Use new intake manifold with original exhaust manifold
Volvo PV, 121, 140, 200
29.12.2021In this instruction we describe how the exhaust part of an original manifold for B18/B20 can be reused with a new intake manifold. The original manifolds often crack at the bottom of the connection on the intake manifold side because the thermal stresses are very high there. This means bypass air on the intake side and dangerous mixture lean. A small angle grinder is required for this work. Please observe the accident prevention regulations. Wear safety goggles, and a dust mask is also highly recommended because of the grinding dusts produced. Never tilt the cutting discs when cutting!
We have had the manifolds for the Volvo B18A and B20A engines in our range for some time now as a reproduction, because there were hardly any usable used parts on the market, and they have not been available new for a very long time. Contrary to the original, our version is split, as was usually the case with the twin carburettor engines. The two-piece version eliminates the problem of thermal stresses between the two manifolds at the joint. These tensions inevitably led to corrosion of the original parts, mostly on the colder suction side. On top of that, the formation of vapour bubbles and the evaporation of the float chamber were naturally promoted by the strong heating of the intake manifold.
If the original manifold is only cracked on the intake side, then the exhaust side can still be used with a new intake manifold. They only have to be separated and that is what we want to show here. Other prerequisites are, of course, that the exhaust side is not warped and that the sealing surfaces are flat. However, if in doubt, you can have this reworked by any good engine repairer.
Clamp the old manifold properly in a vice so that it cannot twist under vibration. Then first cut off the two intake manifolds on the left and right under the carburettor flange. Do not cut the exhaust side! Do not try to cut off the intake part with a cut, this will either destroy the manifold or cause injuries due to jammed cut-off wheels. The described procedure should be followed!
This is what the interim result should look like.
Now cut off the carburettor flange with as much of the intake manifold as possible.
Cut off the remains of the intake manifold as close as possible above the exhaust manifold.
Then grind the intake manifold residues on the exhaust manifold with a roughing and flap disc.
This is what the result should look like in the end.
If appearance is important and further corrosion is to be avoided, the manifold should be sandblasted afterwards. A durable and corrosion-protective coating is, for example, flame spray galvanisation.
The manifolds are now ready for installation.
It does not matter whether you opt for a new exhaust manifold or cut off the original and continue to use it: The split version dispenses with the design disadvantages of the original. There are no problems with secondary air due to cracks and the car has far better warm start behaviour, not only in summer.
- All notes serve only as an example and do not replace the workshop instructions of the automobile manufacturers! All information is supplied without guarantee!
Additional information...
- 1080288: Intake manifold splitted Intake manifold