| KDX250 Cylinder damaged [message #455034] |
Wed, 28 September 2005 22:22 |
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I Just bought a siezed 92 kdx250 and after stripping it down i've found
it was due to a broken up crank bearing. One of the transfer ports is
quite badly damaged (large chip out it). Does this mean look for a new
barrel or whats my options.
Thanks in advance
Greg
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| Re: KDX250 Cylinder damaged [message #455036 ] |
Thu, 29 September 2005 01:03 |
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Greg wrote:
> I Just bought a siezed 92 kdx250 and after stripping it down i've found
> it was due to a broken up crank bearing. One of the transfer ports is
> quite badly damaged (large chip out it). Does this mean look for a new
> barrel or whats my options.
I suppose that cylinder has an electroplated bore instead of a steel
sleeve, since you mentioned a chip out of the transfer port and I only
see ONE size piston and rings on www.partsfish.com.
You can go there and register and look to see what a new barrel would
cost, or look for a good used one on eBay, or google for shops that
specialize in repairing electoplated cylinders, if that's what you
have.
If you do have the electroplated cylinder you can NEVER use chrome
plated rings, you have to use the softer cast iron rings. I found that
out the hard way many years ago when Yamaha was the first company to
use electroplated cylinders on their TD-1 production road racers...
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| Re: KDX250 Cylinder damaged [message #455056 ] |
Thu, 29 September 2005 08:36 |
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The cylinder uses a plated bore, looks like its gonna cost me.
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| Re: KDX250 Cylinder damaged [message #455058 ] |
Thu, 29 September 2005 15:51 |
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Greg wrote:
> I Just bought a siezed 92 kdx250 and after stripping it down i've found
> it was due to a broken up crank bearing. One of the transfer ports is
> quite badly damaged (large chip out it). Does this mean look for a new
> barrel or whats my options.
I'd like to see a picture of the damaged area to guesstimate whether
you could use the cylinder as-is. You may not realize how piston rings
work.
Rings don't seal the hot gasses in the cylinder because of radial
spring tension. They seal the hot gasses in because some of the gasses
get into the groove behind the ring and push it outwards.
When the piston of your 2-stroke gets below the top edge of the exhaust
port on the downstroke, all of the pressure in the cylinder is suddenly
relieved and there is nothing left but the weak radial spring tension
of the rings to push them outward.
The ring tend to bulge out into the exhaust port, which is fairly wide
if it doesn't have a metal bridge between two halves of the same
exhaust port.
The rings bulging into the port is what makes the horrible metallic
clashing sound in an air-cooled 2-stroke engine, water-cooled cylinders
muffle the clashing sound.
There are wire pins in the piston ring grooves to keep the rings from
rotating and having one of the ring ends SNAG in the open exhaust port.
A snagged piston ring will break, maybe the engine will seize...
And the edges of the ports will have a slight chamfer to guide the
piston rings back toward their grooves in the piston.
But the transfer ports are a lot smaller and narrower and they will
usually have metal "bridges" between them to keep the rings from
bulging into those ports. As I said above, the only pressure of the
piston ring against the cylinder wall and port will be radial spring
tension, the ring isn't pushing hard at that point.
Once the chrome plating has begun to be peeled away, more of it could
come off, disastrously, causing another piston seizure. Or, the damaged
area could conceivably cause piston ring snagging and subsequent
breakage.
Or, maybe nothing further would happen, due to the lack of piston ring
pressure in that area.
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| Re: KDX250 Cylinder damaged [message #455068 ] |
Thu, 29 September 2005 17:55 |
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Greg wrote:
> The cylinder uses a plated bore, looks like its gonna cost me.
>
It's 13 years old so you probably figured it was due for major service
anyway. Way I look at expenses now that I am older is one rebuild and
some precautions like changing the oil and using air filters means it
will last me the rest of my life.<grin>
As long as you are going through the exercise you may want to look into
porting. I've ridden a KDX before, have two in my driveway now I am
storing for my Son-in-law, they are good but not what I would call high
performance.
You may get lucky and find the damage to the port is material that would
be removed anyway during the porting process.
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| Re: KDX250 Cylinder damaged [message #455073 ] |
Thu, 29 September 2005 20:06 |
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Cheers for the replies, I'll try and get a pic of the barrel. Is it
possible to get the cylinder bored and a sleeve fitted perhaps.
Greg
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| Re: KDX250 Cylinder damaged [message #455080 ] |
Thu, 29 September 2005 22:23 |
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Greg wrote:
> Cheers for the replies, I'll try and get a pic of the barrel. Is it
> possible to get the cylinder bored and a sleeve fitted perhaps.
It would be fairly simple to bore out a 4-stroke cylinder and install a
plain sleeve, but how do you get a 2-stroke's intake, exhaust, and
expecially the transfer port holes with their critical angles cut in
the right places after pressing the sleeve in? It sounds like somebody
would have to be sleeving a lot of KDX's to make it worthwhile to
machine a whole bunch of pre-ported sleeves.
But, what do I know? Maybe there is a specialist out there who's doing
exactly that. What does google have to say?
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| Re: KDX250 Cylinder damaged [message #455081 ] |
Thu, 29 September 2005 22:36 |
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"Greg" <greg_milne [at] btinternet.com> wrote in message
news:1127975810.773457.227370 [at] z14g2000cwz.googlegroups.com...
> The cylinder uses a plated bore, looks like its gonna cost me.
>
Try here http://www.ericgorr.com/
If he can't fix it, he knows who can.
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| Re: KDX250 Cylinder damaged [message #455099 ] |
Fri, 30 September 2005 06:48 |
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krusty kritter wrote:
> It would be fairly simple to bore out a 4-stroke cylinder and install a
> plain sleeve, but how do you get a 2-stroke's intake, exhaust, and
> expecially the transfer port holes with their critical angles cut in
> the right places after pressing the sleeve in? It sounds like somebody
> would have to be sleeving a lot of KDX's to make it worthwhile to
> machine a whole bunch of pre-ported sleeves.
>
> But, what do I know? Maybe there is a specialist out there who's doing
> exactly that. What does google have to say?
Repair sleeves for ported two cycle engines have been readily available
for over 30 years- L.A.Sleeve
and other companies make them and they are available from any
motorcycle dealer. The ports
aren't exact out of the box but a good installer will match them with a
90 degree cable driven porting
tool such as is available from CC Specialties. Yes, transfer port
angles are very critical and there are
installers out there who don't take the time to properly match them.
This and poor sleeve to cylinder
fit have contributed to lots of cobbled up sleeve jobs over the years
and have turned lots of people's
opinions against sleeves. A properly installed sleeve will perform just
as well as a replated cylinder
and there are oversize pistons available for many bikes that came with a
plated bore.
Krusty, I'm surprised that you didn't know the 2 cycle sleeves were
available.
Jerry
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