Holey Cylinders, Batman!

lcrken · Sep 4, 2010

I've seen several Commando cylinders that have had the fins drilled to lighten them, but never knew how much weight could be saved. I was thinking about using a set of iron 850 cylinders for my short stroke 750 build, and decided to find out if drilling was worthwhile. I drilled the fins from the top in the mill, and it took several hours.

I was thinking about turning it over and also drilling some of the fins from the bottom, as well as milling out some weight on the side, but wanted to see if it was worth the additional effort first. I measured the cylinders before and after, on a freight scale that weighs in half pound increments. I figured that was accurate enough. I weighed some alloy cylinders while I was at it, for comparison. The results were enlightening.

Iron 850 cylinder - 21 lbs.
Iron 850 cylinder after drilling - 20.5 lbs.
Maney alloy 850 cylinder - 11.5 lbs.
Old DRE alloy 850 cylinder - 11 lbs.

If I'd done the rest of the drilling and milling, I don't think I would have saved more than another half pound. I think I'll be using the Maney cylinder for the 750!

Ken

highdesert · Sep 4, 2010

Ken, some dumb questions from me.

You saved a half of one pound. How does this benefit you? Do the cylinders now disperse heat faster, I assume you are racing at high revs?

You had an overheating problem before?

swooshdave · Sep 4, 2010

1. I think hobot just had a stiffy.
2. You need a better scale.

Hobot · Sep 4, 2010

Dang Ken, I'll hang that one up in my shop so I don't mess myself in home.
I have weighted each drill hole in stuff like battery tray. Who knows with your crude scale except its more art work than mass relief. 80 holes per 8 oz = ~1/10 oz each. A pound would need 80 more of same mass removed. 1/2 lb off = ~1/8th hp relief. If 750Peel hadn't warped by rev's I'd be begging to buy that holey artifact.
Can't use it on a factory plain jane either.

swooshdave · Sep 4, 2010

I bet if you stuck that on the mill and took off every other fin CCM-style you'd save a lot more weight.

davamb · Sep 4, 2010

For what it's worth - little bit of math:
surface area lost = 2 * pi * d^2, surface area gained = t * pi * d
where d is the diameter of the hole and t is the thickness of the fin.
For an improvement in passive convection cooling, the area gained shall be greater than the area lost:
t * pi * d > 2 * pi * d^2
or
t > 2d
or
d < t / 2
i.e. you will increase the overall surface area available for cooling as long as the diameter of the hole is less than half the thickness of the fin.

mikegray660 · Sep 5, 2010

I'm thinking maybe a salad and some situps might have a better effect on "weight reduction" and overall health of the rider :shock:

Rich_j · Sep 5, 2010

lcrken said:
I've seen several Commando cylinders that have had the fins drilled to lighten them, but never knew how much weight could be saved. I was thinking about using a set of iron 850 cylinders for my short stroke 750 build, and decided to find out if drilling was worthwhile. I drilled the fins from the top in the mill, and it took several hours.

I was thinking about turning it over and also drilling some of the fins from the bottom, as well as milling out some weight on the side, but wanted to see if it was worth the additional effort first. I measured the cylinders before and after, on a freight scale that weighs in half pound increments. I figured that was accurate enough. I weighed some alloy cylinders while I was at it, for comparison. The results were enlightening.

Iron 850 cylinder - 21 lbs.
Iron 850 cylinder after drilling - 20.5 lbs.
Maney alloy 850 cylinder - 11.5 lbs.
Old DRE alloy 850 cylinder - 11 lbs.

If I'd done the rest of the drilling and milling, I don't think I would have saved more than another half pound. I think I'll be using the Maney cylinder for the 750!

Ken

You could have calculated that without wrecking a usable barrel :roll:

MexicoMike · Sep 5, 2010

At the age of many of us here, the best way to lose weight on the bike is to lose some weight...

Hortons Norton · Sep 5, 2010

Very true, Mike.

britbike220 · Sep 5, 2010

I am sure hobot is holed up in his shed with a lap top looking at those pictures in private. I don't see a lot of sense in ruining parts by driiling holes in them except maybe a disc for a brake for street use or unless it is for racing, but I'd have to concur with several other answers about personal weight being lost as a big gain.

lcrken · Sep 5, 2010

davamb said:
For what it's worth - little bit of math:
surface area lost = 2 * pi * d^2, surface area gained = t * pi * d
where d is the diameter of the hole and t is the thickness of the fin.
For an improvement in passive convection cooling, the area gained shall be greater than the area lost:
t * pi * d > 2 * pi * d^2
or
t > 2d
or
d < t / 2
i.e. you will increase the overall surface area available for cooling as long as the diameter of the hole is less than half the thickness of the fin.

I take your point, even though you got the lost surface area calculation wrong. The surface area lost is actually twice (top and bottom of fin) the area of the hole, which is pi times the radius squared, not the diameter squared. It turns out that you are gaining total suraface area when the diameter of the hole is less than twice the thickness of the fin. I did the calculation before I decided to use 1/4" drill bit. It's not exactly right, but close enough for me.

Actually, I wasn't trying for more surface area. I was just curious about how much weight was saved.

Ken

lcrken · Sep 5, 2010

highdesert said:
Ken, some dumb questions from me.

You saved a half of one pound. How does this benefit you? Do the cylinders now disperse heat faster, I assume you are racing at high revs?

You had an overheating problem before?

I didn't mention cooling or overheating. It's not about that. As I said in the post, I was interested in whether the weight saving from drilling fins was significant. This was an experiment to quantify the weight saving. I concluded that it wasn't worth the effort. On a race bike, you look for all the weight saving you can find, but there is a limit where the effort exceeds the benefit, and for me, fin drilling is past that limit.

Ken

lcrken · Sep 5, 2010

swooshdave said:
1. I think hobot just had a stiffy.
2. You need a better scale.

Probably, or at least the part about the better scale. Stll, 1/2 lb. increments were enough for what I wanted to know. I do have a couple more accurate scales that I use for balancing and such, but the larger one is still limited to 10 lbs. max.

Ken

lcrken · Sep 5, 2010

MexicoMike said:
At the age of many of us here, the best way to lose weight on the bike is to lose some weight...

A point I agree with completely, Mike. Unfortunately, I have other folks ride my race bikes now that I'm old and feeble. I've noticed that no matter how much weight I lose, they don't go any faster.

Ken

lcrken · Sep 5, 2010

Rich_j said:
You could have calculated that without wrecking a usable barrel :roll:

Who said it was usable? This isn't the cylinder I was planning to use for the engine, it's a junk one I used to experiment. If it was a good one, I'd have been more careful about the hole placement. I plan to eventually cut it up some more in some lifter mods I want to try out. Waste not, want not.

Ken

swooshdave · Sep 5, 2010

lcrken said:
MexicoMike said:

At the age of many of us here, the best way to lose weight on the bike is to lose some weight...

Click to expand...

A point I agree with completely, Mike. Unfortunately, I have other folks ride my race bikes now that I'm old and feeble. I've noticed that no matter how much weight I lose, they don't go any faster.

Ken

In that case, crack another cold one! :mrgreen:

C-Bat · Sep 5, 2010

Lighten the load Bro...

http://i928.photobucket.com/albums/ad12 ... 1283741095

The simple truth is that, notwithstanding the drilling out of the primary case, front hub and the Akront aluminum wheels, the ultimate variable is the rider and his weight. The bruuuuskies don't help and have offset whatever weight advantage that I have gained!

grandpaul · Sep 7, 2010

lcrken said:
I do have a couple more accurate scales that I use for balancing and such, but the larger one is still limited to 10 lbs. max.

Actually, that would be the BEST scale to use.

Once you come up with a cylinder that doesn't peg the needle on THAT scale, you have reached Nirvana.

cash · Sep 7, 2010

I bet if you stuck that on the mill and took off every other fin CCM-style you'd save a lot more weight.

We used to slit the fins on a band saw and just break them off with a pliers. It was done to keep the fins from blocking with mud and it worked a treat.

Cash

Holey Cylinders, Batman!

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