I was recently given this engine as half of a leafblower - I understand that it's a McCulloch, at least that's what was written on the instruction book that came with it.

A couple of afternoons work and it looked like an airplane engine... I've done the following work:

Complete stripdown and clean
Cut off excess bits of casting from the crank-case
Made engine mount
Turned a prop-driver, prop washer, cut off and threaded the main shaft
Turned the fins off the front of the magneto flywheel
Exposed the (protected) needles on the carb for tuning
Screened the ignition lead
Opened up the muffler a bit by drilling out the outlet hole through both muffler chambers.

The engine runs fine, both on the ground and in the air. Starts by hand very easily. I've measured 6800 revs on a Menz 18x6 prop - that's what I'm flying it on.

But...

Is there anything else I can do to improve the engine? To my mind you can never have too much power or too light an engine...

I've considered packing the crank-case and crank-web. Is it worth it?

What about port timing? Any gains here? I'm certainly not new to petrol engines, but know very little about removing metal from the insides of them...

What else would you do to the engine?

Its not an original McCulloch. It's probably a Weed Eater 25? That's not to say it didn't say McCulloch on the outside case?

Did you put a bigger carb on? Can you open up the muffler?

In the picture is a McCulloch 32. I have a few of them

w8ye: What RPM do you get from your McCulloch 32? With what size prop? Would you say its smooth and powerfull? Thanks Capt,n

Philip,
McCulloch uses Weedeater engines in europe. In the states it is sold as a Poulan or Weedeater blower/trimmer. I think yours is a 25cc with a 10mm carb venturi. Remove the muffler and you may see a lip running all the way around the exhust port next to the piston. You may not have removed the exhust port liner yet. If so remove it to expose the lip. If you have the lip you can remove the cylinder and carefully file away the lip. I put a peice of cardboard(heavy paper stock) in the bore to protect the back of the cylinder. When finished, use a swiss file and fine sandpaper to remove the sharp edges around the port on the inside. This should give you more RPM. The stock port is very small.

Cheers, Dave

I have two 32's converted. The both have C-H and 12.7 Walbro carbs. One has had the cylinder/piston redone by TKG.

The unmodified one does 7400 with a 18-8 Dynathrust. The modified one does 7700 with a 18-8 Dynathrust.

They both have custom aluminum mufflers I got from Terry but I think he no longer has the type mufflers I have.

Looking at how the engines are made I would have thought the unmodified one would do better than my unmodified Homelite 30 but it was 100 rpm short. Their timing must be mild. I never measured it.

I recognise your engine... I used to have the 26cc that I bought already modified. I hated the exhaust retention...

The carb is stock, Although I have a spare, it's the same size. I'm reluctant to spend money on the engine, but if I come across a spare carb, I'll try it.

I'm thinking about doing a custom exhaust in ally, much bigger - and hopefully lighter.

Thanks

Thanks. I did notice the lip you mention. I'll remove it and see what happens...

While I've got the engine to bits again, are there any more internal mods I should think about?

Cheers

Philip,
The piston skirt blocks the transfer passages when at bottom of the stroke. Triming away the lower skirt at the wristpin ends corrects this. You see this in many model engines. A radius is needed releive stress on the piston. Here is a picture. I added a Zenoah G62 piston for comparison. I usually remove the rod, use masking tape to protect the uncut areas. You don't even have to remove the ring when using tape. I mark the area to be removed, drill holes at the corners. Then I use a dremel with a cutoff disk to cut away the remaining material. a swiss file and fine sandpaper finish the job.


Dave

I am sure this is a Mac also. I wonder if I could add a different bakplate and have 2 carbs on it. Carbs with maller throats with progressive linkage!!!!!! Capt,n Now...Get to Church...its Sunday!!!!!!!!!!!!!!

I've not started cutting metal from the inside of the engine yet, but have made an exhaust...

Flange from stainless steel sheet - took forever to cut - never again...
Bend from Krumsheld - I think - left over from another job.
Canister from the Pound Shop... Salt and pepper containers. There's a baffle 2/3rds of the way down the can.
Silver solder and pop-riveted construction.

4 1/2oz lighter than the exhaust that came with the engine, and has given me an extra 200 revs. A little quieter too I think.

As long as it stays together - my track record isn't good when it comes to making exhausts. It had 3/4 hour in the air today and is still in one piece... I'm keeping my fingers crossed.

Philip,
The muffler looks great. Is it supported somewhere along the body of the can? I think this is the secret to long life.

Hi, I am working on a McCulloch 28 now. I noticed your muffler is installed with screws. How did you install threads in the cylinder block? Could you take a photo of the job with the muffler removed? If you remove it.

Thanks George

Oldtimer,
There is some confusion here. Philip's engine is really a Weedeater 25 marketed under the McClloch name in europe. Weedeater 25 blower engines have screws holding the muffler on, unlike the Mac 28 and 32 in the US which use springs.

Dave

I kind of changed the design halfway through the job. Originally it was supposed to be a 2 part exhaust, with a flexi pipe between the header and the can. When I realised I hadn't got the right metal stock for this, I went with the simpler design in the photo. It's an odd looking exhaust... then again it's an odd looking plane, so I guess it suits.

The can of the exhaust isn't supported. I thought that since it's so light I'd try without a support. I'll see how it goes. In my experience, exhausts fail in the most unexpected way...

The Mac 32cc Pro Blower has bolts holding on the muffler too. Sorta hard to find though.

tkg,
I wonder if the typical Mac parts fit the case. If so it may be a nice upgrade.

Dave

Yep everything fits, sure makes the muffler thing much easier.

5505