TZ/RD 750 Project help

[pdxjim]

I agree the only way out at this point is to rebuild the mating surface with weld, then machine flat.

[mavguy]

Copper gasket. Fingers crossed.

[m in sc]

maybe im missing something here, but whats going to seal the combustion chamber? 

[mavguy]

maybe im missing something here, but whats going to seal the combustion chamber? 

The O-Ring
This is just to keep the water from leaking outside.

[Striker1423]

maybe im missing something here, but whats going to seal the combustion chamber? 

The O-Ring
This is just to keep the water from leaking outside.

Is the o-ring proud of the copper gasket?  Just asking as copper wont squish down like an oring will. O-rings squish flat to the mating surface.

Watch for any potential  burning coolant. Will smell sweet as well and burn white.

[Dvsrd]

The o-ring needs to be totally "enclosed" by the groove and the head. Unless the gasket thickness somehow is compensated for, the o rings Will burn.

[m in sc]

yup.

you're going to ultimately have to get those cyls modified one way or another. you lift the head with the copper gasket you'll extrude the o-ring in no time.

[Djg8493]

Is there a chance he could get away with a layer of three bond over the o rings to both close the gap and help prevent the o rings from burning? Assuming it sets air tight.

[m in sc]

thats a negative. it either needs to be a full copper gasket or repair the cyl and do it right, you cant hybrid it. the flame front will burn the rtv and o ring right out with that much of a gap filled.

[stresa]

I am in with the sceptical posts of most guys.
It will not work with the copper gasket.
There is a reason why all 3 or 4 cylinder watercooled conversions of RD/TZ based 2cylinder crankcases has either welded cylinders and heads like this one



or with special casted sole cylinders and heads like these



I am myelf in the process of building a 3 cylinder TZ engine and have 2 friends which built 3 and 4 cylinder RD based engined bikes. They used RD/LC cylinder for cost reasons,

Regards Uwe

[1976RD400C]

Agree about any gap with a O ring, immediate failure. You may be better off making both surfaces perfectly flat and spraying Copper Coat on it. I did that with a RD once and it worked ok. Not sure about your compression ratio though.

[Jspooner]

I would figure out how make o-rings work. To make the copper work you are going to have to bastardize the heads. You already bastardized the cylinders so I'd just keep working on those to make those work with o-rings.

[stresa]

Sorry,
I don't know why but did a double post and deleted the 2nd