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Wed Jan 11, 2006 8:59 am

quick question - is the cylinder hole in the case the same size between a 25 and 36 hp engine?

basically - can 36 hp p/c's be used on a 25hp motor?

Wed Jan 11, 2006 10:20 am

It is 'basically' the same case with only minor differences
-Craig

Wed Jan 11, 2006 11:31 am

They are both different sizes. The 25hp engine has a 75mm bore while the 36hp engine has a 77 mm bore.

Thu Jan 12, 2006 8:11 am

Hi sportee,
No, and no. The bore is differant, with the 25 HP cylinder OD being smaller.

Fri Jan 13, 2006 7:48 am

He's talking about the bore in the case, not the bore in the cylinder. I beleive it is the same. I can take measurements.

As for using 36hp Ps and Cs, not sure, but I do recall about people making stealth 25 hp engines out of 36hp cylinders and heads, and hiding them somehow under 25 tin.

Fri Jan 13, 2006 9:47 am

hey guys Just measured mine 25hp 74.24 36hp 74.90 later Mark Dearing

Fri Jan 13, 2006 7:29 pm

My 47 had 36 pistons inside the 25 cylinders, it ran this way for fine.
The owner back in the 50's had done this, it ran like this until it was taken off the road in the 70's. The orig case was never bored as it now back to stock. I still have the 36 bored 25 cylinders maybe I'll make a hot rod one day.

Sat Jan 14, 2006 7:43 pm

Holes in case are same size. Catch is holes in 25hp heads are smaller than 36hp heads (could go & measure if you want) & I recall cylinder wall where it seals to head will be very thin if you machine cylinders rather than heads when doing the stealth 36hp conversion.

I have to confess I retained the conversion as the kdf heads on my 47 had been done years ago. (Would require spacers to be made to go back)

There is no problem with clearance to tin or other things using the 36hp cylinders.

The 36hp heads will bolt straight on but will not clear the head tin as the head retaining nuts/inhex nuts are not recessed into head. The best stealth option would be to flycut 25hp heads to fit under original tin - if you can bring yourself to molest an original head.

Original jetting on carb seems to be fine with the bigger pistons and a little more discreet hp doesn't hurt. Have done about 10,000 miles with this setup in the last six years.

I have collected one Kdf head so far with a view to going back to 25hp.

Sat Jan 14, 2006 7:55 pm

the 25hp block has a smaller cyc OD than a 36 hp block the 36hp cycs will not go in the 25hp block they are larger on the outside

Sat Jan 14, 2006 9:47 pm

Yup walls were very thin but they held up for years with owner back in the 50-60's. The thing is if you have old worn out cylinders you could do this if your stuck for 25 hp parts.