Big Bore Kit

[Michael]

Hi guys,

I am currently working on a big bore kit to 865cm³ which equals to 84mm bore and 15% more volume.

In addition the calculation and production of new intake camshafts is under consideration.

New bearing shells for crankshaft and push-rods are asked for, as well.

Any interest from your side ?

Cheers, Michael

[Kaptainkwak]

Big bore is interesting but need to know cost. I think I know the cam mod. Are you looking at standard size shells?

Cheers

KK

[Michael]

Hi KK,

will dismantle the engine of “Back in Black” to hand it over in pieces as the example engine, where stock dimensions can be taken, etc.

We will determine the possibilities, describe the content and will find a price.

Looking to get the bearing shells in all three original used sizes.

We will see and it will take several weeks before further and final results will show up !

Cheers, Michael

[jett]

Hi, Has there been any advance on this Big Bore kit. I am extremely interested if one has been developed.
Also, could you please let me know where i can purchase the oil temp gauge that is pictured on your engine?
cheers,
jett

[Kaptainkwak]

Hi Jett

There have been various Big Bore projects, some of which have been successful. 865cc has been achieved here in the UK and also Germany I believe.

Michael from Germany German 750 twin Website has been working on a 920cc? big bore. I am sure he will be along soon to comment.

I also believe someone attempted over 1000cc but this took quite a lot of extra work and wasn’t totally successful. I have also had suggestion on achieving 942cc using pistons from a Yamaha FX sho 1800 wave runner. Apparently the stroke is the same but the Yamaha pistion pin is 21mm dia which may cause an issue as our twins use a 19mm pin. This is as far as I heard with that one.

Cheers

KK

[Michael]

Hi Jett,

this engine is still under development.
It caused me a lot of trouble to get a big bore kit as a small series production and I refused to push that.
This is a one-of-it’s-kind production.

I know the supplier, who is not the manufacturer and may ask if he can have another one made. Price without shipping will be in the range of 1.200 to 1.500,- Euros for cylinder with wider sleeves, larger pistons, bolts and rings. All ready to “bolt on”.
No head gasket included, needs to be made from copper sheet metal.

Currently I am out of money as I have to move from one house to another.

Some thousands of Euros have to be spent for that move and it has priority.

I am going to order reworked camshafts and to get the combustion chamber adjusted to match the bigger bore. After that I will reassamble the engine with the best parts that I have available.

Camshafts can be done by Megacycles in the USA. I have found a company in Germany called Campro who offers that as well.

Find a report with some detailed information about a 950 cm³ engine:
http://translate.google.com/translate?sl=de&tl=en&js=n&prev=_t&hl=en&ie=UTF-8&eotf=1&u=http%3A%2F%2Fwww.z750twin.de%2F

865cm³ is a good size.
With my 906cm³ set I expect it to be the largest size without opening the “tube” of the innermost cylinder mounting stud to the sleeve.
With 950cm it needs very careful maschining not to damage the material.
I have seen an engine and I was told it has 1000 cm³, but it was necessary to change the complete oil circuit to the camshafts by using external oil lines.

Can help with some translation but not before next weekend.

Ducati pistons of some dedicated and listed models are the key.

Cheers, Michael

[Michael]

Oh well,
all above listed displacements are avieved with stock stroke of 78 mm.

There is an engine in Germany existing that has a longer stroke and I know the owner (Martin). This engine is not in use !
May ask about the status.

… and just for the fun of it:
This engine doesn’t work, it was a mock-up during my big-bore conversion:

[Michael]

Ah, the oil thermometer.
It has a very short dip stick not to collide with the primary chain.
Measuring accuracy is not very good but it indicates the engine temp.

Not sure about the thread size, but here is a list of the available versions:
http://www.polo-motorrad.com/en/oltemperaturmessstab.html

Polo is a large german discounter with a lot of shops around.

Cheers, Michael

[jett]

wow, thank you so much Michael and KK!
I have a K engine in a crate that is in lovely condition and my plan was to get it professionally rebuilt and i figured i might as well get it bored in the process.
Is 865 a safe capacity to take it out to? Reliability is still a high priority for me.
Cheers, jett

PS Thanks Michael for the heads up on the oil thermometer. What sort of engine temperature should i be expecting?

[Michael]

Hi Jett,

865cm³ looks to be a very good size to achive still long lasting operation.
Martin’s engine with 865cm³ has, I don’t know exactly, something between 20.000 to 50.000 km on it. A lot of stuff, that’s for sure.
That is max size without any impact to other “components” or minimum material thickness of them in the engine.

My thermometer shows a max. of 80°C, even with fully “heated” engine.
I expect the real value to be around 100°C.
Despite of the measuring accuracy and the sub-optimal position of the dip stick it will indicate if the engine is still to cold or if it is warmed up enough to use max. power (FOT) 😉

Cheers, Michael

[jett]

Please excuse my ignorance about engines, but is there an 865 kit that i can buy (or a list of high quality pieces that i can assemble) and then take to a engine builder here in Australia and have them do the work?
Apologies for the endless questions. Thank you for being so generous with your time.

[Kaptainkwak]

The 865 big bores have been done by 2 guys who I believe shared their information and knowledge. They don’t come in kits but if you give me time I will try and get the information needed for you.

Don’t apologise at all just keep asking away

KK

[freefaller]

I’m very interested in the bigger bore options as well. Thanks for any info.

[Author]

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