Engine rebuild?

[Keith Andrews]

I have also been checking out Outboard motor pistons
Got this reply back from a friend in that trade
"Have had a quick search of model specs and found that a 40 yamaha has a
similar size.
40x models have a piston dia 79.910 to 79.934 with pin 19.895 - 19.900.
Is the only one even close.

Regards

Graeme Doree,
Parts Manager.
Kev & Ians Marine Services,
Cnr Mahia & Holmes Roads.
Manurewa
Auckland. N.Z."

Anyone able to check out deisel engines?
These have thick tops that could be turned down...

General specs looking for
79.4 mm diameter
Compression height
45 to 49mm
Gudgen pin about 3/4 inch
preferbly flat top or dommed

keep in mind the gudgen pin could be off set a couple mm

Just got hit with a dose of flu, and peaking at the moment...so next couple days got a catch up on work before getting back into it.
Engine/parts goes into stripping tank so should be back for next weekend.

I would like as much info/in put as possible before Neil Moore gets back after the 27th for his expertise input.

I want to do this once, do it right....soon
The engine in the braddy at the moment has 40+/1000 piston slap and there is one noisy gudgen...there is almost as many fumes coming out the breather as there is the exhuast.

Steps

[Bryan Walker]

Have a look at http://www.jccpiston.com


some of the VW pistons may work?

[Keith Andrews]

Good site..I have contacted them
VW....the compression height is too small

[Keith Andrews]

Compression
Im getting myself mixed up...or something is wrong???

Stroke of 101.4mm Bore 80mm (actual stock 79.4)
That gives 503cc/cylinder or 2 cylinders 1006cc Right?
Engine is rated as 1005cc
Is not a engine rated at total volume, not swept volume?

I have cc ed the head chamber and cylinder volume piston at the top of the the stroke.
Head volume 54cc
Cylinder combustion volume 72cc
Gasket volume
Area of head gasket= 75.5cm sq
Compressed thickness =1mm
Volume head gasket = 7.5cc

Therfore the total combustion chamber= 54+72+7.5= 133.5cc
Total swept volume= 503cc
Total cylinder volume 133.5+503 = 636.5
Therefore the Bradford is a 636.5x 2 = 1273cc Engine
NOT a 1005cc

Now actual Compression ratio
one 1 cylinder
Total volume= 636.5cc
Combustion chamber 133.5cc

That gives ratio of 4.77:1 compression ratio
NOT 5.4 as per factory.

This is good and bad news
Bad news..old saying "cant beat cubes for power" or start decking / planing reduces cubes...as does dome pistons
Good news....we have more room to work, without dropping below 1000cc, even better if oversize.

What we have to work with
Leaving the gasket thickness out, simply as a built in clearance factor of 1mm

Increasing combustion ratio by decking
Closed Valves are level with deck (assuming not ressessed in)
If resessed back in can pick up 2mm off the deck
This gives 15cc
Total volume would be 641.5cc
Combustion volume (including gasket) 118.5cc
Combustion ratio 5.4:1

Increasing combustion rato by head planing (stock deck)

Outlet valve opens 6.2mm above the Stock deck
Head depth is 9.9mm
As the head is not recessed for the whole area of the combustion planning is diff to the deck being 55.1 cm sq.
Allowable to be planned
9.9-6.2= 3.7mm
This gives 20.4 cc
Total volume would be 616.1
Combustion volume(including gasket) 113.1
Combustion rato of 5.45:1

Combining the above is not straight forward as the valves would hit the head
We can resess the valves and deck 2mm as above (15cc)
AND plane 1.7mm off the head. (9.4cc)
Total of 24.4 cc
Total volume would be 612.1
Combustion volume(including gasket) 103.1
Combustion rato of 5.34:1

Increasing piston compression height, conrod length
Piston is 3.3 mm below the deck @top of the stroke.
Again calculated on stock deck/head.
Increasing the height of the piston 3.3mm, and using the 1mm head gasket for head clearance.
80mm diameter height 3.3mm =16.6cc
Total volume 619.9
Combustion chamber 116.9
Compression ratio 5.3:1

The max compression Ratio that can be achieved..
Recess valves flush and deck 2mm
Plane 1.7mm off the head
Total 24.4cc
Increase piston height 1.3mm 6.5cc
Total volume 605.6cc
Combustion chamber 102.6
Compression ratio 5.9:1

Thats not good either...Althu better than the calculated stock of 4.7:1

At this piont I do question, with all due respect, that planing and decking would cause extra loads on the crank causing failure. At these compressions it is just not realistic...IF this has been tried before, I would therefore have to suggest another problem (serious out of balance, poor machining, assembly, not using plasti gauge etc) caused any failure of the bottom end.
OR my measurements, calculations above are screwed lol
PLEASE can someone check and varify?...to many things are not adding up.

So rethinking....
essentually the total stock volume needs to stay stock (636.5cc)
The compustion chamber (133.5cc) needs to be reduced
How much?
A combustion chamber of 79.5cc will give a ratio of 8.0:1
A combustion chamber of 75cc will give a ratio of 8.5:1
For arguements sake I will use 77cc as target.
So need to take 56.5cc out of the head
Head volume is 54cc and needs much of the space for the valves.
Filling the slopping end of the head one can get about 22 to 25cc keeping a slope in that area.
This alone would up the ratio to around 5.8 to 6:0
Planing the head would then yeald approx another 20cc giving a ratio approx 7.0:1
Short of the targeted 8:1 but would be a very easy place to start.

Will talk to a few guys as to the best way fill in the head some what

If u have managed to read this far..thankyou....I have been typing notes here most of the afternnoon as I have measured, calculated etc.

Comments thoughts welcome...
Steps

[Bryan Walker]

the Volumeor displacement is only the cylinder not the head volume.

Displacement (cu.in./mm): Total cylinder volume, Calculated in cubic inches using the formula

.7853982 x bore² x stroke x number of cylinders.

To convert to cubic centimeters (cc), use the conversion factor of 2.54 for bore and stroke.

.7853982 x (bore x 2.54)² x (stroke x 2.54) x number of cylinders.

Bore x stroke (in.): Diameter of cylinder bore and length of piston stroke

i.e 60.4 cu in or 990.9 cc

60 cu inch as per 1946 data sheet

Bryan

Bryan

[Keith Andrews]

According to the manual for Bradford 1952
And Pitmans "Jowett. Javelin, Jupiter & Earlier Cars" pub 1959, data sheets
Bore 3 1/8" or 79.4mm
Stroke 4" or 101.6mm
CC rating 1005cc
7853982 x bore² x stroke x number of cylinders
Comes to 1006 cc or 61.4 Cubic inch
Pitmans round off to 1000cc and 61 cub inch

The part in my post that does worry me is the rated Compression ratio of 5.4:1 but the REAL ratio is 4.7:1
We may as forget about pump gas and run on kerosene

[Bryan Walker]

Sorry Keith,
Don't know were my calc from cu inch to cc went wrong? doing it late at night could have something to do with it.

Did you take in account of piston from the deck to the top compression ring, in your calcs?
IE the deck height volume was calced or measured. if fluid measured and the stroke cc was calculated this would create an error in the CR.

Bryan

[Keith Andrews]

doing it late at night could have something to do with it.

LoL m8 all that above was done late at night...thats why Im questioning some of it myself lol

Did you take in account of piston from the deck to the top compression ring, in your calcs?

OI should have explained my method
1/A barrel, with piston in, ring sitting on the ring lip and valves sitting in seats ...rings valves have a light film of grease to seal.
The ballet is made level, perspex over the top and water measued in with a burrette thru a hole.
2/The head ...the same process
3/To get the theretical volume of the gasket/head and deck planing, 1mm graph paper is impronted. Volume is area of the basex height, except for a tiangle.
4/The postions of the valves in relation to head/deck is established with palercine impressions.
5/To get approx volume to fill head in, it was tilted and then filled with water from a burette.

I have planed heads and stuff but only on small block chevy, so Bradford is new terriotory.
I have never added into a combustion chamber and my metology in this area is some what....no nil lol
What if I bolted the head down to a template to stop to much warp. Then heat with a gas axe to pretty hot....then started to fill in with mig...keeping heat fairly constant. let cool, grind and shape/finish for a good fuel flamet....... have it crack tested and planed.
I do have a lot of old heads laying around.

Would that work?

[Bryan Walker]

Neil would be the one to ask - if he is back yet.
I'd go for trying to lower the cylinders compression area first before playing around with the heads combustion chamber as you will open up a very large can of worms far as getting good fuel mixture, even combustion etc even with the Edwardian design of the braddie's engine.

You've left off 1 more simple answer to raising the CR and that is to use a small blower!

[Keith Andrews]

Neil would be the one to ask - if he is back yet.

GOOD idea lol, will ring him in a few minutes...I think he said the 27th so hes had a couple days to rest lol

You've left off 1 more simple answer to raising the CR and that is to use a small blower!

Now u are talking...Bit of nitrous to? lol

[Keith Andrews]

Had a great chat to Bryan last night...
He pionted out that with the piston crown raising above the bores, into the compression chamber will alter the compression figures I have given in above posts.
The piont of error is :
When the piston is at the top of the stroke, the piston crown takes up some of the compression cnamber...
This has been calcuted for in the above measurements.

Therfore the volume of the piston hast to be removed from the swept area as the top of the swept area is from the top of the ring not the top of the piston.

Good news is:
I have remeasured the crown volume, the volume makes very little difference to the figures in the above post, at most 0.06:1 on the compression ratios. There is not enough to make the measured 4.7:1 compression ratio come up anyware near the Jowett spec of 5.4:1

Spoke to Neil a few minutes ago:
Migging the inside of the head chamber is not a good idea.
Best alternatives are:
1/ make up a plate to fit in and fix with screws/locktite
2/Fill with brazing
3/ Fill with cast iron welding rods

In the mean time over next couple weeks going to sort out new pistons barrels etc and get the engine assembled with stock heads....then return to this project.
1st plane a spare set of heads down 3.5 to 3.7mm and test
Then look at filling the head combustion chamber.

PS
I was suggested to mill valve resesses into the head to give more room for valves and plane the head more....The thickness in this area between combustion surface and water jacket is already at the minumium and any work in this area would seriously weaken the head.

[Keith Andrews]

Delay...was grinding the valve seats. there appears to be a crack thru from the inlet valve to bore...will get crack tested tomorrow...
Hopefully will have a spare bore here.???
New gudgen are on the way, got the new rings, hopefully will get reassembled next week, but following week are in Adelade, Aussie