Author Topic: 30cc Flat Four (Puma)  (Read 9243 times)

Offline doubletop

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Re: 30cc Flat Four (Puma)
« Reply #45 on: July 09, 2019, 08:59:49 PM »
Interesting comment Brian, must admit I was in the camp that thought a very wee clearance was required before using loctite.  Do you have the loctite number for press fits, I will get some in!   :ThumbsUp:

Nice piston rods Pete.

Chris

Thanks Chris

Pete
?To achieve anything in this game, you must be prepared to dabble on the boundary of disaster.? - Stirling Moss

Offline doubletop

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Re: 30cc Flat Four (Puma)
« Reply #46 on: July 15, 2019, 10:22:19 AM »
Well I rolled the dice and, as I had a busy week ahead, decided not to start anything major. So did things like gudgeon pins, cam follower bushes etc. Then the bearings arrived so I was able to do the crank bearing holders.

That allowed a trial fit of the everything Iíve done so far.



This also allowed me to try out the timing belt sprockets. But that led to a bit of a disaster.



Drilling the crank sprocket to fit the 5mm stub on the end of the crank it fell apart (compare to the good one on the left)

Checking the supplierís catalogue and anything up to 16 teeth is a type 1 on the right are type 2 and they start at 18 teeth. So, it has to be a minimum of 18 teeth on the crank and 36 on the camshafts.

A bit of an update in the CAD and it looks feasible. The order will be placed tonight.



Youíll notice Iíve also included an alternative, simpler, exhaust pipe, the ľĒ x 32 spark plugs and a carb sourced from Hobby King.


Pete
?To achieve anything in this game, you must be prepared to dabble on the boundary of disaster.? - Stirling Moss

Offline doubletop

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Re: 30cc Flat Four (Puma)
« Reply #47 on: July 15, 2019, 10:43:59 AM »

A brief video of the trial fit. No pistons yet so it turns quite freely and the conrods can be heard rattling in the bores


Pete
?To achieve anything in this game, you must be prepared to dabble on the boundary of disaster.? - Stirling Moss

Offline doubletop

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Re: 30cc Flat Four (Puma)
« Reply #48 on: July 22, 2019, 03:41:50 AM »
I could do with some help please. These timing belts arenít going to work.  After the 12x24 combination fell apart after drilling the smaller pulley to fit the crank I ordered a set of 16x32 and 18x36 pulleys. Belting Online got them to me in 3 days UK-NZ.

The 16x32 pulleys fit with 160mm belt and the next belt size of 177.5mm has too much slack to be taken up with an idler in the space available. The larger pulley of the 18x36 set were too large.



The other problem will be assembly. With the cams on the camshaft it will be impossible to get the 32 tooth pulleys and belt located on the cam shaft with the 16 tooth pulley already on the crank.

So its back to looking at gears. Iíve drawn it up using metric Mod 1 gears. It all seems to go together OK but with a  bit of underlap on the PCD dimensions. Gears are 12, 24 with a 15 tooth idler.

(PCDís are the dotted lines and O/Dís are the full lines.



I have little experience of gear selection so any thoughts please?

Pete
« Last Edit: July 22, 2019, 04:30:19 AM by doubletop »
?To achieve anything in this game, you must be prepared to dabble on the boundary of disaster.? - Stirling Moss

Offline bruedney

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Re: 30cc Flat Four (Puma)
« Reply #49 on: July 22, 2019, 06:15:34 AM »
Pete

Is the reason you can't do the belt because you can't side the belt on once all the pulleys are in place?

If so then do like they do in full scale and only have a lip on the rear of the pulley

Regards
Bruce
ĎResults! Why man, I have gotten a lot of results. I know several thousand things that wonít work.í ó Thomas Alva Edison

Offline Jasonb

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Re: 30cc Flat Four (Puma)
« Reply #50 on: July 22, 2019, 07:06:20 AM »
Can't you just make your own 12T pulley from solid, or rather than pressing the toothed part onto a boss as the bought ones? Or have those two solder or loctite on the flanges for easier tooth cutting.

That's if you really need flanges on the small one with the larger pulleys being so close I doubt you do as the belt won't wander far. Which would make the 16T viable and also easier if you make your own 12T
« Last Edit: July 22, 2019, 07:14:19 AM by Jasonb »

Offline doubletop

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Re: 30cc Flat Four (Puma)
« Reply #51 on: July 22, 2019, 07:59:15 AM »
Thanks for the input guys.

Yes Bruce that's the problem

I had thought about removing the flange and I really don't need to remake anything. I could just Loctite the existing 12T straight onto the crank stub, even with a small flange the bearing, which has a 10mm ID, will go over it as pulley as that is a tad under 9mm dia.

Unless I get more input overnight that says I need the flanges I'll see how it looks in the morning and report back.

Pete






« Last Edit: July 22, 2019, 08:23:38 AM by doubletop »
?To achieve anything in this game, you must be prepared to dabble on the boundary of disaster.? - Stirling Moss

Offline doubletop

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Re: 30cc Flat Four (Puma)
« Reply #52 on: July 22, 2019, 10:07:35 AM »
Why wait until the morning?

This looks like it s going to be feasible as long as the belt stays on the 12 tooth pulley without flanges. What is more it looks a whole lot better than those oversize camshaft pulleys.




The 145mm belt has just enough slack to allow easy installation and also allow a tensioner to be included. There may even be scope for a 10mm flange on each end and be able to get the bearing off if neccessary.

You will notice that the existing flange is still there. After drilling and reaming there was enough meat left to hold it on. However, it has to go as it is 13mm diameter so if the pulley is held on with Loctite the bearings could not be removed.

Pete




?To achieve anything in this game, you must be prepared to dabble on the boundary of disaster.? - Stirling Moss

Offline stevehuckss396

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Re: 30cc Flat Four (Puma)
« Reply #53 on: July 22, 2019, 10:59:58 AM »
If it were me I would try to leave the flange on the crank pulley and remove the flanges on the 2 cam pulleys. You really only need the flange on one of the pulleys and it probably doesn't matter which one has it. My thought is to keep the flange on the pulley driving the belt. Unless the cam pulleys are misaligned (highly unlikely) the belt should track around the cams without any trouble.
Do not be like the cat who wanted a fish but was afraid to get his paws wet.

Offline doubletop

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Re: 30cc Flat Four (Puma)
« Reply #54 on: July 22, 2019, 11:40:56 AM »
If it were me I would try to leave the flange on the crank pulley and remove the flanges on the 2 cam pulleys. You really only need the flange on one of the pulleys and it probably doesn't matter which one has it. My thought is to keep the flange on the pulley driving the belt. Unless the cam pulleys are misaligned (highly unlikely) the belt should track around the cams without any trouble.

Steve

The problem I have is because of the small dimension of the crank pulley (9mm) the boss came off when I drilled and reamed it to fit the tail on the crank. Take a look at the earlier photos

Pete
?To achieve anything in this game, you must be prepared to dabble on the boundary of disaster.? - Stirling Moss

Offline stevehuckss396

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Re: 30cc Flat Four (Puma)
« Reply #55 on: July 22, 2019, 11:30:39 PM »
Duh! yep I see it now.  Well you ask for any thoughts on gears. My thought is to put two idler gears either inboard or outboard of the cam and crank gear instead of one in the center. Get the centers spot on so there is minimal slop in the gear train. Make them as small as possible so they wont stick out too far. With a little luck you might even get them on the inboard side of the gears as long as they dont touch in the middle.

 
Do not be like the cat who wanted a fish but was afraid to get his paws wet.

Offline Johnmcc69

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Re: 30cc Flat Four (Puma)
« Reply #56 on: July 23, 2019, 12:33:48 AM »
 :ThumbsUp:
Nice solution Steve! Would look great too.

 Builds looking great Pete, hope you get everything worked out.

 John

Offline Brian Rupnow

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Re: 30cc Flat Four (Puma)
« Reply #57 on: July 23, 2019, 01:05:44 AM »
It'll be a noisy little rascal with a total gear drive solution. If you want to stay with a timing belt drive, can you cross-pin thru the small timing pulley and thru the end of the crankshaft. If you can, it doesn't matter that the hub came off.

Offline Jasonb

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Re: 30cc Flat Four (Puma)
« Reply #58 on: July 23, 2019, 07:07:01 AM »
Offset Idler, no wthat sounds familiar. Oh yes, that's what I went for on my flat twin version, suppose as they are lightly loaded a plastic idler gear could be used if you think noise will be an issue, hopefully the exhaust should drown out most of the mechanical noise.


Offline doubletop

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Re: 30cc Flat Four (Puma)
« Reply #59 on: July 23, 2019, 11:10:42 AM »
The offset idler was Malcolm Stride's original design. Rather than have two I considered a single would do the job. What I wasn't sure about was the relationship between the gears. Do you design for absolute PCD alignment or is it a case of best fit? Malcolm used a piece of paper to allow the setting the gap between the gears. Jason's photo also has a piece of paper in place.

Having been given the suggestion that one of the flanges can be dispensed with Iím returning to the original use of synchronous belts. More by luck than design the 12x24 pulleys and the 145mm belt seem to fit well and allow the inclusion of a tensioner. The CAD package indicated that a 145mm belt would be too tight. So a synchronous belt is the way Iím going to go for now and Iím now onto making the four cylinder heads.

An example of the benefit of being able to validate thoughts on these forums. It generates a whole lot of good ideas and saves a whole lot of time and cost resulting from any incorrect decisions being made.

Thanks.

Pete
?To achieve anything in this game, you must be prepared to dabble on the boundary of disaster.? - Stirling Moss