Upgrade to Bigbore Pistons

zukdave wrote: As to what size you need to take the cylinder block off the motor and take it to a machine shop and have it checked
before buying pistons.

The block is delivered to engine workshop, waiting for feedback from him on size.

For what it's worth... I bored my extra 1977 KZ1000A cylinder block out to accept the Wiseco 1075cc 10.25:1 pistons.
And I put that configuration back together with a fresh valve job head.
Even though I have a brand new solid state ignition, I am even still running the stock points system.... it just runs that good.
The only thing I needed to do was is slightly enrichen the fuel metering in the VM26ss carbs.... and I mean slightly.
One up on the main jet and I moved the needle clip one groove, I think my pilot jet is still standard.
That's really it.
NO OVERHEAT issues at all and, I do not have an oil cooler installed.

I can't tell you what the extra power from stock was because the entire bike felt different after that.
Noticeably more low rpm and midrange rpm torque.
I mean two up riding, (wife and I).... amazingly to me, I can run in 4th gear at 2000 rpm on the flat roads.
at 3200rpm in 5th gear I do not really need to down shift to pass slower traffic on the hiway either.
I am using a 2 tooth larger rear sprocket though.
But my fuel mileage actually went up a bit from the year before!!
I'm sure bigger 28mm carbs, with a bit richer mix would make more power but I'm very happy with it as is.
On a 650 mile trip up and down the Rockies last season, I averaged around 50mpg to 54mpg. Which I thought was pretty good and the engine pulls like a freight train through the mountain passes.

I think because the old engine was just a little tired and the valve job with new rings and better compression, those things just made more of a difference then the 2mm over bore, ore 60cc increase.
I think you might find that to be the case too if you go full top end overhaul.

Now.... on an old 3 cylinder 740cc Triumph Trident of mine.... I found that it was time to a top end overhaul.
I couldn't fine many options for that engine and overly anxious.....but I did find a set of 12:1 (yes 12:1...LOL) Hepolite piston kit.
But it was also 2mm over bore. Making the cylinders unusable for any future new re-bores.
So, stupidly, I did it anyhow including, lapped the valves in and installed some shims under the valve springs.
That pushed the 740cc, 58HP engine up to a whopping 785cc.... or, 45cc bigger..... but it was a stinker-bugger to tune with those AMAL carbs, crummy three points, three coil ignition system and that much compression.
And it ran hotter then Hell, especially in the center cylinder. I also had a three into one Jardine header on that one.
But hot, really hot.
Even after using two oil coolers, the center cylinder running a full step richer in every metering circuit then the outer two... HOT, and eventually causing me to re-ring the center cylinder after only 3200 miles.
The difference in power on that one? A bit.
Added: Memory not so good....
I actually dyno'ed that one after (not before) and it made 61HP at the rear tire after the engine rebuild and header install. more power over dead stock when but cool and quiet.
I don't know what the real HP was at the rear wheel stock.... maybe 50HP-52HP?

I just looked at my old journal and it was 61HP at the rear wheel after mods.
Also just noticeable. but what a pain in the butt to keep it going.
Plus, I had to run a mix of 100 Octane aviation fuel with +90 octane car gas.
I would frequently not ride on 85-90 degree days.

Then one day my buddy bought a 903cc 1974 Z1.... when I got to ride it, HOLY HELL, one too many times, I knew I could not own the 71' Trident much longer
Although I'd sure like to have an old 1971 T150 Trident again, for old times sake!!

So the point... sometimes it's just better to buy a bigger bike! LOL
Sorry for the rambling....

If you install big bore pistons like these in my engine, its only jetting you need to do, understand, 99% sure here ?

1.
I have original ignition... that is not a problem ?
See attached picture of ignition module.

2.
My bike is a original 81 650 SR European model, where the engine has been replaced with a 750 engine.
What is the difference between a 650 SR and 750 version when it comes to technical?
brakes ? frame ? etc.. reason I`m asking these questions is to looking into getting the 750 engine approved in the papers against the authority.

No eBay APP ID and/or Cert ID defined in Kunena configurationI have now purchased bigbore kit


Looking forward to test it

That's awfully big. Could run really hot.
Steve

Took another look at it. One or all four? If it's 810, that'll give you a kick in the pants.:woohoo:
Steve

Can the stock sleeves take that overbore?
I don’t know.
I think my stock sleeved 1015cc block is maxed out at 1075cc.

I think we can go 1105.
www.z1enterprises.com/catalogsearch/result/?cat=&q=73.0+sleeves
If it's a 750 I'd think 810 is the max. My question for both is if there are one or two oversize's in case of piston failure.
Steve

Hem... have I done some stupid?

I overhaul almost my whole bike and want a bike I can trust (starting when I need it), I can have short and long trip and don`t need to be afrid someting goes wrong.....

+0.25mm VS +3.00mm .....

From what all you have replay to me will the overbore set to 810 give me more nm and not peak power.
Normal I only need to-do small re-jetting and nothing else, use original ignition and keep the rest of the engine original,
the valve will be overhauled.

Things I need to be aware of is over heating or hard throttling....

Normal I run the bike nice and are not hard to it, I don`t run to the limit, but its nice to have some extra power available when you need to overtake a car etc in a hill.

I can add I`m living in Norway and a normal summer is between 59-77 degrees Fahrenheit.

How can I avoid overheat? have a eye on the temp and run it nice when its hot?
I was thinking replace the oil filling cap with a temperature meter?

If I got problem with heat I can install oil cooler ? but it shall not be necessary?

I will not be able to re boor the cylinder? so It will be nice to get a spare barrel to have just in case?

But I understand I can expect these setup shall work for almost the same time as original stock pistons, I take care of the engine?

What about the brakes and the frame construction? My frame is a 650 SR European model with disc brake front (double) and single disc brake rear, I have understand my bike is identical to a 750 when it comes to brakes / frames / etc.. so the bike itself
shall handle 750 stock engine, since Kawa using the same part for 750?

If the jetting is correct you will not have over heating issue's with that piston kit.
At one time Wiseco made an 830 cc kit and they had over heating issue's on the street.

Why would a big bore piston engine run hotter than a regular engine if both were going down the road at the same speed? I understand that the big bore engine will have more potential for power, but if the rider is keeping the same speed, thus the same power being generated (big bore engine can get by with a smaller throttle setting), there shouldn't be much if any difference in heat unless I'm missing something.

Glad to see you went with the 810 and the better quality Wiesco's. I kick myself almost every day for not going that way when I re did mine...... Even have a 750 block but was too chicken to open up the cases to have them bored (you don't need to with the 750 motor). With your cooler weather I wouldn't worry a bit on over heating....... out west its like a oven and Zukdave and many others are doing fine.