Archive for February, 2008


Monday, February 25th, 2008

Ok so i painfully re-keyed the other flywheel during the week and reassembled the engine.  It wasn’t until Saturday that i got it all mounted in the boat ready for another try.

Started fine but once again, it would not rev.  I would say that it was marginally better but still only about 60% revs of what it was doing before.  Now, last weekend, Tim’s first thought was that it was the coil.  Something that i didn’t thhink would be the cause (blaming the timing seemed more feasable at the time).  But, as it turns out, i was wrong and Tim was right – We swapped the coil from the original engine and it was perfect!

I’m now even suspecting that this is a deliberate thing – Perhaps MTD/Ryobi deliberately rev limit thier engines to prolong thier life??  Not sure but it would make sense.  The coil is a standard walbro part on the newer ones so i’ll do some research.

I got a new prop – A prather 280.  It’s the biggest they make (AFAIK).  I spent hours sharpening and balancing it so it was bolted on for the trip to the river.

We took the boat down the river Sunday arvo to give it a shot.  It seems that the boat does not like the ‘throw’ launching technique – Every time it seemed to just stall just after it hit the water.  We suspected the prop was just too big so we went back to the 275 but it done almost the same thing but it was  tad better.  In the end we tried a technique of just placing it into the water (much, much harder to do without getting wet…) and it was off!  After some tuning of the high needle we got a reasonable run.  Still more tweaking to do but at least it’s a good starting point.

We never got to putting the 280 back on but that is definately in the next installment.

Check the vid….

So close it’s painful

Monday, February 18th, 2008

Ok, so i spent some time prepping the new engine for the boat – machining the flywheel and the head. I also replaced the fuel tank with an airplane tank to make sure water doesn’t get in again – it’s lighter too so that will help with balance of the boat. I even done a ‘double vent’ on the tank, the vent from the main tank goes to another smaller (2oz) tank to make sure water can not get in.

So, i got it all together ready for a run Sunday arvo but there was something strange happening with the engine. It started and revved lightly but with more than about 1/2 throttle it just sounded as if it was on a rev limiter. It’s hard to explain but it was like it was only firing every 2nd rev of the engine. I messed with the mixture screws a bit but it made no difference.

Some closer inspection has found what i think is the problem. It seems that the ‘key’ that keeps the flywheel in a certain spot in relation to the crank sheared off. I don’t know when it done this but that’s what i suspect the problem was since this is what sets the timing of the engine. It was probably really out.

The simple solution there is to swap flywheels, well one would think anyway… But this revision is keyed to the crank differently. This one has the key cast into the flywheel and is thicker by about 1.5mm. So, to use the other flywheel, i have to make a key and file out the keyway on the original flywheel (while trying to keep it symmetrical so as not to alter the timing). Oh what fun!

More to come…

Happy again

Thursday, February 14th, 2008

Ok, so as per previous post, i found myself pondering how long this motor was going to last.  I figured ‘what the hell, i’ll just run it till it breaks’.  So i popped into the mower shop on my way home from work to grab a head gasket for the motor (I damaged the other one when i pulled it apart).  They were cheap so i grabbed a few.  The sales guy was a bit confused as to why i wanted more than one.  I explained to him that the engine was in a boat etc and that i’m tinkering with it a bit still.

 We got on to the subject of ryobi’s line trimmer division now being owned by MTD, build quality/power when compared to chinese built engines and with that he popped out the back with a ‘just a sec’ and returned with an MTD line trimmer (the 31cc model) and said ‘here you go, it’s yours’.  It was a ‘repair’ that did not go ahead. I wasn’t going to complain – at worst it was probably good for a spare flex cable or something like that.  So i thanked the man and off i went.

Once i got home i just had to check this thing out.  Closer inspection showed the engine wasn’t ceased or otherwise anythng detrimental.  The repair docket still attached to it had ‘Starter broken’ and sure enough it was but that seemed like the ONLY thing wrong with it.

I stripped the trimmer down and it had super compression, much more than my other engine ever had.  This engine (remember still a Ryobi but newer) had 2 piston rings instead of one, no mid support in the exhaust port, longer transfer port timing and these unusual extra ‘mini’ ports on the transfer ports.  The exhaust port is a slightly different shape but that i believe is because of the lack of the mid support (it keeps the ring on the piston).  The extra bits on the transfer ports were weird.  They are like ~1mm gouges up the bore and are about 7-8mm long.  They start from the end of the transfer port.  It’s very odd, i have never seen this in an engine before.

There were also some other minor differences but this engine has done even less work than my original and is better so i’m going to mod this engine to accept the cooling head, machine down the flywheel and shorten the crank so it’s the same as the original engine and give it a shot!

 One problem now is that the tuned pipe will not be so tuned anymore with different port timing and area.  I’ll punch it it to the calc and see what it comes up with…..

Not happy jan!

Wednesday, February 13th, 2008

Ok, well we took the boat out again on the weekend.

Saturday: Bolted on a new prop (Prather 275) for testing.  Took it down the river and managed to get a brief run out of it before the exhaust manifold developed a crack.  While it still ran as such, it was leaning out etc and so we decided to head home.

 Sunday: Repaired exhaust and we decided to have another shot at it.  This time i was much more hopeful that we could give the new prop a good test.  We got it started and went to throw the boat in but Tim slipped a bit (almost going with the boat) and it didn’t hit the water overly nice.  Water went over the bow, tracked the plug and the engine stalled.  We fished it out for a reset.  Started her up and off for another shot at it.  This time it went well.  I managed to give it a squirt down the front straight but then i went to turn and it stallled again.  So, we went to fish it out again but this time we were a little less than successful.  When Tim snagged it with the rod, it was by the rudder so it came in stern first and so did all the water!  The boat was pretty much under water by the time we got it to the bank.  Bugger!  I tipped it up and out came all the water and the fuel!

It seems we had a problem the first time round that we might have got some water in the fuel.  If you look back at a previous post, you will see that i ‘plugged’ a hole in the top of the tank.  It seems the 1/2″ grub screw (which was loctited in) came loose and managed to vibrate down and drop into the tank.  This allowed water in and probably caused the issues.

So, with that, we packed up and headed home again.  I pulled the plug and turned the motor over with the starter to try and clear out all the water.  Lots of oil, turning it upside down etc.  It wasn’t until last night that i looked at it again and oh dear….Seems i didn’t get all the (salt!) water out.  The engine was a mess!  The bearings had started to corrode, the inside of the crank case had started to corrode, surface rust on the rod etc. It was not a pretty sight.

I’ve now cleaned out the engine ready for re-assembly but this is a set back.  In the future, i need to make sure all the water is out if it takes some on but i’m not sure on the best way to do this.  It’s also making me think i need to find an alternative place to be running it.  The salt water just seems to be so harsh on all the components.

The boat hits the water!!!

Wednesday, February 6th, 2008

I am extatic!  First time i put the boat in the water, it sat nice (although slightly bow heavy) and that was a good start.  Tim and i got it started and into the water it went for it’s maiden voyage.  I am ever so happy at how well it ran.  The prop is probably a little undersized but it went really well still.

 The only problem i had was that i forgot the darn video camera!!  So, we used a mobile phone.  No where near as good quaility but the maiden had to be captured.  This also meant unfortunately that the video is sideways :(

Anyway, enjoy!

Almost there!

Sunday, February 3rd, 2008

Well, things have not progressed as well as i’d hoped this weekend for the build.  I had a few issues which caused delays plus other things had to be done over the weekend as well. 

The lid is now on and other things like the radio box were secured in and sealed.  I also made up a bracket to support the rear of the pipe.

Very close now but just not quite enough hours in the weekend to get it watertight and ready for it’s maiden voyage.  A special thanks to Tim for helping me out too!

p2030033.jpg     p2020009.JPG     Lots of foam!!

Boat work continues

Friday, February 1st, 2008

Ok, so now i’ve got the fuel tank all sorted, the Flex drive is all installed and set in epoxy too.


I managed to source a better carb for the unit.  The original was a WT-149 @ only 7.94mm venturi.  So was the WT-682 i borrowed from my other trimmer.  I now have a WT-439 which is a 12.7mm venturi.  This was off of a 34cc MTD chainsaw so it should still be fine for the 31cc.  All the zenoahs and sikks run 12.7mm carbs and they go as low as 20cc. At only $10 i could not really go past it – cheaper than a rebuild kit for the original carb.  It also has a built in choke.  I’m yet to run it with the new bigger carb just yet.  

 I also modified the reed valve in the engine back plate.  I have opened up the relief from about 1.8mm to 3.1mm as reccomened by jagengines and another ryobi conversion site i came accross.  It seems that with the bigger carb, it’s not of much use unless you do this.  Maybe one day i’ll check the difference but for the moment, i’ll take thier word for it.


p1310353sml.JPG     p1310352sml.JPG     p1280351sml.JPG

Still on track for a weekend launch….