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Hap Waldrop
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A few months back I had a brother of a friend call me, he live a few hundreds miles away, and has a TR6, he had paid a local British car garage to rebuild the engine for him, and once the oil got hot, at idle it only had 15 pounds of oil pressure. So long story short he brought the engine to me to go back into and fiquire out why the oil pressure was low.
The first thing I did was purchase a new oil pressure regulator spring and rod and compare them to the ones in the engine, I compared the spring rates on both spring on my Rimac valve spring tester and saw no real differences there, thats was about the only thing I could do externally of the engine that might effect oil pressure so it was time to go inside and take a look. I removed the oil pan, took the oil pump out, took it apart and checked the clearences, it looked good and measure good, no problems there, it was new oil pump. Then I moved on to plastigaging a couple of rod journals and main journals, what I found was .0025"-.003" on the two rod journals I checked and .0035"-.004" on the two main journals I checked. This was enough to tell me that was too much clearence and for sure one of the culprits of the low hot oil idle pressure, I beleive they told me cold crank up oil presure was about 45 psi. The mechanic who built this engine, I don't beleive was very experienced in engine building, and from his notes and own amissions, basicly had the crank, which was standard polished, and never measured anything, not even plastigauged, the bores are still standard as well, even though this has nothing to do with oil presure, I needed to make measurments there as well to determine if the engine needed to be bored oversize, it has .003" piston to cylinder wall clearence and I think that is about the limit of what you can stay with and not over bore, so for now, no plans to overbore the engine.
I don't think the engine builder was neglegent, just a bit unexperiecned, I'd say that probably 90% of backyard rebuilds are done the way he did this one with little to no measuring, and probably 90% of the time it works out for the amatuer buider, but we pros can't take such chances with our customers, so that why we measure and blueprint these engines, to insure this sort of mis-step does not happen.
I would like to ask the group here with Triump 6 cylinders who have rebuilt them, what kind of cold oil pressure do you see, and also what sort of hot idle oil pressure do you see in your cars. Any other clearences you have would be appriceated as well, I paln on building the rods and main to .0015", and I am yet to check the connecting rod big end, and I fully expect to found them out of spec and part of the problem, I will resize them myself. Thanks
The first thing I did was purchase a new oil pressure regulator spring and rod and compare them to the ones in the engine, I compared the spring rates on both spring on my Rimac valve spring tester and saw no real differences there, thats was about the only thing I could do externally of the engine that might effect oil pressure so it was time to go inside and take a look. I removed the oil pan, took the oil pump out, took it apart and checked the clearences, it looked good and measure good, no problems there, it was new oil pump. Then I moved on to plastigaging a couple of rod journals and main journals, what I found was .0025"-.003" on the two rod journals I checked and .0035"-.004" on the two main journals I checked. This was enough to tell me that was too much clearence and for sure one of the culprits of the low hot oil idle pressure, I beleive they told me cold crank up oil presure was about 45 psi. The mechanic who built this engine, I don't beleive was very experienced in engine building, and from his notes and own amissions, basicly had the crank, which was standard polished, and never measured anything, not even plastigauged, the bores are still standard as well, even though this has nothing to do with oil presure, I needed to make measurments there as well to determine if the engine needed to be bored oversize, it has .003" piston to cylinder wall clearence and I think that is about the limit of what you can stay with and not over bore, so for now, no plans to overbore the engine.
I don't think the engine builder was neglegent, just a bit unexperiecned, I'd say that probably 90% of backyard rebuilds are done the way he did this one with little to no measuring, and probably 90% of the time it works out for the amatuer buider, but we pros can't take such chances with our customers, so that why we measure and blueprint these engines, to insure this sort of mis-step does not happen.
I would like to ask the group here with Triump 6 cylinders who have rebuilt them, what kind of cold oil pressure do you see, and also what sort of hot idle oil pressure do you see in your cars. Any other clearences you have would be appriceated as well, I paln on building the rods and main to .0015", and I am yet to check the connecting rod big end, and I fully expect to found them out of spec and part of the problem, I will resize them myself. Thanks
