Bonsor

[vhgmcbuddy]

Hi

I have just got myself a bonsor truck, the 1 ton model with a 12 hp petrol Kohler 301 pull start engine, 1979 if the serial number of the engine is to be believed. It had not been used for some months after the drive chain between the clutch and the drive shaft broke. It is also missing an exhaust at present. I do not intend to do too much by way of restoration, as I bought it to use, but I want to make sure I get it running well before I start. I am a practical guy but have no experience on engines at all, steam being my main hobby, so please forgive me if some of my questions seem a bit dim!

My buddy and I got it running today for the first time,having cleaned the points and the spark plug.

I have a couple of questions, never having had nor run this sort of thing before. The engine was running for around ten minutes, then when stopped the head seemed to us to be too hot, there is a small amount of accumulated grim on it and this seemed to be “burning” off, the aluminium part of the head is a little corroded too and I was planning to give this a bit of a clean up, but are these engines known for, or designed to run hot? Is the inbuilt fan on the flywheel usually effective?

I checked the oil after the engine had been running, the previous owner having said he had filled it with new oil just prior to my collecting it. The oil was grey though and looked horrendous so we drained it and flushed it through before refilling. Could this have contributed to the hot running?

There is a small lever arm on the underside of the fuel pump that is sprung loaded, is this a priming device?

There is what we believe to be a choke lever on the right hand side of the carburettor. The lever has the word “on” stamped on it and we presume that this is pulled downward away from the cylinder so the “on” is visible to give the run position? Certainly when pushed back it stopped the engine. When it was running it was hard to be sure but it did seem to be running very hard, I was contemplating having a look at the setting of the low and high idle screws n the carb, does that sound sensible?

I think I have a bit of work to do on the clutch too, but I will wait and see about that once the engine is running and I have an exhaust fitted. I picked up a briggs and stratton muffler that I am going to fit, hopefully this should be suitable.

thanks for any replies and I will try to post a couple of pics in the net day or two. The bonsor looks like a great bit of kit and I am looking forward to getting it put to work.

Pete

[charlie]

Pete, welcome to the forum. I am sure one of our regular contributors will be able to answer your questions. As a start I would suggest not altering anything on the carb yet as the engine starts and runs OK. Cleaning out the cooling fins around the head and cylinder would be a good idea too.

[vhgmcbuddy]

Thanks Charlie for the welcome, I will get the head cleaned and see if that makes a difference.

Cheers

Pete

[vhgmcbuddy]

The bonsor was missing the optional extra front bumper. Made a replacement this afternoon. Waiting on filters and need to fit the exhaust that has arrived today.

[vhgmcbuddy]

Got the bonsor moving under power yesterday, gearbox is not great but reverse and first are ok. Now need to sort the brakes as they are somewhat non existent.

Hope the attached video works ok.

Pete

Attachments:

1. Bonsor-1st-run.mp4

[vhgmcbuddy]

So an update, in case it is of use to anyone in the future.

Got new filters from guypartsandservice, ebay, who seems to stock a wide range Kohler parts.

So the first thing to get the engine running was to clean the points, a tiny piece of crude was all that was stopping it, it now start virtually first pull every time with very little effort.

My 13 year old and I stripped the brakes. I was told by the seller that the brakes weren’t brilliant. Actually they were completely seized solid! The actuators were seized, the pads not to bad and everything covered in rust. The brake rods were rusted to death so I made replacements. Got the wheels off, drilled out the countersunk screw holding the drum to the hub and used a gear puller, some heat and lots of wd40 to crack the drum from the hub. Once loosened they came off quite easily. The drums and the hub were wire brushed and painted, the actuator soaked in lubricant and gently teased back into action and once opened up wire brushed and cleaned till free working. The bell crank that works the two rear rods was removed, the guttered holes welded up and drilled to suit the new rods. Then all put back together. The only thing not replaced that I would have liked to was the rubber boots over the connection between the rod and the actuator, I was not sure where to even try for a replacement. Any ideas? Needless to say the brakes now work.

I have re-routed the exhaust, this being a briggs and stratton muffler I had picked up. Initially I had it discharging within the seat box that covers the engine, as I believed it had done originally. However I think this assumption was wrong as the whole cover, fuel tank and engine was getting hotter than I thought sensible. I had a look at some other images online and noticed a few that showed the exhaust attached to the rear chassis between the engine and the rear wheel. That is roughly where it is now sitting. I am still sure a better silencer would reduce the noise of the engine so will be getting a box type one soon.

The clutch and gear box assembly came off friday and the clutch was stripped and clean. The lugs on the plates are very very worn as were the slots in the casing, the whole thing also being covered in thick oily grime. Once cleaned a bit of gentle filing tidied up the lugs, but on re-assembly the nut holding the clutch on the shaft would not go back on. On inspection the thread had stripped out of the nut, but it appeared that the nut had been a different thread from the one on the shaft. The thread turned out to be a rather obscure form so after a bit of work in the lathe with a replacement nut and a suitable pitch tap we were back reassembling! Once together and back in the bonsor the difference was remarkable. Gear change with no crunching! Yesterday I rebuilt all the linkages on the gear lever train as these had over ½ an inch of slop in them, this and a bit of adjustment have actually got the lever sitting where it should when the gears are engaged.

I will take some photos and post them later in the week in case they are use to others int he future.

I have plans to use the truck with a Model Engineering group that I am involved with, who have just started building a new track. It will be interesting to see how it performs. I plan to make a log skid attachment to use in place of the tipping back, as much of the work involves felling and moving timber on the site.

The only major thing I still want to do is look at the adjustment of the carburettor, which I will hopefully get a hand with from a very knowledgeable friend once he is back from a holiday. Hopefully this will reduce the idling speed which I think is a bit high.

Hope this is of some help to folk

regards

Pete

[charlie]

Pete, thanks for the detailed summary of work to date glad to hear of your success it sounds like the Bonser has done a fair bit of work and suffered neglect in the past. Keep up the good work.

[will-haggle]

Try a caravan or trailer shop for the rubber boots, Bonser might have used standard parts….

[Author]

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