8 psi higher than boost.

What brand do you have? Is it just a gauge? I'm not sure what I really need yet.
The Innovate Motorsports LC-2 was recommended to me.
https://www.innovatemotorsports.com/wp/content/uploads/2022/05/LC-2_Manual.pdf
they sell add-ons you can data log AFR compared to RPM, gets expensive though

how do you know it is lean?

As @Dave in Ireland related, going slightly lean should not behave as you described.
When you say "drop it back it pulls again" are you talking about dropping the needles back or dropping the throttle back?

 

Sounds and feels lean over 3/4 throttle and on the edge of breakup until I drop the throttle back then it picks up and the exhaust is more even toned.

 

Well, yes, the engine will carry on running on a lean mix, to the point where it stops entirely.
My AFR is from Canada...one of these (since superceded) plus gauge.
https://www.14point7.com/products/spartan-lambda-controller-2

 

The slide is lifted by the vacuum under the bottom of the flat bit being fed to the top of it - yes I know, with the turbo there is no vacuum, but everything is relative, and the pressure diff across the diaphragm is this vacuum from the underneath compared to the turbo boost pressure seen at the inlet. The whole thing gives the needle a constant vacuum - CV, what you lot call constant velocity.
But, denser air gives more lift, so does this lift the slide higher? I don't know. If the slide goes all the way up the constant vacuum at the needle is lost, once this happens I suspect the mix will go rich, since the vacuum will increase at the jet, but all control is lost.

 

My AFR sensor and gauge showed up.
There is a blemish you can see on the gauge, I'm hoping this is just oil or something between the lens.
I bought extra bungs and plugs so I can move it between cylinders 1 and 2.
I have extra header pipes for #1&2 and need to install the bungs.
I plan to make another bracket to screw into the LH mirror mount to hold the boost and AFR gauges.
Maybe I'll look into a Go-Pro to film the tach and these 2 gauges in the same screen.
I want all this information while it's still a 650 Turbo.

 

I added some green to the forest.
I’ve been enjoying the bike as is, haven’t installed the O2 sensor yet.
The headlight quit working, the OEM fuse box finally gave out, when I tried bending the tab to clamp the fuse tighter it broke, so new fuse box next.

 

Damn that is one sharp lookin' machine! Love that color scheme.

 

Today I fixed the broken fuse box.
Below is how I restored the old Yamaha one.
I salvaged an old box from a Seca Turbo wiring harness I had hanging in my shed


I found these 4 way fuse blocks at an electronics discount store several years ago.


I cut the bottom out of the OEM fuse box and made a loose fit with the new block



make sure there is a gap all the way around for the epoxy to fill
screw it onto a board with wax paper in between



apply epoxy along the 4 seams and push the new block in place.
Smear some epoxy on the salvaged sticker identifying the 4 circuits and stick it back in place


when it dries, it will pull right off the wax paper and leaves a nice smooth surface on the bottom


Sydney says good job



re-soldered all the connections,
I like using old-school glass fuses but now I can use SAE standard size instead of the weird Japanese standard Yamaha used


keeping the standard appearance was important to me. There is nothing elsewhere on this entire wiring harness which does not look factory Yamaha

 

On the fuse box, since doing 2 fuse boxes like this I’ve since learned Chacal sells the OEM fuse clips that crimp onto the wires.
This is the best way to go, a crimp is more secure on a vibrating machine and it returns things to 100% original.
If I do another fuse box that’s what I will do

 

THATS A NICE UPGRADE. I prefer original, too.
Perfect

 

Question for you (and maybe @chacal) on head gaskets. The 750 I have has a head gasket that looks like it's from a 650 - it overhangs the 750 boore. The 750 pistons have a relief around the top that looks like its designed to avoid this overhanging gasket, so did Yamaha take a bit of a bodge and not change the gasket? Or has someone fitted a 650 gasket to my 750 engine? I suspect I know the answer but would like confirmation please? Can someone measure the 900 gasket for me please also?
I have a bunch of 650, turbo, 750 and even an 850 engine, so am in the mood for some modifying for better performance....

 

Gasket 68.5mm

 

XJ650 all:: 64.10mm ID for both the Turbo and normally-aspirated engines, but the design (and thus the gaskets) differ between NA non-yics, NA yics, and turbo models.

XJ700 air-cooled: 66.20mm ID
XJ750 air-cooled: 66.20mm ID
NOTE: XJ700-air and XJ750-air gaskets will interchange, but the 700's use a slightly thinner gasket

XJ900 RK/RL (853cc): 67.70mm ID
XJ900 F/N/FN (891cc): 68.25mm ID

 

My 750 gasket (used), measures 63.75mm, which looks awfully like a 650 gasket - (once crushed the "hole" diameter shrinks I guess. So someone fitted a 650 gasket to the 750...
At least the correct 750 gasket does not overhang the bore.
Much thanks.

 

You know what they say about "previous owners"...................

 

I have bungs installed in spare header pipes for cylinders 1 & 2.
I angled #1 15 degrees to the front and #2 45 degrees to make certain the sensor and wires clear the front wheel and the frame down tube

 

I bought these pipes off ebay from the same seller.
#1 pipe was perfect but#2 actually had 2 large holes in the outer wall my welder repaired you can see below.
The seller wrapped the pipe in cellophane which I never actually unwrapped.
If I bought these for a restoration I'd be supremely pissed.
But these are just tools now after all, didn't need the attention they got

 

Yamaha 16G-2 means #2 header pipe for Seca Turbo