Basket Cases

[Greg Harding]

Hi Everyone,

Tony, John said oven at 600 degrees C for 3 to 4 minutes, I assume so it brings the heat up evenly and quickly to release the aluminum casting off the sleeve. Yes it is too hot as cast aluminum melts at 570 degrees C if my memory serves me correctly, but 3 to 4 minutes would not be long enough to reach melting point.

John, thank you for your excellent post and suggestions, high quality photos, lateral thinking and problem solving all rolled into One! I do like minimalist shrink wrapped clutch covers as they reduce weight and engine size. You have changed my opinion on narrow twin down tubes with your beautiful photos of Sprites.

After much consideration and head scratching (hair is getting thinner), here are my thoughts: As for using the 44M cases, it is not really an option for me as they are 25 mm wider than 247 and that would make the motor almost as wide as an M. A. R!

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Plus getting it apart was a nightmare as the crank had grown inside the cases, after cutting the con rod, I adapted my hydraulic puller and used heat to separate. This worked for a bit, so I added levers to separate the cases and actually broke the front engine mount in the process! Interestingly the gearbox looks perfect by comparison.

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Having a big gap between 1st and 2nd is counter productive as I like a gear for every occasion, low final drive ratios actually moves the gear ratios closer together.

OK, so back to the 242 cylinder option, welding the 8 mm stud holes is problematic as they are deep and to "V" them out to get penetration for welding would distort the cases, only to drill and tap half of the hole on every occasion I think is asking for trouble.

330s are beautiful bikes and certainly look the part, I hope to ride one some Time? The 51M 348 motor would be an interesting option but I don't have One!

My original thoughts were to use bits that I have and improve on the bikes of the day using period parts.Imagine 247 reliability with 242 handling, 247 bike, Check, 242 rolling frame, Check, 44M crinkly finned cylinder, Check, Cappra wheels, Check, assortment of other parts, Check

So I think I am back to crinkly finned cylinder with 247 liner on 247 bottom end, armed with suggestions from the Brains trust and thinking about it way too much I have decided on bead blasting the 44M cylinder and getting a mate to weld up the ports to make it as George suggested permanent. If for some reason access is limited, my instructions will be to build a dam wall of weld, allowing enough material to match port. Machine top and bottom, bore to suit 247 liner, heat and insert liner and then use liquid metal to change shape of ports and ride off into the Sunset! Dreamer!

As you have probably guessed, I don't fully understand how the ports work and therefore what would be an improvement, but I am wide open to suggestions about 247 porting as now would be the time to make adjustments for bottom end to midrange Power?

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[David Lahey]

Here is a link to a facebook page that has a posting with lots of photos of a hybrid twinshock that reminded me of what Greg Harding is doing. It is a TLR200 motor in a Cota 200
https://www.facebook.com/groups/hardtof ... ooledmono/

The post is called "hondesa raffle"

This link takes you to one of the photos

https://scontent-syd2-1.xx.fbcdn.net/v/ ... e=597D16CE

[JC1]

That Hontesa looks very nicely done.

Hi Everyone,

Tony, John said oven at 600 degrees C for 3 to 4 minutes, I assume so it brings the heat up evenly and quickly to release the aluminum casting off the sleeve. Yes it is too hot as cast aluminum melts at 570 degrees C if my memory serves me correctly, but 3 to 4 minutes would not be long enough to reach melting point.

Yes that's my understanding of it too. It goes on to say, when reinserting the sleeve, "using a suitable press, maintain approx 75lb (35kg) pressure on the sleeve until the entire assembly cools"

600C (1100F) does sound a bit hi tho. For comparison, the Clymer manual for Bultacos says, "Heat the furnace to 700-800 F (370-426C). The old liner will drop out when cylinder temp reaches approx 700F (370C). Do not exceed 800F (426C) because the aluminium alloy cylinder may be damaged"

You'd actually think a lower temp would be sufficient for refitting the liner (compared to removing it) cos the liner is cold & not subject to expansion to the degree it is in removal.


Re: porting. Greg it looks to me from the dimensions you've given, that you could line up the top of the 247 transfers (on the OD of the liner) with the top of the transfer ducts in the 44M cylinder by milling about 4mm off the top of that cylinder. But of course you won't know for sure till you bore out the cyl to take the 247 liner & take accurate measurements of the heights of the ports & ducts. If that cyl is 7mm taller than the 247 cyl that'll leave about 3mm to come off the bottom.

Hopefully if you match the top of the transfers, the top of the boost port should be close to matching as well, but that will depend on the angle of the top of the boost port(s)/duct(s). You may have to correct some mismatching of the height there.

Assuming that woks out, the bottom of the 247 liner's exhaust port should be very close to matching the base of the exhaust duct in the 44M cyl - a happy coincidence! (Taking 4mm off the top of a cyl with 64mm stroke should bring the base of the ex & tranfer ports down to 60mm - the same stroke as the 247).

If the exhaust duct is wider than that of the ports in the liner you could safely benefit from widening the liner's ports to match. At any revs that will promote faster evacuation of the cyl allowing for better filling with air-fuel mixture & hence better power.

However the top of the ex duct will be somewhat higher than the top of the ex ports in the liner. It will still run, as Dave testifies on his Sherpa, but with no alloy behind that part of the liner where it's subject to the hi temps of combustion, heat dissipation will be compromised in that area so it could be prone to distortion & perhaps nipping up. If your mate can weld in the top of the ex duct & taper it back to the exit that would be worthwhile. But that may well be problematic as soot/oil may be impregnated in the alloy by now.


Regarding the width of the transfers, I'd think you could safely benefit from widening the liner's transfer ports to match that of the ducts in the cylinder. You have to be a bit careful to keep the velocity up in the ports at lower rpm for good scavenging & volumetric efficiency & hence good low-mid range power, but I wouldn't think it'd be a problem widening those transfers a small-ish amount like that, as it seems to me these engines are a bit strangled in that area anyway. As a byproduct that should improve top end a little too.


But regarding that cavernous inlet tract, which is also set low in the cyl like it is: it's going to need considerable re-alignment/filling. Going by the dimensions that you've previously posted, the top of the 44M inlet port is 6 mm lower than the 247s so if you take 4mm off the top of the 44M cyl (as discussed above) you will also need to take 2mm out of the top of the inlet duct to match the 247 liner, which should be no problem to do, but it further increases the cross-sectional area of the inlet tract.

The bottom of the 44M inlet is a massive 9mm lower than the 247's so when you take the 4mm off the top of the cyl you still have 5mm you need to fill in the bottom of the cylinder's inlet duct to match the 247's liner.

And you still have a problem with the widths - both the inner width, where it bifurcates around the boost port, and the outer width. Once you have filled-in the boost port duct in the cyl to match the narrower one in the liner (as discussed in previous posts) you will have to remove about 5mm from each of the inner walls of the inlet duct and fill about about 5mm on each of the outer walls. Then give some thought to tapering the whole inlet duct back to a 26/28mm carb instead of 34/36mm.

As you suggested, you could get your welder to 'build a dam wall of weld' at the interface with the liner, then backfill with JBweld, but still ... that's a hell of a lot of work!

Much simpler/easier just to use the 247 cylinder, but I understand why you want to do it.

[TriCub]

Hi Everyone,

You'd actually think a lower temp would be sufficient for refitting the liner cos the liner is cold & not subject to expansion to the degree it is in removal.


(have to go; more soon)

John if you do the sums on thermal expansion the liner will have "0" clearance when the barrel is at 200 C and the liner cold but to get it in and line up the ports before the clearance is lost I take them to around the 350 C mark. Even at 350 you only have a few seconds to get it in and line up the ports. Once it starts to cool it is into the press with 10 to 15 ton on it until cold.
Getting the sleeves out is never as easy as the shop manual describes and if they drop out at 200 C then it would have only had .0005" interference instead of the .004" in should have.

[RL250]

A couple of photo's of my RL250 I have been working on, special thanks to Greg Harding for supplying me with the fuel tank and carby.

[outforfun]

The RL250 looks like she just rolled out of the factory. You should be proud of all your hard work. The blood, sweat and tears too.

[RL250]

Thanks outforfun it was a great fun project, on the hunt for my next one.

[Guy53]

Can you fly to Canada and come fix my TY ?

Guy

[JC1]

That's a very nice RL. Compliments to the restorer.

John if you do the sums on thermal expansion the liner will have "0" clearance when the barrel is at 200 C and the liner cold but to get it in and line up the ports before the clearance is lost I take them to around the 350 C mark. Even at 350 you only have a few seconds to get it in and line up the ports. Once it starts to cool it is into the press with 10 to 15 ton on it until cold.
Getting the sleeves out is never as easy as the shop manual describes and if they drop out at 200 C then it would have only had .0005" interference instead of the .004" in should have.

Thanks for those calculations George. The temperature you use is very close to what the Clymer Bultaco manual recommends. Sure rules out using JBweld etc before re-inserting the liner.

[RL250]

Thanks Guy
Would Love to come to Canada maybe we could do one of them resto shows HaHa
Cheers Steve