XT660 Tuning and durability - .: XT660.com

Snowman · # 1 26-05-13, 20:15

Im looking into buying a spare engine from a XT660Z and doing a rebuild of the engine and while the engine is apart upgrade it for some extra hp.

Ive seen that some people say that the stock barrel can be bored to 103mm but not more, but at the same time there are 104mm pistons on the market. Is it possible to bore and replate a stock cylinder to 104mm?

If you would like to do a proper build on a XT 660 engine, what would the modifications be?

Im thinking of bore and replating to 104mm piston, ported cylinder head, OTR cam, exhaust with better flow and improved airbox. What else is there that gives a bit more punch?

If i would do the things listed above, how would it affect the durability of the engine? How would the engine run compared to a 690? Would it just be a waste of money since im better off with a 690 from the begining?

Kev · # 2 27-05-13, 05:12

Quote:

Originally Posted by Snowman

Im looking into buying a spare engine from a XT660Z and doing a rebuild of the engine and while the engine is apart upgrade it for some extra hp.

Ive seen that some people say that the stock barrel can be bored to 103mm but not more, but at the same time there are 104mm pistons on the market. Is it possible to bore and replate a stock cylinder to 104mm?

If you would like to do a proper build on a XT 660 engine, what would the modifications be?

Im thinking of bore and replating to 104mm piston, ported cylinder head, OTR cam, exhaust with better flow and improved airbox. What else is there that gives a bit more punch?

If i would do the things listed above, how would it affect the durability of the engine? How would the engine run compared to a 690? Would it just be a waste of money since im better off with a 690 from the begining?

Been there done that, any engine performance modification will affect the long term reliability of a motor. The cylinder is to thin at 104mm & you may brake the cylinder skirt off with a 104mm.

Bore the casing & go as big as you want right up to 108mm.

A 105.5 bore with +2mm valves, 5050 cam stage 3 air filter will see around 76 rear wheel HP.

You can never compare the XT to a 690 KTM they are two different bikes, I am yet to see an XT anywhere the same weight of the KTM, we know we have the capability's of getting these motors up 125 rear HP as done on the 700 Raptors .

Snowman · # 3 27-05-13, 12:42

Quote:

Originally Posted by Kev

Been there done that, any engine performance modification will affect the long term reliability of a motor. The cylinder is to thin at 104mm & you may brake the cylinder skirt off with a 104mm.

Bore the casing & go as big as you want right up to 108mm.

A 105.5 bore with +2mm valves, 5050 cam stage 3 air filter will see around 76 rear wheel HP.

You can never compare the XT to a 690 KTM they are two different bikes, I am yet to see an XT anywhere the same weight of the KTM, we know we have the capability's of getting these motors up 125 rear HP as done on the 700 Raptors .

Well that it would affect long term reliability i fully understand. But my question would be more if i do those mods will i have to do a full rebuild every 10h or would i still be able to go for longer runs as the XT was built for.

Hum okey i guess im better off just buying a 690 then..

Kev · # 4 27-05-13, 13:36

Quote:

Originally Posted by Snowman

Well that it would affect long term reliability i fully understand. But my question would be more if i do those mods will i have to do a full rebuild every 10h or would i still be able to go for longer runs as the XT was built for.

Hum okey i guess im better off just buying a 690 then..

How long is a piece of string, both questions very hard to answer, I have seen a big bore XT's only do 1000kms before destroying the plating on the bore due to poor plating, I have seen big bore seize the small end pins at 3000kms, I have seen big bores do 7000kms then get piston slap, I have seen a big bore destroy its clutch within 200kms, I have seen big bores do over 10000kms with no problems, it all depends on what parts you use & the conditions the bike is ridden under, cheap parts don't last, longer piston skirts last longer, as you can see very hard to say how long yours would last.

All the above cases I have documented over time.

waynovetten · # 5 27-05-13, 21:24

Well I've agonised over buying a 690SMCR,more power and much lighter,the pro's and con's go on forever,I've got no problem with price and there's a steady stream of secondhand ones with all the bells and whistles.

Parts ain't cheap,secondhand spares are virtually nil so it's the expensive route at a dealer,assuming you have one local,but the deal breaker for me was the seating position,I could suppress every other doubt I had and that was quite a few,but the seating position!!!! I just couldn't get on with,if you do then it's worth a try,but I found them just impossible,which is a shame because they look the great.

Snowman · # 6 09-06-13, 11:50

Quote:

Originally Posted by waynovetten

Well I've agonised over buying a 690SMCR,more power and much lighter,the pro's and con's go on forever,I've got no problem with price and there's a steady stream of secondhand ones with all the bells and whistles.

Parts ain't cheap,secondhand spares are virtually nil so it's the expensive route at a dealer,assuming you have one local,but the deal breaker for me was the seating position,I could suppress every other doubt I had and that was quite a few,but the seating position!!!! I just couldn't get on with,if you do then it's worth a try,but I found them just impossible,which is a shame because they look the great.

Ive had a 690 Enduro before and loved the engine.

Actually here in Sweden i can get a hold of KTM parts for about half the price of Yamaha spareparts. So for me it would be cheaper owning a KTM in the long run if i want to buy some Yamaha/KTM spare parts.

Kev · # 7 09-06-13, 12:10

Most of my KTM 990 parts are cheaper than Yamaha parts here in Oz.

waynovetten · # 8 09-06-13, 12:45

Well you guys can speak as you find,but being the process of changing my XT around a little,I've just bought two tank side panels and mint seat for under �50,their are heaps of secondhand parts about.

Petenz · # 9 09-06-13, 13:10

I never do my motors.. I have found makeing the bike handle
you also make it faster... Cornering speeds faster so the stright line speed between the corners is faster also..
If its a dirt bike do the suspension it don't matter how much power you have , crap suspension can only put so much power on the ground.....

just about all stock standard bikes have more power than the standard
suspension & joe average rider can ever hope to make use of..

I have spent a small fortune on my XTR... but other than kev's 2 mods,
Rekluse auto clutch & a form air filter...not $1 on the motor.. and I bet on the trails it's
faster than most XTR's & it's still got more power than it "or me" can use..

Brutank · # 10 06-06-16, 10:16

Quote:

Originally Posted by Kev

Been there done that, any engine performance modification will affect the long term reliability of a motor. The cylinder is to thin at 104mm & you may brake the cylinder skirt off with a 104mm.

Bore the casing & go as big as you want right up to 108mm.

A 105.5 bore with +2mm valves, 5050 cam stage 3 air filter will see around 76 rear wheel HP.

You can never compare the XT to a 690 KTM they are two different bikes, I am yet to see an XT anywhere the same weight of the KTM, we know we have the capability's of getting these motors up 125 rear HP as done on the 700 Raptors .

Hello, I was looking at Boring my engine out in a few months as I have acquired a house with a garage. you say the Cylinder is too thing at 104mm, but then talk about a 105.5mm bore ? is 104mm their safe "limit" ?

As I would love to go around 105mm

Kind regards - Brutank

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