Engine rebuild and power mods

[luke1987]

Pocketing the pistons does sound like the way to go mate and then try timing it up again.

 

[solarman216]

Yep that is the route I would go, as clearly you are looking for most oomf possible, just make sure you give the valve at least 12 thou clearance, that way if the tappets are set at less than the 12 normal you will have a reserve space, good point is as this is the inlet you do not really have to take spring bounce into consideration as it is a positive downward force from the cam that is the problem as opposed to lack of spring return as on the exhaust valve, if I make sense that is as now several scotches down the line, Rick

 

[makeitfit]

Pocketing the pistons does sound like the way to go mate and then try timing it up again.

I have some old pistons here and will do a practice run. Those leaf like shapes on top of the pistons, are they serving any purpose ?

 

[luke1987]

The contours in the top of the piston are to aid the flow of the combustion gases as they exit the pre-combustion chamber some td27 industrial engines dont have them and just have a flat top piston.

 

[solarman216]

The contours in the top of the piston are to aid the flow of the combustion gases as they exit the pre-combustion chamber some td27 industrial engines dont have them and just have a flat top piston.

Better compression ration then, possibly better starting, unless there are other differences as well? Rick

 

[luke1987]

I think the majority of the industrial/forklift units were non turbo hence the flat top and higher compression.

 

[makeitfit]

Found an old piston and conclude it's min crown thickness is 12mm
I'll only need about 2 of those.
The next time you see this, I'll have chewed it into submission.



Hinge hole cutter too small by the way Rick, but reamer action on the router is my thinking. Template making to follow :naughty

 

[solarman216]

Are you sure 2 mm is enough, cutting it rather fine I think, I would be going the valve seat reducing, just my thoughts, Rick

 

[luke1987]

Cant take 2mm out of the seat Rick they wouldnt last and you would end up with awful recession. Hence why you pocket the pistons.

 

[solarman216]

Cant take 2mm out of the seat Rick they wouldnt last and you would end up with awful recession. Hence why you pocket the pistons.

Thanks for that Luke, this is a new area for me, never got involved in tuning with cams and the like, Rick

 

[makeitfit]

Right then about this piston pocket thing
Been a few weeks but some hours presented themselves today :clap
First off I made up a plywood template as accurately as possible .
Used steel rule and vernier gauge etc , head gasket and head. Anyway made this up and as best I can measure it's sub mm accurate :thumbs

After some time and drilling and that I got this on test rig.

It's located on the 2 stud positions .
I've drilled many holes to suit the head bolts so I'll be able to bolt the template down in many positions away from the router.

This took about 20 minutes of nerve racking work , probably only removing .5mm at a time.
First attempt not too bad and 3mm deep. Caught a few alu chippings that scared the surface.

Took a bit of emery paper and finished it off by hand
Next stage is to mask up the block and try the real thing :naughty

Onwards

 

[solarman216]

O M G, I hope it will be worth the effort, Rick

 

[makeitfit]

O M G, I hope it will be worth the effort, Rick

Who knows, but I really didn't want to take the engine out again :lol

 

[luke1987]

Hats off to you Pete that really is a great bit of engineering. Keep us posted.

 

[rayf3262]

Fly cutting in situ?
https://youtu.be/5wk7gbGWPN4

 

[solarman216]

Fly cutting in situ?
https://youtu.be/5wk7gbGWPN4

This one comes into its own as the valves are at an angle, I like Petes method for straight cut, Rick

 

[macabethiel]

Valve Clearance Hole !

Gulp,......... I guess you will be turning the engine over manually with no heater plugs /and/or injectors in place to stop compression making turning easier when the head is back on before you try and start her up - just to be on the safe side ?

 

[makeitfit]

Gulp,......... I guess you will be turning the engine over manually with no heater plugs /and/or injectors in place to stop compression making turning easier when the head is back on before you try and start her up - just to be on the safe side ?

Oh for sure. I've done one dry build to test clearances hence this extended task :thumbs

 

[makeitfit]

Is there a DIY method of calculating the reduced compresion ratio ? Obviously by removing some material the CR will go down a bit but is it significant ?
Thinking more boost but harder starting as Luke suggested :nenau

 

[macabethiel]

Not much loss methinks in real world

Back in the day when I tuned petrol engines 15 thou off the cylinder head would make naff all difference.
It needed a change from recessed pistons to flat tops on a Cooper to make any impression. A bit of carbon will help when the machined surfaces turn black again.