Re: Yamaha rd350 road racer
I always do, but on the stock parts (I assume you are talking about the upper case to cylinder match) it doesn't matter so much. If you place the base gasket on the cylinder you will see quite a mismatch, but when you place it on the case you will see it matters much less or not at all. If you bolt up the empty top case to the cylinders and match up and/or alter the transfer ports then the stock base gaskets will stick out quite a bit into the transfers but if all the parts are stock then in most cases it won't matter due to the factory mismatch. It is REALLY important that the base gasket surface on the two parts is really flat and unmarked. If some hack has got in there with a screwdriver or chisel to pry the cylinder up (I've seen this a fair bit on RD's) you can have a lot of trouble. RD's have very little real estate to seal the cylinder base, and even a tiny bit of damage can cause a leak. Air leaking into the transfers can be quite terminal and very hard to discover if between the cylinders. If you suspect trouble, machine the parts flat and use a thicker base gasket to make up for the difference. As far as the port matching benefits in general goes, every little bit helps, but as a single item I think it a pretty small gain (of course this depends rather a lot on how bad the mismatch is and where). It is however free, and very little trouble to do so why wouldn't you? If you already have your bottom end together, I would match the gaskets to the cylinders and carry on.
I always do, but on the stock parts (I assume you are talking about the upper case to cylinder match) it doesn't matter so much. If you place the base gasket on the cylinder you will see quite a mismatch, but when you place it on the case you will see it matters much less or not at all. If you bolt up the empty top case to the cylinders and match up and/or alter the transfer ports then the stock base gaskets will stick out quite a bit into the transfers but if all the parts are stock then in most cases it won't matter due to the factory mismatch. It is REALLY important that the base gasket surface on the two parts is really flat and unmarked. If some hack has got in there with a screwdriver or chisel to pry the cylinder up (I've seen this a fair bit on RD's) you can have a lot of trouble. RD's have very little real estate to seal the cylinder base, and even a tiny bit of damage can cause a leak. Air leaking into the transfers can be quite terminal and very hard to discover if between the cylinders. If you suspect trouble, machine the parts flat and use a thicker base gasket to make up for the difference. As far as the port matching benefits in general goes, every little bit helps, but as a single item I think it a pretty small gain (of course this depends rather a lot on how bad the mismatch is and where). It is however free, and very little trouble to do so why wouldn't you? If you already have your bottom end together, I would match the gaskets to the cylinders and carry on.