Hi compression piston and destroking?

[sidwyz]

So I have found a piston that looks to be just right for my engine build,
problem is the price!!

http://www.powroll.com/P_HONDA_CRF150_02-05.htm

This is a High quality, lightweight forged piston with a nice dome to give me roughly the compression I am chasing.

Is $360NZ delivered pushing it a bit too far on cost for a single piston no rings or pin?

I have searched high and low for another piston that meets the criteria, 63-63.75mm, 15mm pin, 2 valve with a decent size dome for compression and come up with nothing much.

any one got any suggestions?


Also where would one send a crank to be destroked?

What sort of cost would you expect to destroke a crank?
It would also be a single cylinder crank.

[koba]

So I have found a piston that looks to be just right for my engine build,
problem is the price!!

http://www.powroll.com/P_HONDA_CRF150_02-05.htm

This is a High quality, lightweight forged piston with a nice dome to give me roughly the compression I am chasing.

Is $360NZ delivered pushing it a bit too far on cost for a single piston no rings or pin?

I have searched high and low for another piston that meets the criteria, 63-63.75mm, 15mm pin, 2 valve with a decent size dome for compression and come up with nothing.
any one got any suggestions?


Also where would one send a crank to be destroked?

What sort of cost would you expect to destroke a crank?
It would also be a single cylinder crank.

I can only offer two shitty suggestions as a sad attempt at humour:

1) Buy an FXR (Bet you have never heard that one before!)

2) I recently heard a story about a guy who tried using bog on top of pistons to raise the compression in his Cortina. No actual word on whether it worked or not...


speedpro knows about de-stroking a built up roller bearing crank. Not sure if your dirty diesel is the same deal. I think he said "Heat Treatments", I'm sure he will be along with better details sometime soon.

[speedpro]

It does seem a bit pricey just for the piston and clips. Consider that I got a new chrome bore cylinder complete with forged piston, rings, pin, clips, and gaskets from Taiwan for US$87.70 and a 3.5mm longer stroke crankshaft for US$122.80 + freight of US$43 it would seem worth your time doing some serious research for another source. The cylinder is a lot nicer looking casting than the original Yamaha as well and the piston "looks" good as gold. I have JE pistons in another bike so I know what a good piston "looks" like. So far so good.

One thing I would be careful of is pistons with big domes. The flame front can be lengthened excessively plus the increased surface area and weight can be a drawback as well. I've run big old 2 valve engines and the flat(ish) top pistons always went better, maybe a horse or two down at top but better everywhere else.

The other thing is that a decent 4-valve piston could be flycut to fit in a 2-valve engine. I've fitted GSXR1100 pistons into a CB360 and that went real good.

[speedpro]

Also where would one send a crank to be destroked?

I got my bits made at "Heat Treatments" here in Akl. I dummied up the pin I wanted then they made it and heat treated it.

What sort of cost would you expect to destroke a crank?

LOTS, and that's only if you dismantle the crank and reassemble it yourself

[sidwyz]

I can only offer two shitty suggestions as a sad attempt at humour:

1) Buy an FXR (Bet you have never heard that one before!)

2) I recently heard a story about a guy who tried using bog on top of pistons to raise the compression in his Cortina. No actual word on whether it worked or not...


speedpro knows about de-stroking a built up roller bearing crank. Not sure if your dirty diesel is the same deal. I think he said "Heat Treatments", I'm sure he will be along with better details sometime soon.

(1)Was thinking about a fxr briefly but after riding Dads Gl (modified and goes pretty well) have woken up, too many of them and its good to beat them on a old 2 valve.

(2) only a cortina owner would try something like that.

[sidwyz]

It does seem a bit pricey just for the piston and clips. Consider that I got a new chrome bore cylinder complete with forged piston, rings, pin, clips, and gaskets from Taiwan for US$87.70 and a 3.5mm longer stroke crankshaft for US$122.80 + freight of US$43 it would seem worth your time doing some serious research for another source. The cylinder is a lot nicer looking casting than the original Yamaha as well and the piston "looks" good as gold. I have JE pistons in another bike so I know what a good piston "looks" like. So far so good.

One thing I would be careful of is pistons with big domes. The flame front can be lengthened excessively plus the increased surface area and weight can be a drawback as well. I've run big old 2 valve engines and the flat(ish) top pistons always went better, maybe a horse or two down at top but better everywhere else.

The other thing is that a decent 4-valve piston could be flycut to fit in a 2-valve engine. I've fitted GSXR1100 pistons into a CB360 and that went real good.

I have looked at http://www.akunar.com/PRO_PISTONS.htm but am sceptical of the quality.

There is one there with a 6.25mm dome. it seems about 1.5mm higher than the std(.25 over) crf150f piston I have and about 2.5mm more than the standard gl145 piston, but short of measuring cc's ( I hav'nt bored the cylinder yet) to detirmine compression ratio it's all a gamble.

John Connor said to me go for all the compression you can get, you can always bring it down, it's a bit harder to raise it once the piston is chosen.

Could you elaborate a bit more on "The flame front can be lengthened excessively plus the increased surface area" for me please Mike, or refer me to somewhere to read up about it?

I will try to goolge about flycuting pistons, could be an option.

Thanks for your input much appreciate your knowledge.

[sidwyz]

I got my bits made at "Heat Treatments" here in Akl. I dummied up the pin I wanted then they made it and heat treated it.



LOTS, and that's only if you dismantle the crank and reassemble it yourself

This is for an engine my Dad is looking at building with short stroke and big bore, we were discussing this and thought it would cost moonbeams but not sure how many moonbeams!

[kel]

I run Akunar pistons, no problems thus far. From memory they have a good range of 15mm pin pistons, a high compression unit the FXR with its 16mm pin is far more difficult to find. Akunar also offer offset crank pins for destroking, or stroking depend which way you install them of course. I'll be placing an order with them in the new year so if you see something you want let me know.

[Grumph]

You do know XL185 is 63mm bore....and if you want to keep it all Honda, the 70cc single is 47.0 stroke....

A very short stroke 146cc.

[Henk]

I'm pretty sure someone (Richban?) tried the Akunar offset crank pin with messy and expensive results.

[koba]

offset crank pins for destroking, or stroking depend which way you install them of course.

Oh dear! it seems I totally mistakenly installed it backwards...

[sidwyz]

I run Akunar pistons, no problems thus far. From memory they have a good range of 15mm pin pistons, a high compression unit the FXR with its 16mm pin is far more difficult to find. Akunar also offer offset crank pins for destroking, or stroking depend which way you install them of course. I'll be placing an order with them in the new year so if you see something you want let me know.

sweet, I also am going to place an order for a few things, just waiting to see which way I am going piston wise.
will PM you 2moro about what your getting

[sidwyz]

You do know XL185 is 63mm bore....and if you want to keep it all Honda, the 70cc single is 47.0 stroke....

A very short stroke 146cc.

Yep have a used xl185 in .5 over unfortunatly it is a flat top piston and would end up with less compression so that a no go. cheers.
If you mean crf70 i think the stroke is only 41.4mm

[TZ350]

... unfortunatly it is a flat top piston and would end up with less compression ...

... I have searched high and low for another piston that meets the criteria, any one got any suggestions? ...

Sure its unfinished but this is how the gun BSA Gold Star tuners beef up the crank case and get a bit of compression and squish with a flat(ish) top piston it looks like there would be very little shrouding of the flame front unlike a domed high comp piston .....

Team ESE's interestes include 4-strokes .... and steam engines too ... true!

[Pumba]

I'm pretty sure someone (Richban?) tried the Akunar offset crank pin with messy and expensive results.

The off set crank pins were actually of good quality, but it was the pins split bearings that failed on Rich, twice.