First Build Propane converted EH035 Robin

Discussion in '4-Stroke Engines' started by dnilosek, Dec 4, 2011.

  1. dnilosek

    dnilosek New Member

    A video of my first build. I've been gathering parts and spare change to do it for a couple of years now, but it really only took about 8 or 10 hours to actually get it assembled, and most of the bugs worked out. I only did this because I hadn't seen it done before (I did see a friction drive 25cc propane Robin on You tube but not a chain drive 35cc). I thought I'd be able to get it done, and as it turns out it wasn't too difficult. From an economic point of view, it makes no sense at all. It'd be cheaper to just go out and buy a little motor scooter.

    I welcome any questions or comments!

  2. Silvaire

    Silvaire Member


    I enjoyed watching your build video. Did you ever run your EH035 on pump gas before you converted it to propane?

    I have about 5 of those Lehr engines, and two Subaru EH035's that are still on scooters. I have thought of converting one of my EH035's to propane but I am reluctant to do so. I like the idea of running on propane, but I am concerned about a possible lack of power in making the conversion.

    I found a post on a scooter website stating that the standard EH025 has a 8.5:1 compression ratio (the EH035 is 8.6:1), whereas the Lehr propane engine has around 10.1:1. I haven't measured it myself, and I haven't found any sources that provide hard numbers regarding the Lehr's compression ratio. If Lehr found it necessary to increase the compression to get reasonable power with propane though, I would think they quite plausibly may have made other changes as well, such as ignition timing or cam changes. Even if they didn't change anything else, there is no practical way to increase the compression ratio of an EH035 - short of creating a new taller piston.

    Anyway, I just wondered if you had run your EH035 on auto fuel before converting it to propane, and if so, how the performance compared between the two different fuel types.
    Last edited: Dec 4, 2011
  3. dnilosek

    dnilosek New Member

    I'm afraid I haven't had the eh035 burning gas. Not only that, I have never ridden a motorized bike at all, so I have no frame of reference.
  4. Cavi Mike

    Cavi Mike Member

    I'd love to use one of these engines but they're just so darn bulky. What's under all that plastic and whatever? If you strip them down, are they just as small as the Grubee motors?
  5. dnilosek

    dnilosek New Member

    I looked around the Grubee web site, and the Chinese 4 strokes look like they have a fair amount of plastic and such. Of course those are 49cc while the Robin is 35, but in the pictures mounted on the back of the bike they look to be pretty big. SUbaru Robin has a web site where you can download a spec sheet on the engine, and I'm sure the dimensions are on it. I also saw the dimensions of the CHinese 4 stroke on the Grubee site. CHeck the sites out and see what the differences are.
  6. HeadSmess

    HeadSmess Well-Known Member

    im loving my little lehr 25cc propaneer... as a brushcutter. the oils spotless! though i still change it almost every time i use it.

    wheras its twin,( i bought 2) that i did fit to a pushy...was too underpowered on lpg, not to mention that;

    the carb doesnt like extended wide open periods!!!! ole!

    this meant any more than ten seconds full throttle, then it wouldnt idle. the only way to start it again was to undo the gas line, pull til it coughed, re attach gasline and off i go again! til i next wanted to idle :rolleyes7: im assuming the carb/regulator kept on freezing open, and it was basically "flooding". you could hear the gas hissing out!

    converted to petrol/gasoline. a slight increase in torque and throttle response. and it idles :D

    for some reason this engine turns its oil black instantly! even when it was on lpg...

    get a good range from the 1lb bottles though :) about 100km or so.

    petrol is way easier though.

    and theres still the lil 2speed box i got for it to get finished....too much laziness!

    and regards to what lies under all tha plastic.... not much! the engines (robin, huasheng, whatever) are quite small. the problem is the flywheel! and cooling!

    the flywheel is a fan. its also the widest part of the engine. and without adequate airflow,provided by all that plastic cowling, youll cook the engine.

    if there was some type of small flywheeel available, the average engine would be tiiiiny! so far no-one offers such an option :( other than model aircraft which are expensive...
    Last edited: Dec 12, 2011
  7. Silvaire

    Silvaire Member


    It's interesting that you have the issue of shutting down after 10 seconds of full throttle. This isn't normal. I have one of the Lehr propane powered blowers which has the same engine as the trimmers, and it runs at wide open throttle all the time with never has an issue. I have read somewhere that contaminates can get into the regulator or carb somehow and cause partial blockage. Perhaps this is what is occurring with one of your engines?

    I also have (and regularly use) two of my Craftsman labeled propane weed trimmers. I don't do heavy work with them - just after mowing cleanup - but I love these things. (I did replace the fixed line head with a bump-n-go for a big improvement in useability.) I usually leave them with the propane bottle hooked up after using, and weeks later they will still usually start on the first pull. A couple of times the propane has leaked out though.
  8. I drove a propane powered pickup for a couple of years, and absolutely loved it. I have been told that an engine will last twice as long on propane as it will burning gas. Propane does not contain the contaminates and combustion by products that gasoline does, and burns very clean. I wish my current pickup was propane powered, but the cost of conversion has gone way up after OBDII. My former propane pickup was a carbureted '87 Chevy, and I spent less than $2000 on the whole setup, including a huge bed mounted tank. It mounted where a bed mount tool box would usually mount. It had close to a 1000 mile range.

    I like how you have your chain drive set up without a tensioner or rag joint sprocket. I may have to look into a disc wheel mounted sprocket myself, and it seems the whole thing could be made to be movable to properly tension the chain.
  9. loquin

    loquin Active Member

    The shrouds are used in conjunction with a blower molded into the flywheel for forced air cooling over the fins.

    While you ... might ... be able to get away with removing the shrouds, it may lead to problems later, associated with overheating.

    One of the reasons that the manufacturer uses the forced air cooling, is that it makes the engine temperatures more stable, which allows for improved 'tuning' to help meet epa/carb emissions standards.
  10. HeadSmess

    HeadSmess Well-Known Member

    theres almost no alternative :(

    if you could dispose of the flywheel/fan....

    such as the engines shown here...

    im sure theyll sell the flywheel/cdi as standalone items, but ive never bothered checking into it...

    but when theyre all nude like this you can see how small they really are!

    and how impossible they are to mount!!!! unless one welds "lugs" to the sump, like i planned once... or make a new sump altogether. the way theyre designed you could remove the sump and have it remote mounted with a little effort.

    (starting can be fun when you pull the starter off too! :p)

    im still stewing over plans for a nice engine in the back of my mind...sorting out issues :) one day itlll come together :)
    Last edited: Dec 27, 2011
  11. HeadSmess

    HeadSmess Well-Known Member

    the "freezing carb" issue has been bugging me lately...

    all i can think of to explain it is...

    a brushcutter or blower held at full throttle will rev at full speed! a motorised bicycle struggling up a hill at WOT is still barely above idling speed...

    something the carb/mixer just isnt designed for :( ?

    make sense?

    i never had the issue if i was able to run at a fairly good rpm...

    answers it for me anyway :)
  12. TWalker

    TWalker New Member

    I used to build motored bikes and I stopped a couple years ago but...

    I have 2 Golden Eagle kits just sitting and I had bought the propane conversion kit years ago off Ebay. Yesterday I pulled it all out and started the Honda on propane by just sticking the propane line into the air intake and it ran great!

    But..people keep telling propane runs hot: is this true?

    Any other factors before I hook it up and run it?
  13. Greybeard

    Greybeard Member

    It is not true. I worked with several propane converted engines on the Dyno.
    A gasoline or alchohol fueled engine will have increased exhaust gas temps when they lean out, and if the exhaust gas temps exceed 1400 degrees the engine is not long for this world.

    A propane fueled engine will, like a gas or Alky engine, have low exhaust temps when rich and increase until the A/F ratio is correct, and then (unlike the gas and alky engines) start to fall off again as it goes lean. The end result is that it is nearly impossible for a poor A/F ratio on propane to cause damage. Those racers among us are aware of the distruction of engines that have leaned out under full throttle with other fuels.
  14. dnilosek

    dnilosek New Member

    Check out the for sale section, I'm selling my propane powered Robin eh035 and staton gearbox.