High compression pistons for 695

[suzyj]

With my suspension (showa) and brake (goldline) upgrades nearly done, I'm pondering the next bit of work.

I want to pull my heads and cylinders off to bead blast and repaint them at some point in the next n months, as the bike was running badly lean for it's first few years of life, so the paint on the cylinders and heads is an absolute mess.

So given that it'll be all apart, I got to thinking about what else I can do while I'm in there.  Higher compression pistons is an obvious one.  Only thing is, I can't find high compression pistons that are advertised as being for a 695.

My 695 uses 88mm pistons.  It's the same diameter as a 750.  Fast by Ferracci have a high compression piston kit for a 750, with a choice of 11:1 or 12:1 compression.  It's not even (all that) expensive, at $420...

Would it fit the 695?  I'm guessing no, as the OEM part numbers for pistons differ from the 750 to the 695 (122.2.004.1A for the 750, 122.2.149.1A for the 695)...

[2 Wheel Wanderer]

Off FBF's website for their 750 kit:

Requires cylinder boring and re-plating, which can be performed at Fast By Ferracci for $399 for both cylinders.

So total of $818.95, don't know if its worth it. I'm waitin till next year to make my decision.

[suzyj]

Sure you're not looking at a big bore kit?

I'm looking at http://www.ferracci.com/store/cart.php?m=product_detail&p=191, which makes no mention of boring or plating.

[He Man]

you still have to work out the fueling. so thats another $300 bucks for a power commander.
another $450 to reflash the ecu so you can get the full benefit of the power commander
and another $300 to tune it.

I'm the guy who thinks engine mods are useless unless youre going to OD on it. dont just do a bit here and there on a small motor that isn't going to give you much to begin with. BUT, if it makes you happy to do this mod then go for it, maybe you can pick up DS1000 heads on ebay....

[suzyj]

Now I'm confused.  I assumed that compression ratio wouldn't affect air/fuel ratio.  I mean, you get that same quantity of air, and the same quantity of fuel - you just compress both a little more...

[brad black]

the 695 has 4.3mm less stroke than the 750 with the same length rods, so the 750 pistons will be 2.15mm too short.  there's no piston that will go straight into it afaik.  you can get something made - Special Piston Services in Dandenong could do it.

or get some longer rods, you could even use 800 pistons then.

or fit a longer stroke crank.  800 crank will go straight in.

[2 Wheel Wanderer]

Sure you're not looking at a big bore kit?

I'm looking at http://www.ferracci.com/store/cart.php?m=product_detail&p=191, which makes no mention of boring or plating.

Yep, I was looking at the kit.

[suzyj]

or fit a longer stroke crank.  800 crank will go straight in.

Is stroking it really as easy as swapping the crank and pistons?  If so, that sounds like a very simple performance upgrade

[Raux]

it looks like i won't be using the 800 crank i had for the 696. it would fit your project.

you can use the 800cc 88mm HC pistons out there.

[motox79]

its a little more complicated than just "dropping" in a crank and pistons to make the motor an 800. Most cost effective way would be to just pick up a 800 motor and ECU and recoup some money by selling your motor/ecu.

[suzyj]

Hi Raux,

If you don't mind holding on to the crank for a few months (my marriage might not survive more bike expenditure at the mo), I'd like to take you up on that.

Motox:  There are complexities beyond just the cost of motors or parts as well.  Here in Australia, the cutoff between insurance bands is at 725cc.  So if I can keep my current 695cc engine number, but change the pistons/cylinders/crank to 800cc, then it's more cost effective than the raw numbers might otherwise indicate.  Indeed the most cost effective (in the long term) thing may be to buy an 800 motor, swap its pistons and crank over to my 695 motor, and then resell the 800 motor as a 695 in order to keep my engine number.

I studied the spare parts manuals for both bikes - the crankcase, conrod, and heads have the same part numbers, but the numbers for the pistons and crank differ.  The number for the cylinders is also different, though they only come with pistons ncluded, so whether the difference is just the pistons or is the cylinder as well remains to be seen.

In addition, the part numbers for belts and belt covers are the same - I'd have thought if the cylinders were different, then the belts and belt covers would also have to be different.

Of course installing a new crank necessitates dropping the whole engine and splitting crankcase halves, which is sure to be an enormous job (much bigger than just popping the heads off as I was planning), but it's really nice to know it's doable.

[Raux]

sure i won't throw it in the for sale section.

althought the 800 part swap sounds good, you would still have to go buy the HC pistons if you wanted to go that route.

[suzyj]

So I can find it easily later, here's a link to HC 800cc pistons.  http://ducshop.com/product_view.php?cat=6&pid=286

[brad black]

don't know where you'd find an 800 motor, especially out here.  none on ebay.  you'll need the crank, pistons and ecu.  not sure if the 695 vs 800 chamber size is the same.  it might have higher comp with std 800 pistons, but i'm sure they have the same valve sizes so chamber would have to be pretty similar.

splitting an engine isn't a big deal if you're game and have some experience.  depends how far you want to get into it.

are the 695 cylinders black?  the colour variation will also require a different part number.  they should be indentical tho i'd think otherwise.

[Raux]

what would be really cool for the change would be the 696 heads which flow better than the 695 heads. and i'm pretty certain the valves are larger as well.

but that is a good point. the ECU. the 696 ecu would require a reflash to the 800 and perhaps to the 800 dp with the hc and other changes. fortunately the 695 is the MM ecu and there are plenty of places to do that.