Tuning a smallblock
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LML 187
Joined: 12 May 2020
Posts: 38
Location: England, stoke
Tue May 12, 2020 12:09 pm quote
Hi guys

New to the forum so first of all hello! Been a silent follower of many of the topics, projects/builds for a while.

I have plans for the winter, to add a VMC 177 to my LML motor. To be mated with pipe design exhaust, hopefully for something real fruity!
Currently have the cases split after disaster struck (see pictures) any thoughts? Flywheel was standard weight LML 2.3kg ish which Iím guessing is just too much.

Anyway with the cases split I thought Id match them from my current 166 to the VMC and sort the barrel. Now due to using the longer Conrod and raising the barrel considerably for the port timings, the barrel will sit around 8mm higher than originally intended. This has meant Iíve had to take the spigot openings further back in order to prevent a considerable step into the case ports and also to aid flow.

I think however I might have got a bit trigger happy and Iím worried the bridged areas are now too thin and could crack. (Not sure how stressed this area gets)? I also considered removing the transfer bridges all together but Iím not sure if this could compromise the cylinder and itís fit around the piston

Please can someone tell me Iíve not fooked it cheers

Cheers!
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LML 187
Joined: 12 May 2020
Posts: 38
Location: England, stoke
Tue May 12, 2020 12:12 pm quote
P.s is it possible to post more than one image per message?

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Member
LML 187
Joined: 12 May 2020
Posts: 38
Location: England, stoke
Tue May 12, 2020 12:14 pm quote
Snap[/img]

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Member
LML 187
Joined: 12 May 2020
Posts: 38
Location: England, stoke
Tue May 12, 2020 12:17 pm quote
Porting

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Member
LML 187
Joined: 12 May 2020
Posts: 38
Location: England, stoke
Tue May 12, 2020 12:20 pm quote
Ports

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Member
LML 187
Joined: 12 May 2020
Posts: 38
Location: England, stoke
Tue May 12, 2020 12:25 pm quote
Just to Clarify, current setup is malossi 166, revolver exhaust, 28PHBH MRP reed intake and mazzy bell crank now to be flowed Chiselspeed Tameni 60mm. Probably around 18/19hp so not mega hp at all making the wrecked crank even more of a surprise

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Hooked
P Series / Li / LML / Motobi
Joined: 24 Jun 2019
Posts: 409
Location: UK - 3rd Rock From the Sun
Tue May 12, 2020 12:44 pm quote
in some circles..... mazzuchelli is considered mozzarella
Ossessionato
Joined: 26 Oct 2015
Posts: 2678

Tue May 12, 2020 1:25 pm quote
Crazyfrog187 wrote:
P.s is it possible to post more than one image per message?
Apparently more than one pic per post is possible for some people, but i've never been able to do it with my Apple iphone 6.
Member
LML 187
Joined: 12 May 2020
Posts: 38
Location: England, stoke
Tue May 12, 2020 1:34 pm quote
Gravelrash, yeah Iíd probably say Iím close to being in that camp.

Whodatschrome Iím on 6plus. it would be a lot quicker!
Hooked
58 VB1T, 68 SS180, 81 100 Sport
Joined: 06 May 2019
Posts: 433
Location: Long Beach, CA
Tue May 12, 2020 2:21 pm quote
That busted crank is crazy. And concerning, considering I've got basicly the same one sitting on the shelf waiting to be put to use....
Molto Verboso
2007 Stella 150
Joined: 02 Nov 2019
Posts: 1112
Location: Rochester, Minnesota
Tue May 12, 2020 4:48 pm quote
whodatschrome wrote:
Crazyfrog187 wrote:
P.s is it possible to post more than one image per message?
Apparently more than one pic per post is possible for some people, but i've never been able to do it with my Apple iphone 6.
I have the same issue with my phone, works fine on my tablet.

Last edited by Christopher_55934 on Wed May 13, 2020 2:49 am; edited 1 time in total
Molto Verboso
62 VBB1T Round Tail W/ leaner sidecar
Joined: 26 Jan 2019
Posts: 1777
Location: california
Tue May 12, 2020 7:11 pm quote
Quote:
I think however I might have got a bit trigger happy and Iím worried the bridged areas are now too thin and could crack.
Those bridge areas at the bottom of the cylinder are fairly low stress.
They are surrounded by the cases - so supported on the OD. They are unlikely t implode - so I would say you're likely fine.

Others with more experience can comment if they have ever seen them break under any circumstances. I have not. Beyond thermal load - there is very little actual stress placed on them.

Hope that helps.
-CM
Hooked
58 VB1T, 68 SS180, 81 100 Sport
Joined: 06 May 2019
Posts: 433
Location: Long Beach, CA
Tue May 12, 2020 9:32 pm quote
What would cause the crank to break like that, and in the place? Poor flywheel to crank taper fit? Defect in manufacturing? Both?
Ossessionato
Joined: 26 Oct 2015
Posts: 2678

Tue May 12, 2020 10:43 pm quote
Heavy flywheels, heavy aftermarket reinforced billet clutched, extra horsepower, bad luck, abuse, metallurgical flaws, etc can all cause it. A few snippets of each of those can add up into a snapped crank.

On the SIP website, they have the weights listed for the items at the upper right hand of the screen. I like to try to order the lightest weight clutch as possible, and a flywheel thatís lighter than stock... but not a superlight race flywheel though.
Ossessionato
Joined: 26 Oct 2015
Posts: 2678

Tue May 12, 2020 10:55 pm quote
And hereís a pic of a highly modified stock T5 crank that a local tuner built for me. It was in my reeded T5 172 for a few hundred miles before it chunked out on the clutch side. There was no collateral damage. Itís a paperweight now, but I canít bring myself to throw the crank away. It was so smooth and vibration free at the scooterís top speed, that it almost felt like the jetting was lean (if that makes sense). It was the best crank by far Iíve had in any scooter Iíve owned...well, except for the snapping that is.

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Ossessionato
Joined: 26 Oct 2015
Posts: 2678

Tue May 12, 2020 10:56 pm quote
Another angle...

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Veni, Vidi, Posti
74 Super, 75 Super, PX project, LML off-roader and new to 2018, '66 Blue Badge Smallframe
Joined: 30 Nov 2011
Posts: 7949
Location: Victoria, Australia
Wed May 13, 2020 1:30 am quote
Hi Crazyfrog. As Charlieman says, they are not under much stress. Except if you cut them out altogether, the sides spring in. But not enough to notice. Then you seize. Ask me how I know...

I'm also using a 200 bell crank in a 150 case with spacer. BGM cylinder. It's good so far, really only just got it back together though.

I also had a crank snap like that on my old Polini 218, think it went out in sympathy with the cylinder skirt, but that's another sad story. I never had anything heavier than 1600g on it, but I did use to use a drill and socket sometimes to start it (a different story!) which I think contributed to it's demise. Have a mate with a smallframe who snapped the crank the same way after using a drill - but his was brand new!
The Mazz bell cranks are based on their full-circle cranks, which apparently use a higher grade of steel than their more normal line. My guess is that it was the tiniest bit loose - I usually lap mine on to the taper these days - combined with the heavy flywheel put the extra stress on it.
Jet Eye Master
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 2442
Location: London UK
Wed May 13, 2020 2:16 am quote
Not unique. Your crank snap is the same as Ginch's and the same as mine (pic below). Metallurgist told me it was a regular stress fracture caused by old steel, too many rpm and a taper that didn't fit perfectly.
When they rev to 9000 and up, it seems like there is a limit. Grinding the taper to fit well, light clutch, light flywheel, all balanced and changing crank every few years is going to make it about as good as it gets.

Whats the port timing on your new build? This being the most important detail.

oops_20945.jpg
my 221 a few years ago. looks a lot like yours

Member
LML 187
Joined: 12 May 2020
Posts: 38
Location: England, stoke
Wed May 13, 2020 2:28 am quote
GeekLion wrote:
That busted crank is crazy. And concerning, considering I've got basicly the same one sitting on the shelf waiting to be put to use....
Isnít it!
Member
LML 187
Joined: 12 May 2020
Posts: 38
Location: England, stoke
Wed May 13, 2020 2:50 am quote
Ginch, Charlieman thatís definitely good to hear! Hopefully it holds up.

Jack, quick search after the break. (Roadside I think) I remember seeing yours and another break I think in like you say virtually the same place, not good!

And port timings arenít totally decided upon yet (suggestions would be welcome) but from the info on pipe designs website plus taking into account the rest of the setup. Likely to be 22/68 gearing with the longer LML fourth. I think I will be shooting for around 128/189. I would like to end up with a motor which is strong but isnít too peaky.

The case compression/volume is one area Id like to dig into further. I have likely been running with very low pressure, considering the reed block, spacer for longer crank rod, case port work (rounding corners etc) large ports, long vacuum line for fuel pump and bell crank - soon to be flowed type to add area. Although I still think Adding more Meat to the cases would probably be beneficial (In the dead space where the LML original reeds sat) which should also help to flow the intake better.
From what Iíve gathered the port timings should be higher to compensate for all this, which makes sense however how much higher Iím not so sure.
Molto Verboso
Vespas 1964 GS160, 1965 SS180, 1977 V9A1T, 1983 PX150E
Joined: 16 Apr 2011
Posts: 1519
Location: Siam
Wed May 13, 2020 3:49 am quote
Does this breaking of cranks happen on stock setups as well, or is it something that happens more often with setups using modification kits?
Veni, Vidi, Posti
74 Super, 75 Super, PX project, LML off-roader and new to 2018, '66 Blue Badge Smallframe
Joined: 30 Nov 2011
Posts: 7949
Location: Victoria, Australia
Wed May 13, 2020 5:15 am quote
nomadinsiam wrote:
Does this breaking of cranks happen on stock setups as well, or is it something that happens more often with setups using modification kits?
Think Subetherbass did two like that on stock 150 motors.
Member
LML 187
Joined: 12 May 2020
Posts: 38
Location: England, stoke
Wed May 13, 2020 5:25 am quote
Interesting on the thoughts about why they go. In the process of sorting a lighter flywheel. Either To get mine lightened, or to pick one up new although options seem limited. Iím looking at getting one around 1.9kg if thatís light enough.
Molto Verboso
62 VBB1T Round Tail W/ leaner sidecar
Joined: 26 Jan 2019
Posts: 1777
Location: california
Wed May 13, 2020 8:39 am quote
I suspect "crack propagation" from the corners of the keyway is the culprit.
Metal tends to crack starting at a point.
That point is often from stress at a corner.

You guys probably all know:
When it comes to stress points - corners are bad - radiuses are good.
The keyways have some really sharp corners where the flat at the bottom meets the side wall of the keyway - I don't know why they don't give us larger radiuses in there. That corner then comes right up to the surface of the crank at the end of the keyway.

To make things worse - our woodruff keys have sharp corners poking in to those corners - so they are prying hard right on that high load area. If the key is provided by someone other than the crank manufacturer - then its corners having less radius than the keyway's means it is cutting in to the already prone corner of the crank.


Look at Whodats. His broke cleanly right down the line of the keyway - at the corner where the bottom flat meets the side wall of the keyway.

Jack's and Crazyfrog's broke at the double corner - where the keyway bottom comes up to meet the surface of the crank. Jack's also has corrosion showing that goes down in to the crank below the surface. That suggests that a crack started - and corrosion got in there - from there - its only time.

Recently when I pulled off my flywheel - I was surprised to find corrosion there. If I had to do it again - I would make sure to coat it in grease more carefully before first assembly. I also like to radius the sharp corners fo the woodruff key to avoid having its sharp corners press in to any radius that might exist in the keyway.

My $.02.

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Who dat's cracked right along the line of the keyway. Probably started with small fissure and spread.

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Jacks - like Crazyfrog's cracked right through the corner where the keyway meets the crank surface. Three angles coming together in one corner there. There is a depth of corrosion also that suggests it cracked over time.

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CF's also cracked right through that corner. My guess - it started there and spread. Failure to radius that in manufacture could have left the perfect spot to propagate.

Member
LML 187
Joined: 12 May 2020
Posts: 38
Location: England, stoke
Wed May 13, 2020 11:49 am quote
Charlieman, Interesting reading. Something in it for sure. Like you say the breaks seem to be in more or less the same place. Clearly the slot is the weaker area which makes sense anyway.
Something I havenít mentioned - a few days before the brake I sheared a woodruff key. I also Noticed when putting in a new one it was a real tight fit. This possibly could have had something to do with it also. I think ultimately itís probably a combination of things with the mazzy material quality being one of them in my mind to be honest.
Member
LML 187
Joined: 12 May 2020
Posts: 38
Location: England, stoke
Wed May 13, 2020 12:03 pm quote
New cranks turned up today Lots of scooter goodies turning up, one of the joys of lockdown.

Tameni 60mm 110 crank flowed for reed valve by chiselspeed.

Looks a nice piece of work, atleast itís shiny enough. Hopefully this one lasts better than the last one.

Iím not sure exactly on how a crank would be best flowed for a reed setup, but the fly side web has been rounded considerably and reduced in width in some areas more than others. Itís clear to see the fuel will now flow past much better.

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Member
LML 187
Joined: 12 May 2020
Posts: 38
Location: England, stoke
Wed May 13, 2020 12:04 pm quote
Tameni

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Member
LML 187
Joined: 12 May 2020
Posts: 38
Location: England, stoke
Wed May 13, 2020 12:05 pm quote
Crank

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Ossessionato
Joined: 26 Oct 2015
Posts: 2678

Wed May 13, 2020 12:07 pm quote
We so my T5 crankís defense, it was 25 years old at the time when it broke. Yes, the crank was just rebuilt with a new con rod, but over the years there has been fairly mild stress on it. Then once I tuned the scooter up with a bunch of go fast parts, something had to eventually let loose. Keep in mind that the scooter was my track bike, and therefore saw WAY more abuse than any highly tuned PX street racer would see on the open road. Luckily the crank broke when when the racing season was over. I was at a scooter rally, and after I filled up with fuel I tried starting it (push start only because I had removed the kickstarter gears). The scooter started and went into gear, but it didnít have any forward propulsion. So my advice is to brake parts when your scooterís engine is at an idle.
Member
LML 187
Joined: 12 May 2020
Posts: 38
Location: England, stoke
Wed May 13, 2020 12:35 pm quote
Crazyfrog187 wrote:
New cranks turned up today Lots of scooter goodies turning up, one of the joys of lockdown.

Tameni 60mm 110 crank flowed for reed valve by chiselspeed.

Looks a nice piece of work, atleast itís shiny enough. Hopefully this one lasts better than the last one.

Iím not sure exactly on how a crank would be best flowed for a reed setup, but the fly side web has been rounded considerably and reduced in width in some areas more than others. Itís clear to see the fuel will now flow past much better.
Just to correct this itís the crank side which has had the work, pretty obvious from the pictures
Ossessionato
76 Sprint V, 63 GL, 62 VBB, 05 Stella
Joined: 16 Jun 2011
Posts: 2846
Location: Nashville
Wed May 13, 2020 1:04 pm quote
Going back to your original question on tuning, I'm running an LML motor with BGM with a P200 (110mm conrod) bell crank, PWK34, VForce 4 reeds and a PM Tuning pipe. My timings are 126/176/25. It gets about 21 HP, but peak power is only around 7,000 RPM's. Ton of fun to ride
Member
LML 187
Joined: 12 May 2020
Posts: 38
Location: England, stoke
Wed May 13, 2020 1:58 pm quote
chandlerman wrote:
Going back to your original question on tuning, I'm running an LML motor with BGM with a P200 (110mm conrod) bell crank, PWK34, VForce 4 reeds and a PM Tuning pipe. My timings are 126/176/25. It gets about 21 HP, but peak power is only around 7,000 RPM's. Ton of fun to ride
Thatís good to reference! Blowdown Seems pretty low? Iím guessing it gives you a pretty wide power band and decent low down power too? Iím hoping to get mid to higher 20ís with the PD exhaust and higher port timings
Ossessionato
76 Sprint V, 63 GL, 62 VBB, 05 Stella
Joined: 16 Jun 2011
Posts: 2846
Location: Nashville
Wed May 13, 2020 2:24 pm quote
I have always run it with a box previously, SIP RoadXL before the PM Tuning, and had it producing 25-26 HP on the previous cylinder, but always struggled to keep temps under control. This build is a tamer, but also manages temps a lot better. I miss the broader power band, and more low end power, but am not ready to go back to the box yet. Maybe a Road 3 will show up at my house at some point and change my mind, though...
Jet Eye Master
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 2442
Location: London UK
Wed May 13, 2020 10:11 pm quote
Pipe Design exhausts are my favourite but do need the correct port timing. They will go great with any timing and do the best they can but when the timing is right they really go. 128 could be ok on a 187. 189 certainly is. Aim for 128/190. Make the exhaust port as wide and square as it will go. Keep the squish at no less than 0.9mm, then if the 128 is a bit much you can still drop the packer. 22/68 gearing will be ok on standard tyres but no higher.

Not snapping the new shiny crank will be the challenge. As its new steel you have at least a few years but this will make 10,000 rpm so things will break but a lot of fun to be had before then.
Member
LML 187
Joined: 12 May 2020
Posts: 38
Location: England, stoke
Thu May 14, 2020 12:22 am quote
Thanks Jack, exhaust is most likely either a cobra or possibly the new Daytona which looks to perform better but Iím yet to hear of anybody thatís used one.

From the dyno graphs on the PD page, these exhausts especially the cobra donít seem to rev too far past 8000 even with the higher port timings. PD recommend 130/194 for a strong reed valve motor with the cobra and lesser timings for the Daytona.

I like the curve on the graph with the m1x. 12ps at 5000 pushing up to a peak of high 20ís with a fairly wide power band all without revving too high seems to be ideal. If the graphs can be trusted. If I havent already mentioned before Iíll most likely upgrade to a flat slide polini 30mm carb to hopefully suit.

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Member
LML 187
Joined: 12 May 2020
Posts: 38
Location: England, stoke
Thu May 14, 2020 12:25 am quote
Polini cobra vs bullet exhausts

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Member
LML 187
Joined: 12 May 2020
Posts: 38
Location: England, stoke
Sat May 16, 2020 1:48 am quote
Matched the case to the VMC which has big ports. There isnít much meat at all on the upper side to match to the VMC (as I found out breaking through) JB weld hopefully should do the trick.

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Member
LML 187
Joined: 12 May 2020
Posts: 38
Location: England, stoke
Sat May 16, 2020 2:05 am quote
Iím now considering filling in parts of the crankcase mainly to aid flow and take out some dead space. Firstly in the inlet area of the LML case where the old reed sat. It seems flow would hit the edge/step into the case. The case is thin here and so I canít take much off. But I could fill in the area to flow smoothly from the reed block to the case edge.
Also but more reluctantly Iím considering filling in the area between the transfer spigot bridges and the step into the crank area. Effectively bringing the step further forward so as the flow can sweep over the bridge as it would when the barrel sits lower at the bottom. The spigot bridges as previously mentioned sit so far forward now they are sitting over the start of the port and look as if they would obstruct flow in.
Iím not sure how much of a difference this really makes in reality. I suppose it needs to be worthwhile with the chance of the JB weld ever coming loose. What do you guys think? I think using a longer rod/stroke crank Isnít quite as straightforward as it seems.

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Member
LML 187
Joined: 12 May 2020
Posts: 38
Location: England, stoke
Sat May 16, 2020 2:07 am quote
More

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Member
LML 187
Joined: 12 May 2020
Posts: 38
Location: England, stoke
Sat May 16, 2020 2:09 am quote
Case step

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