Piston design and heat expansion

sam2019

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29. September 2021, 5:06

I got this question via email, a 477 customer asks:
I have measured the piston and it has a smaller diameter at the top when compared to the bottom - is this normal or a defect?
It is the design - pistons are much hotter at the top when in use - and in this region expand more. In particular forged pistons do that which lead to multiple piston failures during our development time because the boring company had not calculated the greater expansion of a forged piston vs. a cast one. This picture may help to illustrate:
The outer line delineates the deformation when hot.
 

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Dool

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Browsing through old picks I found this, it shows the diameter of the piston crown dish and the volume in cc's
Top to bottom, 477Mk1, 450 ( AKA 80mm ) and stock.
Information that is handy when working out the compression ratio of your build, the volume has to be added to the combustion chamber volume.
 

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Sasa

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Browsing through old picks I found this, it shows the diameter of the piston crown dish and the volume in cc's
Top to bottom, 477Mk1, 450 ( AKA 80mm ) and stock.
Information that is handy when working out the compression ratio of your build, the volume has to be added to the combustion chamber volume.
I might be wrong but the first piston seems to be a 500cc! There is an 86mm stamped on top of it...
 

Dool

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Well done @Sasa, did anyone else notice? I didnt :)
The reason I posted the pic was because of reference to the Volume of the Piston Crown Dish, I will check before fitting any of them.
 

Dool

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And Fit one is what I did , with basic Tools and Candle Wax, if I can do it then,,,,,,,,,, ,,,,,,,,,,, :unsure: anyone can?
Should be more 500s around then:giggle:


 

Dool

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Yes, I put down the camera/Phone for the Tricky bits :giggle:
Vacuum cleaner and another pair of hands would be helpful :alien: But even so one pair is enough:unsure:
Beats pulling the Engine out etc etc like about 10 to 1:ROFLMAO:
The Head Bolts and Dowels position the Barrel, what could go wrong:cool:
 
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thony

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Yes, I put down the camera/Phone for the Tricky bits :giggle:
Vacuum cleaner and another pair of hands would be helpful :alien: But even so one pair is enough:unsure:
Beats pulling the Engine out etc etc like about 10 to 1:ROFLMAO:
The Head Bolts and Dowels position the Barrel, what could go wrong:cool:
You are my idol. I know this comes from the old forum but, will it get passed the 500cc at some point down your experiments? Is that even expected haha?
 

Dool

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That's not so bad then, a 4 Valve head would be nice on a 511 with twin 24mm throttle bodies.
Need to source a few of the parts yet :cool:
 

sam2019

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isn't there a 822 in the wild that fits your description?
 

Sasa

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isn't there a 822 in the wild that fits your description?
Yeah, that's an abomination, both philosophically and mechanically...
Well, not sure what to expect from an awarded Hima enthusiast haha

Yes, over 500cc.
I don't know if you want to go much further, the chassis/brake/suspension package is already a little out its comfort zone with a 500cc and all the other mods... The dark chocolate steel out of which the chassis is made wouldn't bear much more than this...

Just so you know, I went the extra mile and asked Harris Performance (the Enfield side company that developed the Hima chassis in the UK) if it would be possible to replicate a Hima frame out of chro-moly steel, making it lighter and stronger, since they already have the project in hand. Unfortunately they declined because they are bounded by an NDA to Enfield and cannot work on a Himalayan outside their partnership with Royal Enfield!
Too bad, as I believe the chassis of the Hima is 8 to 10 kg overweight and the bike could greatly benefit from a stiffer and ligher frame!

Who knows, maybe the new 450 would have an aluminium chassis, highly unlikely since aluminium is expensive and more difficult to weld...
 

thony

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Yeah, that's an abomination, both philosophically and mechanically...

I don't know if you want to go much further, the chassis/brake/suspension package is already a little out its comfort zone with a 500cc and all the other mods... The dark chocolate steel out of which the chassis is made wouldn't bear much more than this...
Sure I get it. It was already quite an experience the other day going over 125... Hima has got a tremendous upgrade with all the work done, the other day I had the chance to help a couple friends climb a very tricky hill and man, there is no point of comparisson. The same when had to ride open road with the Classics and 650s.
 

Sasa

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Sure I get it. It was already quite an experience the other day going over 125... Hima has got a tremendous upgrade with all the work done, the other day I had the chance to help a couple friends climb a very tricky hill and man, there is no point of comparisson. The same when had to ride open road with the Classics and 650s.
Did you sort the issue about the 6000RPM wall??? Does it go beyond 125 now? You should be able to reach the red line easily in any gear!
 

thony

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Did you sort the issue about the 6000RPM wall??? Does it go beyond 125 now? You should be able to reach the red line easily in any gear!
Well, I reached 6100 on the aftermarket tach and got scared of going ahead. I do not have the chance to test red lines on my regular driving days. This time I was open road and flat-very slight downhill so, if 125 is possible 130+ is a matter of manning up :) I was not wearing propper protection and needed to get to work on Monday haha
 

Sasa

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Well, I reached 6100 on the aftermarket tach and got scared of going ahead. I do not have the chance to test red lines on my regular driving days. This time I was open road and flat-very slight downhill so, if 125 is possible 130+ is a matter of manning up :) I was not wearing propper protection and needed to get to work on Monday haha
Well you can redline also in first gear and you’re at about 45km/h, no need for stainless steel balls! 🤣🤣🤣

Anyhow I was just worried bc in the past you mentioned that the bike was reluctant to go over 6000RPMs, I feared there was something wrong with the engine, but apparently it can go there and beyond!
 

thony

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Well you can redline also in first gear and you’re at about 45km/h, no need for stainless steel balls! 🤣🤣🤣

Anyhow I was just worried bc in the past you mentioned that the bike was reluctant to go over 6000RPMs, I feared there was something wrong with the engine, but apparently it can go there and beyond!
@Sasa, seems like I was probably not explaining myself well to my own self when mentioned this the other day. I can rev passed the 6000, I had just not done it in 5th to get to the expected max speed on road, the other day gave it a try under particular conditions but around 125 kmh at 6100 I believe (too many things happening in my mind) I backed off. Felt the chocolate frame kicking in.

In fact, not sure but full throttle in neutral marks 9000 rpm on little aftermarket speedo - the little $12 unit bought only for the break in period -.
 

Sasa

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@Sasa, seems like I was probably not explaining myself well to my own self when mentioned this the other day. I can rev passed the 6000, I had just not done it in 5th to get to the expected max speed on road, the other day gave it a try under particular conditions but around 125 kmh at 6100 I believe (too many things happening in my mind) I backed off. Felt the chocolate frame kicking in.

In fact, not sure but full throttle in neutral marks 9000 rpm on little aftermarket speedo - the little $12 unit bought only for the break in period -.
I see now! I had understood that your bike wouldn’t rev past 6000 for whatever reason!

Anyhow the frame will hold, I went to redline in 5th with 16T sprocket on the highway, and I’m here to tell the story, so it can be done… I wouldn’t go past 145… 🤣🤣🤣
 
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