Why some Honda GXH50s lock up during build


Irish John

Some while back I posted a thread about my Honda GXH50 locking up during installation when it ran perfectly before. That thread is on the link below:
I have now discovered what locks the motor up and it's not a piece of black plastic in the crank like I found when I split the engine open down the diagonal. It happens when I remove the governor but it has nothing to do with that either. When I remove the governor I also remove the stock tank and stock exhaust and the stock exhaust black plastic cover is held on by 2 bolts one of which also goes through the Honda start\stop switch and screws into the engine block. This bolt is then used to go back into the start\stop switch to secure it back in place after the exhaust is removed. The bolt screws back in but it goes a little bit further because the exhaust shroud has been removed. When it goes a tiny bit further in it blocks the metal fins on the fan inside the pull starter and this totally locks the engine and stops it turning over. The problem is resoved by putting a small washer and spring washer to stop the bolt before it goes too far and blocks the fan.
I believe that this may only happen on Australian Hondas and that the US ones may use a slightly shorter bolt but it sure took me a while to work out why the motor was locking up every time I used a Honda GXH50. I hope this might help people avoid all the faffing around that I went to the fiirst time it happened. As for the piece of black plastic in the crank that I found last time well it wasn't what locked the motor and I don't know how we fixed it that time.
Here is a picture of the problem and the offending bolt:


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Hondas down under.

Flaming John. Good detective work. I think that most frame mount engines in the US come from Small Engine warehouse. They do not have the tank or muffler cover. They just have the two 4mm bolts that go through the muffler into the head casting which must be replaced with short ones to hold the flange of the exhaust pipe and muffler assembly.

This brings up an other point. These same bolts that held on the muffler also hold a air baffel in place to force the fan air over the fins on the back side of the cylinder. Someone a while ago said he left this plate off when he mounted the new exhaust.

I believe it is necessary to reinstall this plate for proper cooling.

I used the gasket that came wt. the kit as a template and cut out two new flange gaskets. I places one against the head, then the air plate, and other gasket then the exhaust flange. It makes for a thight exhaust asssembly.

There is a untapped hole on the side of my engine that I think would extend into the fan area if it was drilled though and tapped for the exhaust cover.

People using the factory mounted tank GXH50 for a rack mount might run into John's situation.


Thanks Jim, I'm pretty chuffed with my detective work myself. The stainless steel muffler plate from the original stock axhaust isn't required because the air is fanned around the back of the cylinder pretty hard and the wind on the front is gale force at speed anyway. Nobody keeps that plate on cos it looks like a dog's breakfast and it doesn't perform a necessary task except when the motor is running on a bench and driving a pump or something. I actually think it is a heat reflector to reflect heat back from the stock exhaust.
Thanks for the info John.It shouldn't affect me since my engine comes from Staton but u never know....forewarned is forearmed.
This is my 3rd "Fosscati FG4 Billinudgel Bullet" that uses the Schwinn D7 with the springer forks and a Honda engine. Oz Hondas are now cheaper than the US ones because of the terrible value of our dollar in recent weeks. Back in August we were about equal but the cheapest Honda from Small Engine Warehouse with air freight comes to Aus$590.50 now and I'm getting them for Aus$486 from my local dealer and I'm hoping to get a good bit more knocked off now that I'm buying them moderately frequently depending on whether people are prepared to pay the extra above the HS. I get the disqualified drivers asking me for them but I'm a tricky sod and not everyone who wants one gets one.
Anyway my ethos is to try and build a totally local bike with all parts supplied from close by and I reckon the Honda\Grubee is a pretty environmentally sustainable means of transport. It's just a hobby for me and I like trying to make my bikes as reliable as possible. People around these parts are very big on sustainability and environmental footprints and the hardest selling point I'm finding is the noise they make compared to the electric bicycles plus people grouse at the price but I tell them that you can drink meths or you can drink fine Aussie claret but good claret is expensive and even if you drink meths you need to start off with a bottle of good claret! This usually causes them to give me a funny look. I think they reckon I'm a bit mad but when I think how in the last 2 years so many of us in MBc have managed to improve the reliability of our motored bikes we have almost replaced the need to use a car for anything except long distance trips. A well built Grubee 4 stroke outstrips the performance of all those French, British and Italian purpose made bikes of 50 - 70 years ago. Apart from the serious problems with some kit components the next frontier is getting the NV hub onto frame mounted rigs and getting a really decent light to run off the motor.
My HS is still going great now after 5000 kms and I've really had no problems with it but I notice the valve rods are rattling quite a lot more than they used to and although it seems to be the norm with these motors it does sound a bit tinny and detracts from the nice 4-stroke thumper sound. The valve gaps are all set just right but I can't stop the rattle. Anyone else have this problem after a few thousand miles? The Honda does it too but not as badly. Incidentally here is a picture of the offending bolt re the engine locking up as per my above posting.


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Ofending bolt

As I suspected. The bolt doesn't exist on the Small Engine Warehouse engines, nor does the plastic muffler cover. Likewise the kill switch is not included.

You struck a note of sense about a heat reflector, an under speed cooling, but I have lived with 110 F - 120 F summer temperatures for 60 years and have seen the effect on machinery. When the temperature is added to very low humidity levels most of the summer, we are dealing with air that doesn't cool very well.

I remember the UK Spitfires that had the fan 18 behind the rediator. I guess that is OK in the UK, but here we replace 2 row radiators wt. 4 row and add electric fans on the front side to pull desert grades without boiling over.

Sorry to hear about the Ausie dollar decline. Good for exporters, but makes it expensive for us to buy foreign goods. The US has had a cheap dollar for some time.

I just looked at the SEW site and see the price is still US$ 210 for the model we buy. $260 for the model you are getting with the cover, kill switch and gas tank. they are down to around 170 in stock, about 100 less than when I bought mine 4 months ago. I will be interested to see the price when they get a new stock. Japan isn't doing all that well as well, but haven't kept track of the dollar to yen ratio lately.

Is there any in expensive shipping for private parties from the US to the AU?

I buy a lot of stuff for a buddy on Maui in HI. No duities there of course, but we make use of the USPS flat rate boxes the post office has. I am shipping him a battery charger that weighs 8# and will be delivered to him in two to three days. for US$ 9. On line sellers seem to tack on around US$ 20 if you ship to HI?

Anyway it will be interesting long term to see if any of the Hondas developing sticking exhaust valves.

I am a bit cautious as we have a 600 watt Honda generator with valve in block design which is 30 plus years old. Only problem with it was carbon on the exhaust valve stem and the spring keeper fell into the crankcase. Then there is my 11 HP Honda pressure washer. It is overhead valve. I had a stuck exhaust valve and bent a push rod. Both of these engines of course sit for long periods between uses, which may be part of the problem. Anyway it is always the exhaust valve with a problem here in my experience.

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I've never been able to fathom this QXA versus QHA Honda difference apart from the fact that one has a tank and an on\off switch. People have told me the shaft lengths are different but I can't read that on the blurb. I can't believe their shafts vary in length. In Australia they don't have those names for the Hondas GXH 50s but they use other names with Q in them somewhere.
I see they have a 2 year warranty which with the amount of miles I knock up would seem very generous. I think a Honda on a bike would get more cooling than if it was being used for its intended purposes standing stil. On days here where the temperature gets into the 40s centigrade the effect of the wind on my body is greater than the physical strain of pedal assisting on hills so I don't arrive at my destination soaking in sweat.
The Aus dollar has dived big time in relation to the Yen so Hondas will be going up in price. The bigger the financial disaster the better it will be for motored biking in the long term. My superanuation might be up the creek but I'm looking forward to how it all pans out. It's like some sort of "divine chaos" and it is so long overdue it's not funny. When I emigrated to Australia from Ireland I left a low wage economy for a high wage economy but within 10 years that situation had been reversed. It's hard to predict the future but I reckon motored bikes will feature prominently in it.
HA veris XA shafts

In looking at the pictures on the Small Engine Warehouse site it would seem the HA (whuch I know it does) has the step in the shaft that the GruBee clutch stops against. I don't see that step on the XA, but the pictures leave a lot to be desired. I have tried to track the shaft and keyway size but Honda seems to have different standards for various markets?

It would be very helpful if you could post the complete GXH50 esploded view or a link. The US owners manual doesn't include it and you have to buy a shop manual to get a parts list.

I think the HA engines are intended to be intrigued into equipment. The XA is self contained for compressor or pump application. Of note also, the HA does not have the spark arrestor or the screw that retains it. It does come with a fuel pump for tanks lower than the carburetor.

The economic situation knows no bounds and it would seem that no country is exempt. Starting with oil prices. My buddy in Hawaii is paying US$0.48 per kiliwatt for electricity. We pay US$0.05 or 0.15 per KW on a time of day basis. My usage would would have been US$1970.00 for last month. Of course HI doesn't require AC, but a usage of only 184 KW cost US$88.00

The motorized bicycle would seem to be almost the best insurance policy one can have to provide transportation.

Frame mount.

When I bought my QHA from Small Engine Warehouse the shaft was listed as 5/8 x 1 1/4. Now, I see it is listed at 5/8 x 1 5/8 which is the same length as the QXA. I don't know if this is a mistake or a change.