Simmy's Naked Turbo Project

I'd be happy just doing the rings on my 750 SECA... spare change is a little low right now.

 

Is your 750 losing compression?
How many miles are on it?

 

You need to take inspiration from Alan Millyard and build an XJ straight-8!
How are your machining skills?

 

Don't remember the numbers offhand but they jumped a good 10 pounds when I added 10cc/cyl oil and puffed it again. Bike has 49,710 miles on the clock and it's taking a quart every few hundred miles, not quite enough to smoke but the huffing from the oil fill plug at idle is significant. Plan at some point is to ring it and do the valves along with a new timing chain, the ultimate goal is hitting 100K miles. I know a tool & die maker with some 70 years of experience who's willing to do the machine work so it's just a matter of gathering up the needed parts & gaskets then dragging the bike to my working area... which is a disaster zone at the moment.

 

Thankfully I don't have to play with the jugs on my Seca II...... but yours look great....... and jeez, Simmy, bigger is not always better, lol.

 

Really? Sez who?

 

The motor is all complete now.
I measured the valves before I tore it down and just measured them again. All in tolerance, taking the cams out shouldn’t change anything just good to verify.

 

I noticed that my base gasket was slightly oversized and thought about trimming it back without scratching the paint.
I took a close look and SONAMABITCH!
The gasket is torn right where it circles the oil passage.
I guess it wasn't perfectly in position, I didn't notice it.
There's an O-ring to seal the oil but I certainly don't like this.
Unless someone can convince me it won't leak (didn't think so) it's coming all apart again.
That's a lot of work.
Maybe I'll get a Turbo base gasket and enlarge the holes.
I used the cheapest 900 base gasket I found.
to my defense this gasket was too big on the outer dimension, it's overhanging a little at the other end to.
I think I can replace the top end in a matter of hours now that I just did it it will go fast but still, SONAMA?BITCH!!!!

 

I went back a few posts and there’s a pic of that base gasket before I put both dowels and O-rings in place. The gasket seems to fit pretty good. Just careless me at a major step. Oh well it’s a long winter here.

 

Dunno. I guess it comes down to ambition, personally I don't like the half-ass approach and would be lifting the top end up and replacing said gasket again knowing there's a reason for it in the first place. The other is I don't like oil leaks or any other leaks for that matter... top end would be coming up.

 

My OCD would get the best of me, lol. I'd have to swap out that gasket.... however, if it don't leak, it ain't broke??

 

I'm resigned to the reality of tearing it apart.

 

That sucks but it’s the way she goes sometimes

 

Probably done yourself a favour there, anyway. If that's a green Athena gasket, it would have compressed and squeezed out, meaning you'd have to replace it in a couple of thousand miles.

 

It was an Athena, I ordered an OEM Yamaha base gasket for a 31A and a Yamaha head gasket for the 58L

 

@Dan Gardner what brand is that head gasket you have?
It looks like it has a metal ring around the cylinder. I think the head gasket I had is also Athena and it was a monolithic material, probably not up to turbo use any way as @Dave in Ireland mentioned they’re crap.
The Turbo head gasket is all metal. I think I could scribe a 68.5 mm circle then just use a die grinder to make the bore. That would be the best gasket available. I bought an OEM 900 hd gasket in Australia pretty reasonable.
Base gasket was in France, also Yamaha

 

The XJ900 head gasket should be all-metal, perhaps as a 3-piece "sandwich" design......a lot of Yamaha head gaskets after the early 80's were of that design, whereas earlier gaskets were a fiber material with crimped metal "flame rings" (which is what is seen in Dan Gardner''s image). The 650 Turbo head gasket is all metal (but not the triple-layer "sandwich" design) and does not use flame rings (of course, the compression ratio of the turbo engine is much lower than of a natural-aspirated engine).

Would the 900 head gasket hold up to turbo pressures? Assuming the CR was reduced, I don't see why it wouldn't as long as you're running somewhere close to stock boost pressures.....would be an interesting experiment!

 

I will have stock 58L pistons and head gasket, 8.2:1 CR and 9 psi boost

 

What this could do with is a fully mapped ignition system, keeping the engine away from detonation risk whilst allowing higher CR and more timing off boost. Now, who was going to look into making one of these for the XJ?

 

@Simmy, as you are going to disassemble to replace the gasket anyway, is it worth the effort and cost to have the head or the block machined for copper o-rings as used to be found in the older high compression, racing engines I used to read about? I see the lower compression you posted above but the turbo pressure will be considerably higher. Just curious as I am not an engine builder of your caliper, more like an engine assembler at best.

 

You're not the first to suggest that. I'm keeping the boost to 9 psi and CR stock so I'm thinking it will be ok.