Stag water pump

Attached are a couple of photos taken of a Stag Water pump. The guy that owns this Stag lives in Gippsland. He supplied the parts and paid an engine builder $9000 to rebuild his engine and this is the result. He was out driving the Stag to Mornington and the engine stopped firing. The end result was that the Stag was sent home on a flat bed. First thing noticed was that the distributor rotor button was not turning. The distributor was removed and the jack shaft did not turn. The timing chains and cam were turning. He rang me and I said to check out the water pump. When he removed the cover the attached photos tell the story. The mechanic did not allow enough clearance and did not follow the correct method of check for the gap. He had changed from a 6 vane pump to a 12 vane pump and did get a 12 vane cover. The jack shaft will have to be removed and the gears checked. I believe that the dowell had sheared also. The lesson here is to have your engine rebuilt by some one who knows what they are doing. Check your mechanic out. If an Elec Water Pump (EWP) had been fitted this failure would not have occurred. As most people know that 4 years ago the water pump on my Stag failed and I fitted an EWP. No more issues.

Interesting observation on the water pump clearence. It could be possible here that it was not set up correct but not the ultimate cause. I would also be interested to hear more background info. I can understand too high an oil pressure Chris being one cause of tight chains. Certainly did not know some oil pumps have a stronger relese spring. I have a few oil pumps and have yet to fit one to the engine and I will not be fitting an oil pressure gauge. How can I tell a 'stronger' release spring? JY Sorry to hear this sad but familiar story. Stag engine rebuilds are a specilaist job as there are pitfalls even for mechanics who are experienced on other engines. The engine design is unique but is surprisingly strong if rebuilt correctly. In this case, if the cause of the failure were lack of water pump clearance I would expect there to be scoring on the cover, but that doesn't seem to be evident. The marks suggest only very slight corrision between a stationary pump impeller and the cover as though it was standing a long time - perhaps the marks are previous to the engine rebuild. I have built a few stag engines and followed many anecdotes on the subject. These types of engine failure seem to arise either from timing chains that are too tight, or from failure of the spiral gear. Tight chains put excessive side load onto the jackshaft front bearing, which then siezes when it overheats and breaks down the oil film. One potential cause of tight chains is excessive oil pressure, which occurs when pattern oil pumps are fitted containing a stronger release spring. The high oil pressure puts tension on the chains via the hydraulic tensioners. My car had about 70 PSI until I changed the spring and now it runs abround 40 psi which is more typical for a stag. Spiral gear failure is rare but can be caused when the water pump shaft or jackshaft is replaced by a poor quality pattern part which has insufficient gear hardening. It would be interesting to hear some background information about the parts used, and how long the engine ran after the rebuild. Did it fail after a long run on a hot day etc. Proprietor, Stagweber