Increase Compression Ratio/Eliminate Head Gasket

[Doc Sprocket]

Not a worry. I'm just going to soak the carbon off.

As for the warp- initially, it wrapped right around the whole intake valve area. I was this close to grabbing my other head (Jeez- that sounded really bad...) and seeing if it was any better.

Wait a sec- wouldn't you WANT to do the port work before cutting/lapping the valve seats? Cuz I did- that way if I bump a seat with the dremel, I don't have to do the seat TWICE!

 

[OzFab]

Not a worry. I'm just going to soak the carbon off.

Ah, you've thought this through...

Wait a sec- wouldn't you WANT to do the port work before cutting/lapping the valve seats? Cuz I did- that way if I bump a seat with the dremel, I don't have to do the seat TWICE!

Yeah, that's what I was trying to say; clean the head before grinding, as you would port before cutting in valves...

 

[Mrbirmi]

Hi, I'm new here and was wondering why a machinist stone couldn't be used to true up the head and block?

Thanks,

Matt

 

[carter]

I'm sorry to necro the thread, but what tolerances need to be checked and how after doing this?

 

[Doc Sprocket]

Naturally, check for flatness (obv.). Wouldn't hurt to doublecheck valve clearance, too. Depending on engine, it wouldn't hurt to check piston clearance. Basically, if it moves proximate to the head, check it. Better safe than sorry.

 

[carter]

how do you check these things with the head on. Doesn't the head hide those things more or less?

 

[Russ2251]

how do you check these things with the head on. Doesn't the head hide those things more or less?

Pieces of modelling clay...strategically placed (assemble head to block) and measured after a few (2 minimum) rotations.
IF ROTATIONS CAN NOT BE ACCOMPLISHED...DO NOT FORCE!!! This would mean something is interfering and this mod will not work for you.

 

[dengieboy]

Hmm be careful guys remember your squish (the gap between the top of the piston at top dead center and the lowest part of your head some time this is the spark plug electrodes) this was a trick which we used well over twenty years back. i had a yamaha 50cc fizzy which would do 65mph with the standard 50cc bore and piston!. we did the same and removed the copper head gasket flatted with a sheet of glass and some wet and dry paper. We would the cut another barrel base gasket from some extra thin card this would be put back together then we would remove the plug and move the piston down the bore. Then you find a roll of lead pipe solder about 3mm dia put the end in the plug hole and then turn the engine over top dead center. This action squashes the soft lead solder which then was carefully removed and measured with a micrometer we it was a bit trial and error back then but we found for that type of engine the best squish you could do was about 2.5mm any more than that and the piston would strike the plug and leave a nice hole in the top of the piston. Back in the day when i was 17 there was not a 50cc bike that could beat me its all about getting that tiny little gap right

 

[Russ2251]

I am finally getting a chance to test this out on a 4 cycle OHV Tecumseh.
Specifically, an OHH55-69071C.
Lapping has been completed. All that is needed now is to bolt up and double check clearances.

 

[Russ2251]

Well, it was a disappointment.
The good part was that the head and block had almost no warp at all, compared to Lawn-Boy model E and Briggs 5hp engines.
When assembled, the piston just bumped the head necessitating the need for a gasket.
Original Tecumseh head gasket is ~.035" thick. So, using a .010" thick gasket would yield the same thing as milling .025".
My goal is to eliminate gasket completely with minimal work.
A friend suggested that I remove metal from the piston crown or chamfer piston circumferance.
I think not.
I prefer to keep things simple.
As a result the Tecumseh will remain unmodified.

Next attempt will be on a Jacobsen J-321 2 cycle.

 

[landuse]

Well, it was a disappointment.
The good part was that the head and block had almost no warp at all, compared to Lawn-Boy model E and Briggs 5hp engines.
When assembled, the piston just bumped the head necessitating the need for a gasket.
Original Tecumseh head gasket is ~.035" thick. So, using a .010" thick gasket would yield the same thing as milling .025".
My goal is to eliminate gasket completely with minimal work.
A friend suggested that I remove metal from the piston crown or chamfer piston circumferance.
I think not.
I prefer to keep things simple.
As a result the Tecumseh will remain unmodified.

Next attempt will be on a Jacobsen J-321 2 cycle.

Thanks for the feedback Russ

 

[jwnoord]

We did a combination of that, ported the intake port (severly) and ran a harley 125 carb on our Briggs and stratton 3hp. Thing would not blow up! we got it as kids fter it was discarded on the farm as a water pump motoer that wouldn't start. Complete rebuild at school Ag mech class. We burned 125 Octane racing fuel, ethanol and methonol in that engine and it ran great. Would spin the tire taking off in gravel (centrifugal clutch) and the put out a orange cone flame from teh straight pipe.

 

[jwnoord]

We used Dad's air die grinder for porting heads on big blocks. Conical/oval shaped carbide cutter kind of shape / size of a cockel burr with a helical cutting tooth profile.

Works great on aluminum. leaves it relativly smooth but not pollished so you get some fuel/air turbulence.

 

[Doc Sprocket]

Well, it was a disappointment.
The good part was that the head and block had almost no warp at all, compared to Lawn-Boy model E and Briggs 5hp engines.
When assembled, the piston just bumped the head necessitating the need for a gasket.
Original Tecumseh head gasket is ~.035" thick. So, using a .010" thick gasket would yield the same thing as milling .025".
My goal is to eliminate gasket completely with minimal work.
A friend suggested that I remove metal from the piston crown or chamfer piston circumferance.
I think not.
I prefer to keep things simple.
As a result the Tecumseh will remain unmodified.

Next attempt will be on a Jacobsen J-321 2 cycle.

I just made this discovery and popped into this thread to remind everyone to carefully check clearances when attempting this. I'm working on a Tecumseh HS50 and discovered the very same thing. At TDC the piston comes proud of the deck height by a few thousandths... This would have been a fatal mishap had I not checked it first.