Topic: CB 836cc f1 turbo - spoked kickstart street turbo

[Ilja]

Just did the frame cut.... I must say id rather not but with an experimental engine you really dont want to lift the complete engine everytime.
The bottom tubes both jumped 1mm down after cutting so thats a little pre-tension going out.
I can see the cutted tubes move by twisting the frame by pushing on the handlebar and pulling the rear frame.. so this piece of frame is definitly needed there!

I'll bolt it back with the weldless frame kit. Frank, your a life/spine-savior!

[Ilja]

Well looks like the large squish band pinging theorie was correct.

[Ilja]

Cylinders are fine thank god.
2 pistons have the ringlands cracked.
Classic turbo detonation failure.

[Ilja]

Or I might go forged ones... 

[Ilja]

So.. I had a +4mm bore due to the bigbore kit and a 2.5mm high squish band.
I just compared with the stock pistons, almost no squish band at all..
So I'm wondering if I should keep the squish band and make it tight 1.25mm... or just cut it out completely like stock...

Does anyone know what the bigbore sohc's typically do after going to 900 or 1000cc?

[Ilja]

Well.... got another surprise.
When I build the engine I kinda assumed the engine to have stock CR... 9.2:1.
I calculated at the time that if I would add 1mm spacer, taking into account the 836cc kit, I would end up at 8.2:1..
BUT assumptions are the mother of all f*ckups..
I just measured the heads combustion chambers, deck height, compressed base+head gasket thickness and the piston domes(flattop but slightly domed).
My measurements:
-Chamber: 21cc
-65mm bore
-63mm stroke
-Piston dome of 1.5mm = 3.3cc
-Piston to deck height = 0.8mm

If I calculate correctly this gives a compression ratio of...... 9.5:1  oops..
I bet it would also save me some pings if it were 1.5 point lower... 

[TurboD]

What are your ring end gaps? I have seen far too many ring lands broken from tight end gaps, and most of the time the blame is placed on something else.

[Ilja]

What are your ring end gaps? I have seen far too many ring lands broken from tight end gaps, and most of the time the blame is placed on something else.

I have checked and set them on the wide side of the specified range. Should be ok.
One piston had the ring lands pinched together and one piston had broken ringlands. The other 2 are ok.

[Ilja]

Small calculation:

Effective CR = SqrRt(boost+14.7)/14.7)*CR

So, running 8psi (it started to ping above 8psi) and 9.5 CR gives:
SqRt((8+14.7)/14.7)*(9.5/1) = 11.8:1 Effective CR.

12:1 CR (or ECR for boosted applications) is around the max you can run on pump gas, so its not so strange it started to ping above 8psi or 0.5bar.

It kinda broke down when I was running at 11psi, with boost spikes of 14psi in midrange. Audible pinging.
SqRt((11+14.7)/14.7)*(9.5/1) = 12.6:1 Effective CR. 

If I recalculate using 8:1 CR:
SqRt((15+14.7)/14.7)*(8/1) = 11.37 Effective CR. So 15 psi or 1 Bar should be ok if you run 8:1 CR.

My kawasaki turbo is at 7.8:1 CR, and I sometimes run 20psi w/o problems so far.
SqRt((20+14.7)/14.7)*(7.8/1) = 11.98:1 ECR.... right on the edge!

[754]

Cut or measure a damaged piston, to see how my uch you can carve out of the top...

[Ilja]

Ohh, good idea!
Might be needed because I don't know if I can take enough out of the heads combustion chamber..

An F2 head would be helpfull now. 

[Ilja]

Allright, ordered new parts and received everything except the MLS headgasket.

Just measured the primary chain slack and they are at 72mm sag..  engine was already rattling when I bought it.
New Audi HD ones are going back in.

[Ilja]

Well... theres good news and bad news.

-Crank and conrods are fine. One crank main shell looks a bit scratched but not too bad.
-Axial bearing surfaces of the engine cases are a little worn. The crank just runs against it with a machined ridge, so not much I can do.
-Output shaft and gearbox and everything, all fine.
-Primary chains have stretched a lot. I could really lift the chain a lot from the cush hub. I've added a picture comparing old to new (HD Audi chains)
-Cush hub sprocket teeth are a little worn, but not much I can do about it.

So now for the bad...
One of the m8 casing bolts in the middle of the casing on the bottom side, where the crank is held, had to say SNAP.
And the piece that's inside sits in a pothole.
So this will be tricky getting it out.... I hate this.

Might just take it to a machine shop and let them put it under a mill and machine it out. Perhaps if necessary putting a helicoil back in.

[ivanhoew]

oh pooh ,don't you just hate snapped off bolts.

[Ilja]

Lol, check out this funny but interesting vid of some guy removing a broken off bolt with "alum".

Never seen it before, but could try it if I cant drill it out.. 

[Bootsey]

Lol, check out this funny but interesting vid of some guy removing a broken off bolt with "alum".

Never seen it before, but could try it if I cant drill it out.. 

That's rather impressive if it really happens to work that well. The commentary in the video was quite entertaining too, haha.
Good luck with the broken bolt.

[Ilja]

Allright, this weekend I will try to get the broken stud out... fingers crossed! Got most of the parts in to put the engine back togheter.

I found that the two small bearings on the primary shaft are feeling grindy when turning, so gonna replace those.
The rest of the engine is fine! Clutch, output shaft & bearings etc...

What do you guys think about the two needle bearings and the dampers in the primary hub?
I think I will do the needle bearings, but the dampers seem fine... although 39 years old.

And the thrust bearing faces of the crank, did anyone else experience this wear that I got on the engine casings?

[Ilja]

Yay succes!

[scottly]

What are your ring end gaps? I have seen far too many ring lands broken from tight end gaps, and most of the time the blame is placed on something else.

I have checked and set them on the wide side of the specified range. Should be ok.
One piston had the ring lands pinched together and one piston had broken ringlands. The other 2 are ok.

The wide side of the range for NA may be too small for large amounts of boost.

[Ilja]

What are your ring end gaps? I have seen far too many ring lands broken from tight end gaps, and most of the time the blame is placed on something else.

I have checked and set them on the wide side of the specified range. Should be ok.
One piston had the ring lands pinched together and one piston had broken ringlands. The other 2 are ok.

The wide side of the range for NA may be too small for large amounts of boost.

I'll do a compare with my gpz turbo factory specs and double check!

[Ilja]

Primary tensioner old vs new.
New is really soft!

[Ilja]

Shortening primary chains...
Pins go out w/o damage with just a few taps with a small hammer.

The old chains stretched to around 1 link extra!!

[scottly]

Are the GPZ rings of similar diameter and thickness? What sort of clearance were you using?

[Ilja]

Are the GPZ rings of similar diameter and thickness? What sort of clearance were you using?

If I remember correctly I set the ring end gap at 0.3 or 0.4 mm.
Just checked the kawasaki 750 turbo ring end gap specs and they specify between 0.2 and 0.4mm with a service limit of 0.7.. identical to the N/A version.
Pistons are also cast, almost same diameter and rings also more or less the same.
Should be fine!

The engine lived for 1500km's including hours on the highway. As soon as I upped the boost and I heard the detonation ticks within 10 km it pinched a ring tight between the ringlands and blew oil out of the breather.

[scottly]

How much boost does the stock Kawi 750 turbo make? 5-7 PSI? Sorry if it seems like I'm flogging a dead horse.