Beware The Ultraseal
During a recent engine build process we nearly made a big mistake. The engine being put together was a Ferrari 308 GTB which has steel wet
liners in an aluminium crankcase. The liners sit on an annulus step in the crankcase and there is a sealing area here which is notorious
for giving problems. We were advised to have the crankcase Ultraseal processed to prevent any problems in this seal area. So this was
carried out. As it transpired there was a client driven spec change to the engine whilst it was away being processed, so on its return
we had to remove the liners. This would be very difficult according to the machine shop who had advised the Ultraseal and got it done
for us, as the sealant medium would now be effectively gluing the liners into the lower bores in the block.
In fact the liners came out very easily. But that was when we spotted the problem. It seems that so much sealant had been pulled into
the water jacket area through leaks in the seal zone that the build up of the now set rubbery product were filling the bottom of the
water jacket, and critically the areas between two adjacent liners, causing what looked like quite effective insulation of the liner
from the coolant. If the engine had been completely built this would have caused a major overheating problem and probably many hours
of frustrating and expensive diagnostic time before we gave up and pulled the liners out to find the problem. A complete engine strip
down would have been required as the liner fit is just about the last thing that is done on any tear down and the first on a build...
My conclusion is a big change in our strategy and view of the Ultraseal process, back to seeing it as merely a remedial process to be
used as a last resort only on individual parts that have been identified as having porosity, and not now using it as a routine quality
For OEMs to use it as a routine quality enhancement seems to me to be utter madness, when in reality the HIP (hot isostatic pressing)
process is widely available, does not introduce foreign materials into the product and produces, particularly in the case of aluminium
alloys, a finished component that is as free from porosity as a billet machined piece. The cost implications cannot be significant;
it may even be cheaper to do than vacuum sealing.