OutdoorKing Repair Forum Forums Restoring, Customising and Modifying Tech Talk Kirby H4-4A engine rebuild

I own a mid-70s Scott Bonnar cylinder mower (Type 45) fitted with a Kirby H4-4A engine. When I got the mower the engine wasn't running, and hadn't run for some years, but would turn over. The previous owner did say that it was a bit smoky when it did run. The rest of the mower wasn't in bad nick, so I decided to undertake a restoration, including an engine rebuild.

The first issues I encountered were identifying the engine and then sourcing parts. To cut a long story short I discovered that the engine was based on a Lauson (US) model. Lauson were a manufacturer of small engines who were bought out by Tecumseh (US) who then licensed Kirby (Aus) for local manufacture and parts distribution in Australia. Kirby has long since folded but parts are still available in the US.

Basically these engines are quite robust and well built but had a reputation for being a bit finicky and, when running, a bit agricultural. Over the years, most owners with mowers fitted with these engines replaced them with either Briggs & Stratton engines or more modern Japanese equivalents (eg: Honda G100). Being something of a masochist, I decided to try to resuscitate this motor.

This is what I found -

Kirby 4H-4A = Lauson (Tecumseh) H30(A)
Bore 2 5/16" (58.74mm) x stroke 1 13/16" (46.46mm) giving a displacement of 7.61cin (125cc).
Horsepower 3.00
4 cycle L-head (side valve) vertical, single cylinder.
Air cooled
Cylinder is die cast aluminium alloy with a shrunk in steel liner
Piston is heat treated aluminium
Con rod is aluminium alloy
Piston rings are 1 x compression, 1 x scraper and 1 x oil control ring
Crankshaft is heat treated cast iron
Top bearing alloy, lower bearing ball race.
Cylinder head is aluminium alloy
Magneto ignition

So far, fairly standard.

After lots of research, I ordered parts from MFG Supply (http://www.mfgsupply.com/) in Wisconsin, US and Outdoor Distributors (http://outdoordistributors.com/index.html) in Alabama US. Both were very helpful, priced well and delivered overseas at reasonable cost. Locally available parts were the oil seals, roller bearing and new muffler.

I've attached a couple of photos of the parts.



Oil seals, bearing, carby gaskets, crankcase gasket and rings.



Coil and plug lead, valves, points, needle valve and main jet and head gaskets.

I will continue the story with more photos soon,
Chris

I've attached photos of the complete mower after hosing off all of the cobwebs and dust and a closeup of the engine. Motor mower manufacturers seem to have this mania for painting everything on the engine - carby, springs, levers, engine itself and cowling.

After cleaning I removed the throttle cable, unbolted the engine and slipped it off the mower base. The cowling comes off easily though the fuel feed passes through it. When doing this, take note of the throttle assembly - how and where the throttle cable attaches, where the return and governor springs are attached and the positions of the two rev limiting screws.

The carby assembly comes off easily and once removed, I sprayed it liberally with carby cleaner and put it aside. Once again I took care not to disturb the mixture and idle screws.

The head is held on with 8 bolts - 3 long and 5 short. Two of the long screws have loose collars.

The remaining photos are of the partially stripped engine.



The beast after hosing off.



The Kirby engine - I'm surprised that they don't paint the spark plug as well ....



Rear of the engine (output shaft side). The oil seal has to be drilled for removal. The output shaft is a standard keyed 5/8" diameter stepping up to 3/4" at the seal.



Front of engine with cowling and starter gear removed. The keyed flywheel can be removed safely with an appropriate puller. Timing assembly and points are underneath.



Inlet/exhaust side with valve cover/breather removed. The lever is linked to the internal governor.



Interestingly, there was nothing on the engine to identify the model - only a riveted aluminium plaque fixed by Kirby

More soon,
Chris

This next bit is on the bottom end stuff.

After drilling a couple of small holes in the oil seal and then picking it out, the small circlip beneath can be removed. This then frees the rear half of the crankcase for removal.

The governor is an interesting device. It is a shaft mounted device close to and gear driven from the crankshaft. When the little weights deploy as engine speed increases, they push on a disc then on an internal lever that is attached through the crankcase to the spring loaded external lever and thence to the throttle butterfly via a bent rod. Clever and a little more sophisticated than the air-driven Briggs & Stratton governors. The connection passing through the crankcase is suitably sealed against oil leakage.

The internals are quite standard with crank, camshaft and valve lifters in the usual places.

More photos are attached - taken after cleaning 30 years of crap out of the crankcase.



Bottom bearing, crankshaft and circlip prior to installing new oil seal.



Governor with top disc removed showing the weights deployed.



Reassembled governor.



Valve lifters and governor lever. I've still got a bit more paint to remove off the air vanes.



Bottom end showing oil splasher. Apparently, some of the US models had a small oil pump and pressure lubricated bottom end.



New bearing in outer half of crankcase. Now so clean you could drink your soup out of it

I have to go out now, but I'll pick this up later,
Chris

Cylinder and head stuff.

Having stripped the engine completely, I had a good look at all the parts.

The bore was fine and I did a very light hone. Similarly, the piston, con rod and both bearing surfaces were OK.

The rings looked OK but given the smoky history, I replaced them just in case making sure that the gaps were staggered away from the valves.

The head was in good nick but very coked up so it got soaked in cleaner and tidied up.

The valves also looked OK and after cleaning the faces I did a light paste grind with them in situ by using a spring compressor. I checked the tolerances on reassembly. A new head gasket and all was done.

Engine torque settings are as follows -

Head bolts 22.5Nm
Con rod bearing cap 11.5Nm
Flywheel nut 54Nm

Valve clearance is 0.10mm to 0.20mm

A few pictures -



Lining up the marks for the static timing.



Smooth bore, ground and reset valves.



Slightly scuffed piston with new rings. I'm sure it'll be OK.



Piston ready for reinstallation.



Head bolt tightening sequence.

Timing is next,
Chris

Timing, I'm told, is everything. For the art of repartee it's 'better never than late'. For engines it's 'early is good'. So how early?

Anyone who has set the static timing on an old-style automobile engine will know that it is set a few degrees before top dead centre (BTDC), that is, it is advanced, and there is usually a mark on the flywheel to help. Line up the timing mark and rotate the distributor until the points just start to open - easy-peasy. Unfortunately, all single pot mower engines don't have distributors because they don't need one and also you usually have to remove the flywheel to access the points, so putting a mark on it won't help. Therefore, the timing has to be set using another method.

Some engines have a preset advance built into the mount for the points (eg: Briggs & Stratton) but on the Kirby engines the advance must be set and to do so, the head must also be removed from the block.

Start by fitting new points and setting the gap - at this stage it doesn't have to exact, just close - and don't connect them to the magneto. Wire up a battery (small torch battery will do perfectly) and an appropriate voltage light. Connect to the points so you can monitor when the points are open (no light) or closed (light illuminated). I just use my multimeter set to the ohms range and monitor the displayed resistance.

For the rest of this, you'll need a dial indicator and an appropriate mount.

Rotate the engine clockwise (looking at the magneto end of the crankshaft) until you find TDC. Here the piston will be at the top of its travel and both valves will be closed. Set up the dial indicator so that it is touching the piston crown and check that at TDC, the gauge on the indicator reverses direction as the piston starts to descend in the bore again. Next rotate the crankshaft counterclockwise until the piston has descended about 3mm BTDC. Now slowly rotate the crankshaft clockwise again until the dial indicator shows the piston at 1.65mm BTDC. For the H30 engine, this is the piston position on the compression stroke where the points should open and the spark plug fire. Rotating the crank backwards and then forwards like this takes out any slack in the big end bearing.

Loosen the magneto baseplate and rotate it until the points just open (light goes out or resistance goes to infinity). Fix the baseplate in this position. As these engines are governed to a maximum of about 1700rpm, a fixed advance is all that is required.

Finally reset the points gap to 0.50mm, replace the cover and flywheel. Because the magneto is on the inside of the flywheel on these engines, the air gap between the flywheel and the magneto is preset.

That's it for the timing. Fiddly, but once you get the hang of it, quite simple really. Hook up the wiring, replace the condensor if you have too and it's all done.



Timing cam and magneto mounting posts.



Points set and open at 0.50mm. Advance has been set.



Cover back on. This photo was taken prior to cleaning everything.

I didn't get any photos of the dial indicator in use, sorry. I guess I was carried away with the whole procedure as I've never had to remove the head to set the timing before

Next installment is the carburettor.

Chris

The carby on this engine is a simple governed, fixed jet unit with a float bowl and pressure primer. The only adjustments are for the mixture and idle and these are usually factory set. The other style of carby fitted to these engines is a diaphragm type. Diaphragm carbies will work better than fuel bowl types at higher angles of tilt, though unless you are mowing at angles greater than 45 degrees, there is no real difference. Fuel bowl carbies are a bit more robust (no diaphragm to rot) and all types of carburettor are sensitive to dirty fuel and fuel residue build up (varnishes) over time.

All I did with this one was to strip it then clean it in carby cleaner. I blew it dry then reassembled it with new gaskets and needle valve. I also cleaned the fuel tank and screen filter as well as the metal fuel line. I replaced all the flexible fuel lines and checked the fuel tap and primer.

The cable tensioning spring and governor spring were both OK. A new air filter (oil soaked foam type) was fitted.

I reset the two carby screws to about where they were and refitted it all to the engine.

When I started the engine and let it warm up to operating temperature, I opened the throttle fully and adjusted the mixture screw to the midpoint between too rich and too lean (the engine runs roughly at both extremes). I adjusted the idle screw so the engine idled at a reasonable speed. That's it.

The governor can be checked by moving the lever and making sure that the butterfly opens and closes (engine revs will rise and fall).

Finally, the two limiting screws can be set. These seem superfluous - maybe someone else can tell me what they actually do.



Cable and spring set up. Speed limiting screws can also be seen.



Throttle cable tensioning spring attachment.



Governor spring.



Wire link between governor and butterfly. Mixture screw on left and idle adjustment on the right.
The small pinhole above the float bowl on the body of the carby is used to check the carby.
If fuel is coming out of here, then the float is either not set correctly or isn't working properly.



Primer. This one was OK and only needed cleaning.


Chris

Finale.

I think that's it - or at least, that is all I did. The oil I used was a standard mineral 20W50 engine oil.

I must say that this engine is quite well designed and built. It may be overdesigned for its intended purpose though and that may contribute to it's reputation. The fuel will have to remain very clean and the timing spot on for it to perform to its maximum.

Over the years I've rebuilt many car engines (mainly Italian ones) and setup many carburettors (mainly multiple Webers) and this little motor is quite impressive. I had a lot of fun stripping, rebuilding and reinstalling it.

Excluding my time, the overall cost was

Gaskets $8.50
Points $4.20
Carby parts $3.60
Rings $17.40
Seals $6.30
Bearing $14.00
Air filter $2.30
Muffler $9.40

About $63 all up. Money well spent, particularly if it goes for another 30 years.

The decals for both the engine and the mower base cost about $12.00.

Here it is mounted on the refurbished base. I've still got to fix the catcher - it is rusty, but reparable.






At some stage I'd like one of the other forum members to read through this longish thread and check to make sure that I haven't made any obvious errors.

I'll try to upload the manual in the next post, but it is a little over 2.5Mb and I'm not sure of the upload limits on this bulletin board.

Happy mowing to all,
Chris

The manual won't upload as it is a pdf (2.5Mb). If one of the moderators could tell me how to do it, I'll happily post it.

Chris

You can upload a PDF of up to 2.86 MB. Just press the "Switch to full reply screen" button under the posting window, then click on File Manager.

That engine is a thing of beauty, by far the prettiest rebuild of a Kirby-Lauson I've seen. Your pictures and explanations are excellent - I think this will be a very useful thread in the archives.

Five comments on your explanations.

First, I think 1,700 rpm is the Lauson's idle speed, not its maximum, which is probably about 3,000 or so. The fixed ignition timing is a shortcoming these engines share with Briggs side valve engines: it is set so that the engine will not kick back during starting, and is then hopelessly retarded for maximum power. Honda avoided the problem by using a truly massive cast iron flywheel together with a decompressor, then were able to use a static timing of 26 degrees BTDC on their OHV engines, compared with just 6 degrees for Briggs side valve engines. In reality low compression side valve engines have slow burn rates and actually need even more advance than the Honda OHV has. Briggs decided, quite sensibly, that making the engine light and cheap was way more important than making it powerful, because people who want more power can simply buy a larger engine. (Also, the SAE power test procedure all the manufacturers use allows them to optimise the ignition timing during the dynamometer test, even though production engines then have much lower power output than they advertise, because they have a fixed advance of only a few degrees.)

Second, your governor spring has had the final gong and should be dragged off-stage by the proverbial shepherd's crook. It is supposed to be a close-coiled spring, and once stretched, cannot be recovered to a state where it will have the correct characteristics.

Third, the high and low speed screws restrict the movement of the governor arm to set the maximum and minimum governed speeds. The minimum is probably not important since the idle speed is set by the idle speed screw on the carburetor throttle butterfly valve, though setting it on the governor as well probably helps keep the transition smooth. The high speed setting is important because it controls the maximum speed the governor will allow the engine to reach. After all your good work, it would be a pity if the engine tried for 5,000 rpm and fouled its britches in the process.

Fourth, I looked up the Lauson engine specifications here:
http://lausonsmallengines.com/literature/specifications/tecumseh/H.PDF
That states that the H30A has a pneumatic governor. The Kirby Lauson has a mechanical governor.

Fifth, a very fine point of procedure, usually of no importance: anti-friction bearings, whether ball or roller, are conventionally installed with the type number facing outward, so people can see the type without removing it. (Tapered roller or angular contact ball bearings have to be installed to carry the thrust in the required direction, of course, regardless of type number locations.) For a jolly and entertaining read of myriad trivia of this ilk, see the Honda Common Service Manual, all 393 pages of it, available as a free download from here:
http://www.vf750fd.com/vf750f/Honda_Common_Service_Manual.pdf

If you would rather not have these comments in your thread, just PM me and we can find a solution. Because you wrote such an excellent thread, I've applied an extremely tough standard of "marking".

Thanks for the above commentary and no, I don't mind at all. Harsh 'marking' doesn't bother me as long as it's fair, and this is all fair.
I invited editorial comment and if it is available to all then my errors are corrected as they should be.
I guess in my defense, I did a lot of the work afterhours and may have been a bit tired. Still, I had a lot of fun and managed to take a lot of informative photos - some a bit too informative

The literature I had didn't distinguish between the H30 and the H30A which is why I put the A in brackets. There is virtually nothing available for Kirby engines so I had to use what I could out of the Lauson and Tecumseh publications.

I'll try to get a new governor spring - on reflection, it is knackered

The upper limit screw was reset to where it was prior to disassembly, so I hope it is correct. I'll try to measure the engine speed sometime and yes, 1700rpm will be the idle speed.

The pdf has been uploaded.

Cheers,
Chris

Mr Bonnar I have just had a quick look thru your exploits with Kirby engine etc . I have not visited this site for a long time and did not know that you were working on this engine.
I was a Kirby Dealer way way back and I have just had quik look thru the shelves here for a folder that contains all of the engines in the Kirby range for that period anyway.
I will have another look a bit later on as it is now 7.04 and I have to depart elswhere but I will check out the folder for this engine and can scan it for you if it wil be of any interest BTW While having a quick look I came across an oposition brochure for the Webb range of mowers dated 1981 Cheers for now Joe PS Had to go quickly at 7.04 .Just got back here and have corrected the typos Will have a look back thru the Kirby stuff just now. You have been pretty good at tracking down the parts you needed to overhaul the motor

Hi Joe, it's good to hear from you again.

There doesn't seem to be much information around regarding Kirby Lauson engines - the Tecumseh overhaul manuals for the original Lausons are not bad but cover a whole lot of models in one volume, so you have to work pretty hard to sort out what is specific to the ones Kirby assembled in Australia. There is an old Gregory manual that covers the Kirby specifically, and it is useful, but not very detailed in a number of areas.

I hope you are well, and will find the time to drop in as often as you can. Your knowledge is irreplaceable - I wish I knew as much about these engines as you do.

Joe,

Thanks - I'd be very interested (as would a lot of others no doubt) in any material on the Kirby engines. My 'hobby' background is automotive and I'm new to mowers, though the principles are similar. Because of the heritage involving three companies, it's difficult to get the correct information and most of it comes from assumptions made using similar engines as templates, in this case, the Lauson ?H30A and the Tecumseh H30.

I'm slowly getting there though and in the hunt for parts, the Americans have been very helpful and very patient. I owe quite a few of them many beers

Regards,
Chris

Thank you Mr Bonnar! A very timely and handy download that!
John

Hi Just read the last 2 post in here. Running late again though, but just a few moments ago found some different stuff from Kirby, but not he folder with the engines in . I will come back after brekky and continue the search. Found a mint condition Scott Bonnar manual which I will send on to you Mr Bonnar if you do not have one It has the 16 inch model and the 14 inch. The 16 inch is fitted with a Kirby and is priced at 99 GNS so Also has a details of the edger attachment and strangely enough that has the price shown as LSD 9 Pounds Seven Shillings and six pence Will post it you Gratis

Thank you - that is very kind of you. Do you need my address?

I've just bought the edger attachment as a NOS item - still in the original box with instructions. I'll post a photo if anyone is interested.

Chris

There has been a picture and comments on this attachment in a previous thread, Chris:
https://www.outdoorking-forum.com.au/forum/u...n=6985&Words=edger&Search=true#Post35652

Despite the title, there is discussion on the SB45 device in the thread, as well as an illustration of the SB430 one. See post #3758

It looks quite dangerous and I seriously doubt whether I'll ever use it. Interesting artifact though.

Chris

Yes Chris I was going to look in your Profile to see if it was there. Just send it to me and I will post it on to you Cheers Joe

PM sent.