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.

 

It's taken me almost 2 months to acquire new gaskets. I bought a head gasket for the 4BB from Australia and received it in 2 weeks. A base gasket from France never did show. As soon as I said not received had refund in hours.
Finally found a 31A base gasket in Quebec which took about 1 week. It looks like a Yamaha number but can't be sure.
I'm hoping to start back into this again in another week or so.

 

I'm reminded of the days when Dad made gaskets from copper sheet by hand. He raced Sprint Cars with Hudson engines.

 

@k-moe, Wow, that is cool! Definitely a racing niche market, but very cool. Not something you hear everyday.

 

a productive Friday 13th,
I disassembled the block again to change the torn base gasket.
The Yamaha gasket was much more precise, still a caution to anyone assembling the block, those gaskets are very thin around the oil passages. New all metal Yamaha head gasket.
I got as far as torqueing the block, not bad for my 64 yo back.



torn Athena base gasket

replacement gasket


Genuine Yamaha head gasket for the 58L
The Athena head gasket I think was sold as compatible for the 31A or 58L so not a precise fit LOL

 

These wooden blocks were not my idea, I may have read about it on here.
The trick is to block 2 and 3 solid on the wood.
Then you just work the rings into the cylinders on alternating pistons but the trick is to lock the crank in place.
I stab the rings in place with a wooden chopstick

 

#1 shot right up to 150 psi, the pic shows the decay in pressure in the time to get my phone out.
#2 went over 140 before the battery gave out.
Its been a few months since the charger was on it.
This old guy did a big bore job in a weekend, started Friday finished Sunday.
It was the 2nd time around but really didn't take any less time.

 

I just popped the top of one carb to see what it takes to raise the needle.
Not sure if they are grooved
There is a plate securing it and the 2 small screws are really in there.
Task for another day.
I'm going to try starting the bike with stock jetting but I'd like to raise the needles.
With the turbo spooling up sooner I want more fuel sooner.
Thinking that will get me close.
I have the wideband O2 so this should be easy to see if it needs to be richer or leaner

 

Today I verified all 4 cylinders are pumping 150psi. I have no confidence in the accuracy of that number but they're all the same
And the main jet needle is grooved with the clip in the middle position.
There are 5 positions so I can raise it 2 grooves.

 

Tonight I finished raising all 4 needles as high as they go. Those clips are extremely small and easy to lose. I also reinstalled the fuel check valve I previously removed while diagnosing the fuel starvation problem I had. Finally diagnosed as restrictive fuel filter, anyway it will be nice not having to remember to manually shut the petcock.

 

It sure would be so very cool if you and this bike were at @Hogfiddle's CNYCC so we could drool over it and dream. Just saying......

 

Thanks @Fuller56 it's on my list, hopefully @hogfiddles continues hosting this get together. He's usually a week before the Canadian Vintage Motorcycle Rally. Retirement for me happens this May so there will be more time for everything.
I'm planning to have all 3 of my Seca's at the Vintage rally this year, June 19-21.
This year is dedicated to 2 strokes but the only one I have is an 04 KDX220. My BSA is gone so only vintage I have are the Secas
Any of you guys within a reasonable drive/ride should consider this event, biggest I'm aware of. I was sure disappointed in the mid-Ohio Vintage Days last year. That's just a minibike convention

 

What BSA did you have? I've got a 650 A10 from 1960.

 

I had a 67 441 Victor I built from parts.
Even the crankshaft was in bits. Virtually no 2 parts were assembled together and Norton parts were thrown into the mix to add to the challenge.

 

I have a conflict, but I'm hoping to get to the CVMG rally on the Sunday. Maybe I can ride the Seca II there........

 

Yes a mish-mash of parts can be a nightmare. I came across a bike like the one in the photo but walked away very quickly.

 

Sunday is no good @Rayzerman, probably 75% of the participants are gone already.
Go early Saturday morning and spend the entire day, better yet come Friday morning and set up a tent.

 

Agree with you, but the problem is, I'm away and can't get back until Saturday after dinner.

 

Ah, the good old days, of a bike in a box for a fiver.

 

I have a 1956 BSA A10, I've put that same front brake in it but with different forks

 

Yes, i think the A65 forks are better with that TLS set up. I've taken it off my bike now and fitted a standard brake which when used in conjunction with the rear stops the bike quite well.