1906 Rover

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A tale of two lawnmowers

Monday, March 1st, 2010

This is an account of how I acquired and improved two Bolens lawn tractors

H11 XL Bolens lawn tractor

In 1980 we started to look for a ride-on lawnmower.  It was obvious that a lawn tractor would be best suited to our needs and we eventually found an 18 month old 11hp HXL demonstrator model.  It was far more sturdily built than any other mower we had seen of this size.  Over the years, however, several weaknesses have become apparent, most of which I have dealt with using scrap parts I had lying around on my farm.

11hp engine

The 11hp Briggs and Stratton engine was very under-powered for the hydrostatic version of the mower that we had, and consequently tended to overheat.  Removing part of the sides of the bonnet did help, but the engine still required attention every year.  After a few years I looked round for a new replacement short engine and found a 14 hp HXL lawnmower that had been scrapped.  The engine, a 14hp Tecumseh, ran but the hydrostatic pack had gone wrong and several of its parts had gone missing.  I bought this mower, intending to make one good mower out of the two and to keep any usable spare parts in case they might be needed at some time. The Tecumseh engine was stripped down, checked and reassembled, then the complete transmission out of the 11hp mower was fitted into the 14hp mower.  The result was a machine that ran for 10 years without needing further attention other than routine maintenance.

Having constructed one useable mower from the two I then turned my attention to the remaining parts.  I found that the hydrostatic unit from the 14hp had suffered at the hands of someone who did not understand how it worked, but that I could repair it.  To do this I made new bushes for the oil charge pump from steel backed engine gudgeon pin bushes, a squash plate from a thick, steel cultivator leg.  I also turned oversize hydroclamp pistons from silver steel and hardened them.  Having repaired the hydrostatic unit I just needed a good engine to have a second working mower, so I wrote to Briggs and Stratton about not being able to get parts for a seemingly standard 11hp engine and about the overheating problems that the 11hp engine had suffered from new.  They took the engine back to look at it, and informed me that this particular type of engine was not used in large numbers.  It was called a cross-over engine, and was designed to produce a high torque for a small engine by having an extra long inlet manifold.  It was not ideal for this overloaded application.  I was told that parts were not available but that they had a complete engine that had been used on test and that they would update this to electronic ignition for me, as a good will gesture.  A few weeks later I received back a rebuilt engine.  I now had a good second working machine, which we use for trailer work, and as a backup lawnmower.  I have never known an engine to run as rough on idle as this model, this annoyed me so, with some misgivings, I decided to alter the cam shaft.  This resulted in a significant improvement, but is by no means perfect. I was reasonably satisfied as the mower is only used occasionally

H14XL Bolens lawn tractor

Eventually the Tecumseh engine started to use oil and developed a nasty rattle.  The cost of reconditioning it was going to be rather high, so I looked around for a new replacement.  I decided on a 16hp OHV Vanguard V-twin Briggs and Stratton.  This fitted in fairly easily, with very little modification to the chassis being necessary.  Some extras were needed; an oil filter adapter, a fuel pump, a silencer, and a dual shaft kit.  I am extremely pleased with the result, since I now have a mower that is quiet, extremely smooth running and economical.  I think I would have to go a long way to find a better machine.  I use my improved mower to mow about twice as much grass as I did before, because of the effortless cutting.  The only problem I encountered during this modification was that when the engine was started for the first time it would not switch off.  On looking at the wiring diagram I saw that the ignition was shorted to earth through the starter solenoid coil to stop the engine.  My new engine has two ignition units and I found that it could not be stopped by shorting them out in this way, however fitting a relay unit and putting it direct to earth worked.  I do not know why this should be so, perhaps an electrician can explain it.

V-twin engine, right hand side

V-twin engine, lftt hand side

Weaknesses I have discovered over the years and the modifications I have made:-

  • On the front axle the trunion bush welds break loose.  I have replaced this with a better engineered part and made it greasable.
  • The king pin bushes break up.  This is easily improved.
  • The drive to the charge pump on the Danfoss hydrostatic pack suffers from severe wear on the splined drive hub.  This is a common fault, one which I have often seen poorly repaired.  The soft hub is, in fact, easily repaired.  It is twice the length of the input shaft’s spline on the pump, cutting off the three-fingered spider then accurately welding it on the opposite end will make it as good as new.  However, if it is not done correctly the out of balance spider will very quickly result in the pump bushes knocking loose, which is very difficult to put right, requiring a modified casing.  Normally the splines on the pump wear very little. If the hub is refitted using Loctite high strength 638 it should not come loose again, however stopping this movement means a modified drive shaft is required to allow some sliding movement.  I found a very light duty agricultural power take-off shaft (called a lemon shaft because of its shape) was suitable.  I made this modification 12 years ago and it has not shown any signs of wear or of the hub coming loose. (I have mounted my V twin engine rigidly; because of the smooth running this completely eliminates the movement allowed by the old rubber mountings that caused or aggravated the problem.  It also eliminates any mis-alignment resulting from the rubber mounts sagging, previously the engine needed re-aligning occasionally to prevent premature failure of the flexible drive discs.)
  • The side-discharge cutting decks crack in various places.  These were welded and steel pipe struts were added, they haven’t cracked again.  Following these repairs they were grit-blasted and hot-dipped galvanized.
  • On the cutting deck the rollers, shaft and bushes wear quickly.  Fitting ball bearings to the shaft support brackets, pushing steel tubes right through the rubber rollers and then threading one end of a new shaft to make it into a long bolt which goes right through, makes a completely solid unit.  The rollers now turn as a whole unit. An unexpected benefit is that the short end rollers will self-clean when cutting wet grass.
  • I have found that Mountfield blades will fit with a little modification.  They last much longer and cost less.
  • The center alloy bearing housings can break.  I made a light steel housing from two pieces of pipe.
  • Having both an 11hp and a 14hp tractor I have found that each has its advantages.  The 14hp obviously has more power but it had a hydraulic lift on the cutting deck, where the 11hp has a hand-operated mechanical lift.  I found the mechanical lift gave me more control. On rough ground the cutting deck sometimes needs slight support or needs to be lifted over an obstruction, the hydraulic lift was too slow and too vague to do this, I had to guess how much support I was giving to the deck.  I removed the hydraulics and made a copy of the hand control unit.  All I had to make was the quadrant, the handle came from a scrap New Holland combine.
  • I found that the idler pulleys could be replaced, when necessary, with pulleys from a scrap combine harvester.
  • Some parts of the electric clutch can be replaced with parts from a car or commercial air conditioning pump clutch.

2 Responses to “A tale of two lawnmowers”

  1. Raleigh Sajorda says:

    This is a terrific blog, I’m lucky I stumbled onto it. I’ll be back in the future to check out other posts that you have on your blog.

  2. Rik says:

    Great write up.

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