Pietenpol-List: Back in the Air Again! (A-75 bottom overhaul)
Posted: Fri Sep 08, 2006 9:59 pm
Original Posted By: shad bell
Hi Folks,Well, after about 2 months of downtime we're back in the air again
I hadtorn down the A-75 back in July to investigate low oil pressure. Found very wornmain and rod bearings and a .010" / .010" under crank with mild scoring andtypical wear. The crank failed magnaflux due to a crack in the front main journalthat would not grind out at .020" under, but I located a good standarddimension flanged and yellow-tagged crank to replace it. The top end w/ chromecylinders was new about 65 hours ago, and all was well up there and within newassembly tolerances. Likewise for the oil pump. New gears had been installedwith the top end, and they were in excellent shape with good tip clearance.While looking for a crank I used the extra time to balance the pistons and rods.Found a total of 10 grams difference between the lightest & heaviest piston(spec is 13 max), but the two heaviest were within 1 gram of each other, whilethe two lightest were within 5. Rods were all within 4 grams, and I was ableto swap cylinders #1 and #4 to achieve less than 1.5 grams total imbalance betweenthe rear pair of pistons/rods, with about 4 grams total between the frontpair after mixing/matching rods.I finished the assembly last Friday before the holiday weekend. Used Hylomar alongwith the Continental thread to seal the case. If you haven't used Hylomarbefore, it's a non-hardening 100% polymer material developed by Rolls years agofor jet engine applications. Now used by Porsche, BMW, and more recently GMand Ford for metal to metal non-gasketed joints. I've never had a leak due toHylomar on quite a few VW's, BMW motorcycles, a few Porsches, etc.Completed the ground testing Saturday, no leaks & a clean oil screen, & drainedthe oil thru a paint filter with no surprises.First flight was Sunday, about 1/2 hour above the field, followed by another oilscreen inspection with no "findings".Now have about 1.5 hours on the engine, not a trace of oil on the exterior, oilpressure is back in the normal range and oil consumption seems to be low (toosoon to really tell yet) It also looks like the balancing paid off, as it ismuch smoother than before.I think the worn bottom end was allowing too much oil flow thru the main & rodbearings, resulting in much windage and oil loss thru the breather. I had addedthe breather extension tube last year, but it didn't help much. Still lost about1/2 quart/hour of operation, despite never filling the sump over 3 quarts.Now the oil level has not visibly changed in the one hour of operation sincethe first oil change Oil temperature is running 155-160F, about 20-25Fhigher than before. I think this is due to increased oil circulation to the headsbrought about with the higher oil pressure. All indications are good :-)Looking forward to some good flying this fall with renewed confidence in the oldContinental :-)Dave MordecaiPanacea, FLNX520SFHi Folks,Well, after about 2 months of downtime we're back in the air again I had torn down the A-75 back in July to investigate low oil pressure. Found very worn main and rod bearings and a .010" / .010" undercrank with mild scoring and typical wear. The crank failed magnaflux dueto a crack in the front main journal that would not grind out at .020" under, butI located a good standard dimension flanged and yellow-tagged crankto replace it. The top end w/ chrome cylinders was new about 65 hoursago, and all was well up there and within new assembly tolerances. Likewise for the oil pump. New gears had been installed with the top end, andthey were in excellent shape with good tip clearance.While looking for a crank I used the extra time to balance the pistons and rods. Found a total of 10 grams difference between the lightest & heaviestpiston (spec is 13 max), but the two heaviest were within 1 gram of eachother, while the two lightest were within 5. Rods were all within 4 grams, andI was able to swap cylinders #1 and #4 to achieve less than 1.5 grams totalimbalance between the rear pair of pistons/rods, with about 4 grams total betweenthe front pair after mixing/matching rods.I finished the assembly last Friday before the holiday weekend. Used Hylomaralong with the Continental thread to seal the case. If you haven't used Hylomarbefore, it's a non-hardening 100% polymer material developed by Rolls yearsago for jet engine applications. Now used by Porsche, BMW, and more recentlyGM and Ford for metal to metal non-gasketed joints. I've neverhad a leak due to Hylomar on quite a few VW's, BMW motorcycles, a few Porsches,etc.Completed the ground testing Saturday, no leaks & a clean oilscreen, & drained the oil thru a paint filter with no surprises.First flight was Sunday, about 1/2 hour above the field, followed by anotheroil screen inspection with no "findings".Now have about 1.5 hours on the engine, not a trace of oil on the exterior,oil pressure is back in the normal range and oil consumption seems to be low (toosoon to really tell yet) It also looks like the balancing paid off,as it is much smoother than before.I think the worn bottom end was allowing too much oil flow thru the main &rod bearings, resulting in much windage and oil loss thru the breather. I hadadded the breather extension tube last year, but it didn't help much. Stilllost about 1/2 quart/hour of operation, despite never filling the sump over 3quarts. Now the oil level has not visibly changed in the one hour of operationsince the first oil change Oil temperature is running 155-160F,about 20-25F higher than before. I think this is due to increased oil circulationto the heads brought about with the higher oil pressure. All indicationsare good :-)Looking forward to some good flying this fall with renewed confidence in theold Continental :-)Dave MordecaiPanacea, FLNX520SF________________________________________________________________________________Date: Fri, 8 Sep 2006 22:05:36 -0700 (PDT)
Hi Folks,Well, after about 2 months of downtime we're back in the air again
I hadtorn down the A-75 back in July to investigate low oil pressure. Found very wornmain and rod bearings and a .010" / .010" under crank with mild scoring andtypical wear. The crank failed magnaflux due to a crack in the front main journalthat would not grind out at .020" under, but I located a good standarddimension flanged and yellow-tagged crank to replace it. The top end w/ chromecylinders was new about 65 hours ago, and all was well up there and within newassembly tolerances. Likewise for the oil pump. New gears had been installedwith the top end, and they were in excellent shape with good tip clearance.While looking for a crank I used the extra time to balance the pistons and rods.Found a total of 10 grams difference between the lightest & heaviest piston(spec is 13 max), but the two heaviest were within 1 gram of each other, whilethe two lightest were within 5. Rods were all within 4 grams, and I was ableto swap cylinders #1 and #4 to achieve less than 1.5 grams total imbalance betweenthe rear pair of pistons/rods, with about 4 grams total between the frontpair after mixing/matching rods.I finished the assembly last Friday before the holiday weekend. Used Hylomar alongwith the Continental thread to seal the case. If you haven't used Hylomarbefore, it's a non-hardening 100% polymer material developed by Rolls years agofor jet engine applications. Now used by Porsche, BMW, and more recently GMand Ford for metal to metal non-gasketed joints. I've never had a leak due toHylomar on quite a few VW's, BMW motorcycles, a few Porsches, etc.Completed the ground testing Saturday, no leaks & a clean oil screen, & drainedthe oil thru a paint filter with no surprises.First flight was Sunday, about 1/2 hour above the field, followed by another oilscreen inspection with no "findings".Now have about 1.5 hours on the engine, not a trace of oil on the exterior, oilpressure is back in the normal range and oil consumption seems to be low (toosoon to really tell yet) It also looks like the balancing paid off, as it ismuch smoother than before.I think the worn bottom end was allowing too much oil flow thru the main & rodbearings, resulting in much windage and oil loss thru the breather. I had addedthe breather extension tube last year, but it didn't help much. Still lost about1/2 quart/hour of operation, despite never filling the sump over 3 quarts.Now the oil level has not visibly changed in the one hour of operation sincethe first oil change Oil temperature is running 155-160F, about 20-25Fhigher than before. I think this is due to increased oil circulation to the headsbrought about with the higher oil pressure. All indications are good :-)Looking forward to some good flying this fall with renewed confidence in the oldContinental :-)Dave MordecaiPanacea, FLNX520SFHi Folks,Well, after about 2 months of downtime we're back in the air again I had torn down the A-75 back in July to investigate low oil pressure. Found very worn main and rod bearings and a .010" / .010" undercrank with mild scoring and typical wear. The crank failed magnaflux dueto a crack in the front main journal that would not grind out at .020" under, butI located a good standard dimension flanged and yellow-tagged crankto replace it. The top end w/ chrome cylinders was new about 65 hoursago, and all was well up there and within new assembly tolerances. Likewise for the oil pump. New gears had been installed with the top end, andthey were in excellent shape with good tip clearance.While looking for a crank I used the extra time to balance the pistons and rods. Found a total of 10 grams difference between the lightest & heaviestpiston (spec is 13 max), but the two heaviest were within 1 gram of eachother, while the two lightest were within 5. Rods were all within 4 grams, andI was able to swap cylinders #1 and #4 to achieve less than 1.5 grams totalimbalance between the rear pair of pistons/rods, with about 4 grams total betweenthe front pair after mixing/matching rods.I finished the assembly last Friday before the holiday weekend. Used Hylomaralong with the Continental thread to seal the case. If you haven't used Hylomarbefore, it's a non-hardening 100% polymer material developed by Rolls yearsago for jet engine applications. Now used by Porsche, BMW, and more recentlyGM and Ford for metal to metal non-gasketed joints. I've neverhad a leak due to Hylomar on quite a few VW's, BMW motorcycles, a few Porsches,etc.Completed the ground testing Saturday, no leaks & a clean oilscreen, & drained the oil thru a paint filter with no surprises.First flight was Sunday, about 1/2 hour above the field, followed by anotheroil screen inspection with no "findings".Now have about 1.5 hours on the engine, not a trace of oil on the exterior,oil pressure is back in the normal range and oil consumption seems to be low (toosoon to really tell yet) It also looks like the balancing paid off,as it is much smoother than before.I think the worn bottom end was allowing too much oil flow thru the main &rod bearings, resulting in much windage and oil loss thru the breather. I hadadded the breather extension tube last year, but it didn't help much. Stilllost about 1/2 quart/hour of operation, despite never filling the sump over 3quarts. Now the oil level has not visibly changed in the one hour of operationsince the first oil change Oil temperature is running 155-160F,about 20-25F higher than before. I think this is due to increased oil circulationto the heads brought about with the higher oil pressure. All indicationsare good :-)Looking forward to some good flying this fall with renewed confidence in theold Continental :-)Dave MordecaiPanacea, FLNX520SF________________________________________________________________________________Date: Fri, 8 Sep 2006 22:05:36 -0700 (PDT)