The SCARR Husqvarna 592XP build thread.

[wcorey]

The transfer runners look similar to a 461. What is gained by having the runners mate with the case at the front of the cylinder instead of on the sides as usual?

461 uses delayed scavenging while 590 uses stratified scavenging.
Two different methods to the same end result of lowering emissions and both require the long tunnels to get there.
Delayed uses port timing to facilitate a bit of reversion of exhaust gases into the tunnels while strato uses fresh air from a separated intake stream. So when the transfers initially open, previously combusted mix or plain air respectively is lost out of the exhaust as opposed to unburnt mix.

 

[ferris]

So we need some valves to get a more effective engine. And to limit the loses… Who will build some?

 

[Joakim S]

Sorry guys, I know this is going very slow. I went to cut the squish and bases tonight but found the cylinders too large to bolt to my normal squish cutting plate so I had to make a new one. I'll also have to make a 53mm mandrel to cut the base of the 585, at least I have a 55mm one for the 592.

I've been thinking about, if it's possible to use the same mandrel for 2 different cylinders, let's say like in your case, 53mm in one end, and 55mm in the other. Or is is something I haven't thought of?

 

[srcarr52]

I've been thinking about, if it's possible to use the same mandrel for 2 different cylinders, let's say like in your case, 53mm in one end, and 55mm in the other. Or is is something I haven't thought of?

Some people do that but I prefer to have the cylinder as close to the chuck as possible and I don't like clamping on the machined surface that will have to then slide into a cylinder. So I make mandrels for every size.

 

[srcarr52]

Some people do that but I prefer to have the cylinder as close to the chuck as possible and I don't like clamping on the machined surface that will have to then slide into a cylinder. So I make mandrels for every size.

Each one starts as a 6" long chunk of 6061 aluminum.

 

[Joakim S]

Some people do that but I prefer to have the cylinder as close to the chuck as possible and I don't like clamping on the machined surface that will have to then slide into a cylinder. So I make mandrels for every size.

Ok. Sounds right. Thanks.

 

[Joakim S]

Each one starts as a 6" long chunk of 6061 aluminum.

Ok. Do you have any experience of using POM for this kind of work. Sorry for going OT.

 

[srcarr52]

Ok. Do you have any experience of using POM for this kind of work. Sorry for going OT.

No, I've always wanted the rigidity of aluminum, acetal is easy to machine but lacks the rigidity and it about the same price as buying drop chuck of AL off eBay.

 

[Joakim S]

No, I've always wanted the rigidity of aluminum, acetal is easy to machine but lacks the rigidity and it about the same price as buying drop chuck of AL off eBay.

Ok. Good to know. Yes, I've seen on Ebay that the alu prices isn't to bad.

 

[Sleeper]

So we need some valves to get a more effective engine. And to limit the loses… Who will build some?

Sleeve valve, ftw. Make a 60cc saw run like a 90cc saw.

 

[srcarr52]

Since there was some questions on mandrels for cutting the base I figured I'd go over how I like to make them.

This is for the 53mm bore (2.085") so I started with a 6" long 2.25" diameter chunk of 6061 T6 aluminum. I cut the end flush and skim cut the surface where it will ride in the 3 jaw for the rest of it's life. I do this so I know I'm clamping on a concentric, flat surface as the raw material surface can be out of round and not exactly flat. I also put a healthy radius on the back edge to keep it from getting caught up in the chuck when clamping and prevents getting a raised edge from misshandling.



Then I flip that around and chuck it up, give it a good wiggle as you tighten the jaws so it seats in as true as possible. Then mark jaw #1 so I always put it back in the chuck the same way. Since I have my lathe, jaws and mandrel all marked I'm able to chuck the mandrels back in and bump them out to practically 0 runout across the whole surface.



Then I cut to the bore size -0.0005", don't forget to let it cool back down to room temp before your final few cuts. Then I under cut it so you can cut the base or skirt extension all the way to the bore, usually around 0.2" diameter will be enough. I also like to machine the end with a 1/4-20 center tapped hole and a slight recess.



That's because I like to put some 80-100 grit sand paper on the end for traction. With the paper I've been able to take 0.02" cuts on the base, but not on a large diameter, interrupted cut like these 585/592 cylinders... I'll stay below 0.015" cuts.

The sand paper also works great to clean up a squish band, remove some debris damage or just check how flat one is by the witness marks.

 

[Dolkitafreak]

Since there was some questions on mandrels for cutting the base I figured I'd go over how I like to make them.

This is for the 53mm bore (2.085") so I started with a 6" long 2.25" diameter chunk of 6061 T6 aluminum. I cut the end flush and skim cut the surface where it will ride in the 3 jaw for the rest of it's life. I do this so I know I'm clamping on a concentric, flat surface as the raw material surface can be out of round and not exactly flat. I also put a healthy radius on the back edge to keep it from getting caught up in the chuck when clamping and prevents getting a raised edge from misshandling.

View attachment 318243

Then I flip that around and chuck it up, give it a good wiggle as you tighten the jaws so it seats in as true as possible. Then mark jaw #1 so I always put it back in the chuck the same way. Since I have my lathe, jaws and mandrel all marked I'm able to chuck the mandrels back in and bump them out to practically 0 runout across the whole surface.

View attachment 318244

Then I cut to the bore size -0.0005", don't forget to let it cool back down to room temp before your final few cuts. Then I under cut it so you can cut the base or skirt extension all the way to the bore, usually around 0.2" diameter will be enough. I also like to machine the end with a 1/4-20 center tapped hole and a slight recess.

View attachment 318245

That's because I like to put some 80-100 grit sand paper on the end for traction. With the paper I've been able to take 0.02" cuts on the base, but not on a large diameter, interrupted cut like these 585/592 cylinders... I'll stay below 0.015" cuts.

The sand paper also works great to clean up a squish band, remove some debris damage or just check how flat one is by the witness marks.

View attachment 318246

Belt sander seems faster, just sayin’.

When cutting a base or band, do you use any lubricant? Your machine finish is impeccable.

 

[srcarr52]

Belt sander seems faster, just sayin’.

When cutting a base or band, do you use any lubricant? Your machine finish is impeccable.

Not usually, I use a high rake carbide insert (CCGX, CPGT, or CCGT -32.51). On some cylinders like the 550/562 I get a little smearing with the alloy which a spritz of wd-40 on the surface eliminates.

I use the same inserts in an 1" carbide boring bar to cut the squish bands. I never have to use any lubricant there and the high rake inserts with the stiff carbide bar peel the nicasil over plating off easy.

 

[Joakim S]

Since there was some questions on mandrels for cutting the base I figured I'd go over how I like to make them.

This is for the 53mm bore (2.085") so I started with a 6" long 2.25" diameter chunk of 6061 T6 aluminum. I cut the end flush and skim cut the surface where it will ride in the 3 jaw for the rest of it's life. I do this so I know I'm clamping on a concentric, flat surface as the raw material surface can be out of round and not exactly flat. I also put a healthy radius on the back edge to keep it from getting caught up in the chuck when clamping and prevents getting a raised edge from misshandling.

View attachment 318243

Then I flip that around and chuck it up, give it a good wiggle as you tighten the jaws so it seats in as true as possible. Then mark jaw #1 so I always put it back in the chuck the same way. Since I have my lathe, jaws and mandrel all marked I'm able to chuck the mandrels back in and bump them out to practically 0 runout across the whole surface.

View attachment 318244

Then I cut to the bore size -0.0005", don't forget to let it cool back down to room temp before your final few cuts. Then I under cut it so you can cut the base or skirt extension all the way to the bore, usually around 0.2" diameter will be enough. I also like to machine the end with a 1/4-20 center tapped hole and a slight recess.

View attachment 318245

That's because I like to put some 80-100 grit sand paper on the end for traction. With the paper I've been able to take 0.02" cuts on the base, but not on a large diameter, interrupted cut like these 585/592 cylinders... I'll stay below 0.015" cuts.

The sand paper also works great to clean up a squish band, remove some debris damage or just check how flat one is by the witness marks.

View attachment 318246

Great Post, Shaun! Very informative. I will do this operation for my first time very soon, so this was just what I needed

 

[Maintenance Chief]

Since there was some questions on mandrels for cutting the base I figured I'd go over how I like to make them.

This is for the 53mm bore (2.085") so I started with a 6" long 2.25" diameter chunk of 6061 T6 aluminum. I cut the end flush and skim cut the surface where it will ride in the 3 jaw for the rest of it's life. I do this so I know I'm clamping on a concentric, flat surface as the raw material surface can be out of round and not exactly flat. I also put a healthy radius on the back edge to keep it from getting caught up in the chuck when clamping and prevents getting a raised edge from misshandling.

View attachment 318243

Then I flip that around and chuck it up, give it a good wiggle as you tighten the jaws so it seats in as true as possible. Then mark jaw #1 so I always put it back in the chuck the same way. Since I have my lathe, jaws and mandrel all marked I'm able to chuck the mandrels back in and bump them out to practically 0 runout across the whole surface.

View attachment 318244

Then I cut to the bore size -0.0005", don't forget to let it cool back down to room temp before your final few cuts. Then I under cut it so you can cut the base or skirt extension all the way to the bore, usually around 0.2" diameter will be enough. I also like to machine the end with a 1/4-20 center tapped hole and a slight recess.

View attachment 318245

That's because I like to put some 80-100 grit sand paper on the end for traction. With the paper I've been able to take 0.02" cuts on the base, but not on a large diameter, interrupted cut like these 585/592 cylinders... I'll stay below 0.015" cuts.

The sand paper also works great to clean up a squish band, remove some debris damage or just check how flat one is by the witness marks.

View attachment 318246

When I see the care you take to get a consistent ,reliable , and repeatable results it makes me question how I get anything to run!
I guess I'm better at being lucky than good.

 

[srcarr52]

The notches on the bottom of the cylinder don’t need any grinding to sit down on the case but you do need to knock the alignment dowels in a bit after dropping the jug.

 

[srcarr52]

Slight problem with taking so much off the base. Now the impulse of the intake isn’t going to seal.

 

[huskyboy]

Slight problem with taking so much off the base. Now the impulse of the intake isn’t going to seal.

Time to break out the welder?

 

[Mastermind]

Slight problem with taking so much off the base. Now the impulse of the intake isn’t going to seal.

How much did you take off?

 

[srcarr52]

Time to break out the welder?

You know it! I'll weld them both later today.

How much did you take off?

I took 0.050" from the squish and 0.053" from the base, they must be on the edge to begin with.