Free Lawnmower

No progress on the topic of the last thread yet, will try and get some time on that over the long weekend if the Renault timing belt change doesn't throw up any problems,

Dad's friend gave him this ride on lawnmower for free...

Looked pretty good, needs a bit of welding to the mountings of the pedestal the steering wheel goes through and a bit of a re-rig on the various linkages to get it sweet

Started stripping it down, wiring was all sound, needs to be routed and secured better

The engine would only rotate about an 1/8th turn each way, I was hoping that this was just some part of the drive system underneath catching so everything was disconnected from the output shaft of the engine, with everything disconnected the problem remained so next step is head off. Simple job on a side valver.

Cylinder head bolts

With the head off it was found that the piston moved independently of the crank, hohnoh

Needs to be opened up.

Head off and getting the engine on the bench

Engine up on the bench, the tail of the 'oil' pouring out of the filler shows how viscous this oil was, it was tar really

I didnt think about getting the flywheel off first so temporarily bolted it back to the chassis and removed it with an improvised puller

Flywheel off

Time to open the crank case

It was a mess inside

Camshaft gear well out of mesh with the crank, counterweight broken free from the crank

Chunk of 'big end' with fastener still attached so the bolts didnt let go!

Broken counterweight, its retaining rod disconnected

Smashed up counterweight assembly

Broken pieces, notice how oil free the rod journal on the crank is!

One galled up journal surface, this was the cause of the failure, no oil and it seized

When the bearing locked up it broke the rod, then imbalance and broken bits jamming the works caused failure of the counterweight 

Amazingly the crank case survived

Looks like the piston has been replaced before, showing less wear and colour than other parts

Cleaned up a bit

All the cooling fins on the cylinder and all the ducts on the flywheel fan rotor where packed with grass, I think that with age and overheating the oil has gone to shit and formed the horrible tar that was left. Oil starvation to the crank piston journal then caused failure of the big end bearing causing the rod to go.

The case, camshaft, piston and governor assembly seem to be salvageable, but everything else is shagged.

Parts list sees a crank, con-rod / gudgeon pin and counterweight assembly added to ze list.

More on this and the mower as they get sorted.

YeeHaaah

PCB Holder

Right,

One of the many jobs in the works is the construction of an awesome electronics kit which will unlock more stuff, more on that in subsequent posts.

To assist the build of this kit and subsequent other electronic projects a decent holder will make flipping between sides of the board for soldering a lot easier. Im sure these things are available commercially, but one can be made pretty easily.

Finest quality engineering polyethylene

Base marked up

Rough cut out with a jig saw

Loaded onto the mill for milling to size

The polyethylene mills easily

Milling corners, this was the biggest shape that I could get out of the chopping board, this is derived from the size of the PCB that this is going to work with first

Blocking up uprights from the thicker board as these will need to hold threads later

Marked for drilling

Drilling

Cutting the counterbore with an endmill, depth marked with tape as the Z axis handwheel markings are pretty useless, the kit that will made at the end of this will remove this problem completely...

Drilling the uprights

Tapping uprights M5x0.8

Clip and spindle assembly made from plated coat hanger wire and crocodile clips, bonded with epoxy then heat shrink finished 

More heat shrink makes soft jaws

Uprights fixed with socket head cap screws

PCB holder done, the clips can be moved in and out to accommodate different size boards, the screws on top of the uprights lock the spindles so the board can be held in any orientation

Thats that,

The PCB shown in the last image is the basis of the kit that will be covered in following posts.

Job's good,

Pete

Yamaha Tri Z Decompressor Valve

First post.

Primarily the write ups that will appear in this blog serve to post notes and images on the net that will hopefully provide assistance in some form or another to people searching for random things like these, or just for something to read for the technically interested. Secondly if I end up feeling compelled to update this page then I have at least created a source of inspiration to continue working on things for the desire of getting more life in my years... more so than can be gathered by drinking tea watching National Geographic and Discovery Turbo.

On to the subject.

A couple of years ago we bought an offroad buggy from my parents neighbour, who deals in plant and field toys. It originally started out as a Yamaha Tri-Z trike, but since then has been completely rebuilt with a tubular chassis, the front end of the commercially available quad conversion kit and a dual swing arm chain drive assembly.

Tri Z Buggy, far removed from the original trike

With the engine now fitted in the back the kick start has been removed and replaced with an electric starter from a motorbike. To keep the overall bulk and weight down the starter system employs a decompressor valve to allow a smaller motor and battery to crank the engine over.  The decompressor valve takes the form  of a poppet valve that runs in a sleeve screwed into a threaded boss that is welded into the cylinder head. The valve is held closed by an external leaf spring that engages in a groove at the end of the valve shaft, and a single 'e' clip is used to retain the valve in the sleeve.

Last week my brother limped the buggy the back to the garage following a blast round the field complaining of a loud hissing noise from the engine and it having little power, it was immediately obvious that the valve was missing from the sleeve. It had lost its e clip and vibrated out of its notch in the leaf spring and fallen into the engine.  Sweet.

Decompressor boss 7 o'clock from centre spark plug hole, decompressor sleve already removed,
leaf spring visible lower left

The head had to come off, fortunately on this port valved 2 stroke it is simply a case of the 6 head nuts.

Head off, some impact marks visible on the piston crown (sad face), but no valve?

Valve found smashed into the head. Hoohray.

Valve removed from head with the aid of a cold chisel and a sacrificial piece of ali to protect the surface

Decompressor Assembly, sleeve on top, knackered valve below

The valve was completely un-serviceable, and is not an off the shelf part. A cup of tea later and work started, im still in the process of saving up for a lathe, which would of made this a nice little job. Instead improvisation was required and the trusty mill and a drill chuck were called up.

Bit of mild steel rod cut to working length

Rod chucked in mill

Valve taking shape

Gloves only worn to avoid leaving moisture on the mill, makes cleaning down and avoiding surface rust easier

Valve cut down to near finished dimensions, next to lap the valve to the valve seat

For this application this technique was deemed permissible!

Valve seat nice and even

Valve cut to final length

New valve and seat assembly

Decompressor valve assembly trial fit in the head to determine valve lift permissible without fouling the piston

Underside of above image, all sharp edges and bulged deformities were filed down, for this engine this should be sufficient to avoid hot spots

Without an accurate way to groove the shaft for a retaining clip I opted to mig on a couple of nuts to provide retaining for the lift and close actions, this valve should never fail in this fashion again.

Completed decompressor valve assembly

Valve assembly re-installed in the cylinder head

Head going back on, head nuts were torqued down to 18ft/lbs in standard alternating fashion

All disturbed parts were then reinstalled and the coolant refilled and bled etc.

The valve works great, starts well and seals perfectly,

Job's good.

More random items to follow,


Taa

Pete