Author Topic: 30cc Flat Four (Puma)  (Read 25370 times)

Offline doubletop

  • Full Member
  • ****
  • Posts: 362
  • Wellington NZ
Re: 30cc Flat Four (Puma)
« Reply #165 on: September 22, 2019, 10:12:56 AM »
Another video of a run today.

<a href="https://www.youtube.com/watch?v=_SRKxsPd9BQ" target="_blank">http://www.youtube.com/watch?v=_SRKxsPd9BQ</a>

At around 1 min 50secs a shot of the tacho, it shows just over 8000rpm. Lots of smoke from the exhaust which affects the smooth running. I know it is oil as it got all over the camera. So, it is time to think about the oil baffles.
 
Then at the very end a sudden stop and everything is locked up. An “Oh Bu88er!” moment and the thoughts of what I might find when I looked inside and lots of re-work

First thing was one of the rockers had moved on its bush



Quickly fixed with a cleanup and Loctite

Draining the oil and taking the sump off there was a bit of gunk generated from the running.



Nothing major to be seen inside, and it now turned over freely. Then a tiny pin dropped out, it took a moment to think where it came from. Then realised it was one of the crank retaining pins.



Again, easily fixed with a good clean out, primed with Loctite primer and secured with high strength Loctite.

I then time for the oil baffles for the sump. I decided to give my version a go.



If that doesn’t work then I’ll try something like this.



Pete

« Last Edit: September 22, 2019, 10:30:51 AM by doubletop »
?To achieve anything in this game, you must be prepared to dabble on the boundary of disaster.? - Stirling Moss

Offline DavidLloyd

  • Jr. member
  • **
  • Posts: 2
Re: 30cc Flat Four (Puma)
« Reply #166 on: September 22, 2019, 10:35:51 PM »
Congratulations on that engine Pete.

A good build log,

DavidLloyd,

Offline doubletop

  • Full Member
  • ****
  • Posts: 362
  • Wellington NZ
Re: 30cc Flat Four (Puma)
« Reply #167 on: September 23, 2019, 04:23:06 AM »
Art, Dave

Thanks for your feedback.

I've not had time to try another run today, had other chores to deal with. The weather isn't looking too good for the next 2 days o i could be later in the week.

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

Offline Johnmcc69

  • Full Member
  • ****
  • Posts: 792
  • Erie Pa., USA
Re: 30cc Flat Four (Puma)
« Reply #168 on: September 24, 2019, 01:22:37 AM »
 :ThumbsUp:
 Excellent work Pete! A beautiful runner!
Real nice design work on that.

 John

Offline doubletop

  • Full Member
  • ****
  • Posts: 362
  • Wellington NZ
Re: 30cc Flat Four (Puma)
« Reply #169 on: September 24, 2019, 08:00:07 AM »
Thanks John

There is still work to be done to make it more reliable. I now know that with the sudden stop the timing went out and when I tried to start it today it wouldn’t.

At first, I thought the worst and the wayward pin had jammed the camshaft and moved one of the cams. It turns out that I was correct about the camshaft jamming but what had shifted was the timing belt had jumped a tooth or two. I had been advised that it may be a problem as I didn’t have enough ‘wrap’ on the crankshaft sprocket

So now I’ve had another look and where in the past I had thought I could not use the next stock size belt (160mm) I now think I can fit it in. I’ve spent the afternoon on it and am having trouble getting the rear bearing mount out. So I’ve just shut up shop and come in for my dinner. When I go back out again, I will be in the frame of mind for a complete strip down rather that mess something up by trying to take a short cut.

More later in the week.

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

Online Jasonb

  • Full Member
  • *****
  • Posts: 9466
  • Surrey, UK
Re: 30cc Flat Four (Puma)
« Reply #170 on: September 24, 2019, 09:30:21 AM »
It seemed to run OK with the shorter belt in normal running.

I'd personally prefer a belt to jump in a jam up than something get bent or broken

Online Vixen

  • Full Member
  • *****
  • Posts: 3075
  • Hampshire UK
Re: 30cc Flat Four (Puma)
« Reply #171 on: September 24, 2019, 09:45:14 AM »

When I go back out again, I will be in the frame of mind for a complete strip down rather that mess something up by trying to take a short cut.

Pete

Hello Pete,

If you decide to do a complete strip down, would you be good enough to do a critical examination of the O ring piston rings and report back. It looks like they can handle the compression and power strokes but do little in the way of oil control and what about wear?

Your feedback would be very useful to others considering following the O ring route.

Playing with and developing small I/C engines is great fun and very gratifying. I have been quietly following along from the start.

Cheers

Mike

#OringvCI
« Last Edit: September 26, 2019, 11:05:58 PM by Vixen »
It is the journey that matters, not the destination

Sometimes, it can be a long and winding road

Offline doubletop

  • Full Member
  • ****
  • Posts: 362
  • Wellington NZ
Re: 30cc Flat Four (Puma)
« Reply #172 on: September 24, 2019, 09:49:54 AM »
It seemed to run OK with the shorter belt in normal running.

I'd personally prefer a belt to jump in a jam up than something get bent or broken

Jason

I found it easy to get it to slip, maybe the belt has stretched a bit with running. I’ve stopped for now to reflect on my options. I’ll take another look in the morning and see if I just need to work on the belt tension of go for the 160mm belt

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

Offline doubletop

  • Full Member
  • ****
  • Posts: 362
  • Wellington NZ
Re: 30cc Flat Four (Puma)
« Reply #173 on: September 24, 2019, 09:58:28 AM »

Hello Pete,

If you decide to do a complete strip down, would you be good enough to do a critical examination of the O ring piston rings and report back. It looks like they can handle the compression and power strokes but do little in the way of oil control and what about wear?

Your feedback would be very useful to others considering following the O ring route.

Playing with and developing small I/C engines is great fun and very gratifying. I have been quietly following along from the start.

Cheers

Mike

Mike

I plan to remove the cylinders so will take the pistons out and get some photos. I purchased a second set of O rings so now it has run in a bit I may take the opportunity to replace them.

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

Offline doubletop

  • Full Member
  • ****
  • Posts: 362
  • Wellington NZ
Re: 30cc Flat Four (Puma)
« Reply #174 on: September 25, 2019, 11:09:23 AM »
Getting it all apart after it had been sealed up with gasket gunk was a mission. It took a bit of ingenuity and some cobbled together tooling to release things without making to much of a mess. There’s not a lot to see apart from a pile off oily bits so no photos.

However, I did promise photos of the pistons.





I had expected more vertical marking on the pistons but there isn’t anything major. The O rings look fine so I’m going to leave them as they are.

I’m going to go for the 160mm belt with more ‘wrap’ on the crank pulley. I’ve made the mods to the tensioner. In the meantime, the crankcase is back in the paint shop as it came off worse in the disassembly.

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

Online Vixen

  • Full Member
  • *****
  • Posts: 3075
  • Hampshire UK
Re: 30cc Flat Four (Puma)
« Reply #175 on: September 25, 2019, 02:20:27 PM »
Hello Pete,

Thanks for the feedback about the O  ring piston rings. They certainly look to be an acceptable alternative to the normal iron compression rings, and a whole lot easier. It's not clear if they are so effective as oil control rings

Mike

#OringvCI
« Last Edit: September 26, 2019, 11:06:21 PM by Vixen »
It is the journey that matters, not the destination

Sometimes, it can be a long and winding road

Offline doubletop

  • Full Member
  • ****
  • Posts: 362
  • Wellington NZ
Re: 30cc Flat Four (Puma)
« Reply #176 on: September 25, 2019, 10:31:39 PM »
Hello Pete,

Thanks for the feedback about the O  ring piston rings. They certainly look to be an acceptable alternative to the normal iron compression rings, and a whole lot easier. It's not clear if they are so effective as oil control rings

Mike

Mike

I agree but I really don't have the experience to comment. Both my Lynx and Bobcat chuck out oil and they have CI rings. But with the Puma being a flat 4 it will tend to burn oil more than an upright engine so a direct comparison would be wrong. Jason has a similar experience with his Ocelot.

I used O rings because I saw that Brian used them succesfully. However, he uses a single larger O ring and it occurred to me last night that  hybrid may work O ring on the top CI ring at the bottom.

What it really needs is an experienced builder to do a comparison, 2xCI rings, Single large cross section O ring, 2 x O rings of same dimensions as the CI rings, 1x CI 1x O ring.

Then again its down to personal experience and preference. O rings have worked for me this time as this engine worked just about first go, but thats probably more to the approach I took to getting it to run. With the other two I was very green and had no idea which of the many variables I needed to address, so spent a lot of time tinkering with one thing after another hoping that it was the one. Although they ran they were never perfect, and the engines went on the shelf to look pretty. Once the Puma has got to its shelf time I plan to dust the others off and give them another go.

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

Online Vixen

  • Full Member
  • *****
  • Posts: 3075
  • Hampshire UK
Re: 30cc Flat Four (Puma)
« Reply #177 on: September 26, 2019, 12:14:14 AM »
Pete,

An oil control ring and it's groove is a completely different animal to a compression ring. To be effective, the oil control ring needs sharp vertical edges to scrape the excess oil film off the cylinder walls; the extra oil is returned via radial holes drilled though the piston skirt at the bottom of the oil control ring groove. Larger width oil control rings, can also have radial slits to double the number of edges available to scrape off the excess oil.

Oil control rings are usually fitted below the compression rings and occasionally in the piston skirt below the wrist pin.

Most of our model engines only have one or two compression rings and very few are designed to include a true oil control ring. Your Puma build shows that two O rings look to

#OringvCI
« Last Edit: September 26, 2019, 11:09:11 PM by Vixen »
It is the journey that matters, not the destination

Sometimes, it can be a long and winding road

Offline Brian Rupnow

  • Full Member
  • *****
  • Posts: 7575
  • Barrie, Ontario Canada
Re: 30cc Flat Four (Puma)
« Reply #178 on: September 26, 2019, 01:29:54 AM »
Viton o-rings do an incredible job of sealing a piston in a cylinder. Based on experience, I use a single 1/16" nominal cross section o-ring in a 0.094" wide slot x 0.058" deep in the piston. Would they serve as an oil control ring?--I think they would. The oil in the crankcase only gets thrown into the cylinders on one side. I built my twin cylinder opposed engine without a wet sump, because of experience that Jason had with oil control in a very similar engine. My engine has a lift off cover, held in place by magnets, that allow you to lift the cover and oil the con-rod big ends and small ends with an oil can. This avoids any oil control problems.  If I had the time and patience, I would remake the pistons on the "oily" side, and have one Viton ring at the top end, and one Viton ring close to the bottom end, with a series of 1 mm holes thru the piston skirt immediately below that Viton o-ring.  I've never done that, but I think it would work well for oil control. The only downside to using Viton rings is that they have a considerably higher drag coefficient in the cylinder than cast iron rings. This doesn't really matter in a throttled engine, but greatly affects the number of "coast" cycles that the engine will do before it hits again. They won't work in a two cycle engine that has ports in the cylinder wall either, as they will "bulge" into the ports and either stall the engine dead or be quickly eaten away by repeated passes over the port.

Online Jasonb

  • Full Member
  • *****
  • Posts: 9466
  • Surrey, UK
Re: 30cc Flat Four (Puma)
« Reply #179 on: September 26, 2019, 07:19:07 AM »
Biggest problem for most of us would be scaling down a proper oil control ring and suitable skirt thickness. With pistons of 20-25mm dia the skirt is usually around 1mm thick by the time you add on groove depth you will have a wall of maybe 2.5mm and then start to get problems with the conrod hitting the piston not helped by the fact most models have pistons that tend to be equal or longer than the diameter not short ones with cut away sides. Then there is the fun of drilling a 1mm x 1mm cross section iron ring and fitting it without damage! Also with many people adding a small amount of oil to their fuel you will get some of that coming out the exhaust.

Vitron Quad-rings would likely have more of a scraping action, I do have a casting kit that specifies one of these as the only ring and from what I have seen of them running they work well Though a bit of oil out the exhaust may not be a bad thing as we don't have enclosed rockers, guides, and oil in the top of the engine in a lot of cases.

I've only run o ring sin the slower IC engines with a single or below iron rings. Current Midget engine project will be higher revving and only O ring sealed so we shall see how that goes.

 

SimplePortal 2.3.5 © 2008-2012, SimplePortal