A Detailed Reply (Long) Part1
This is the reply I received from Dave Sharples who did much of the work on these glider tug conversions:
Firstly the 3.8 liter Ford V6 has done remarkably well, it first flew in 1992, we set the time between o?hauls to 1000 hours as it was revving out at 4800 rpm full throttle which is twice the speed of the 0-540 which it replaced. We run on a 2:1 ratio so at that speed it swings the McCauley 8452 prop at the same static rpm as the Lyc which was 2400, so the performance was the same. Fuel consumption dropped from 60 liters per hour (Lyc) to 34 with two extra launches per hour because of it?s faster letdown. Of course with the Lyc we have to be careful to avoid shock cooling as flying on the way up at relatively slow speeds around 60 knots gets the temps very high, then on letdown shock cooling occurs if the throttle is closed too quickly, we have cracked many pots. With liquid cooling we close the throttle immediately the glider releases and she is on the ground in no time. The coolant usually runs at max around 90 deg C (194 F) upon glider release the throttle is fully closed and as there is 15 liters of coolant to cool down it cannot happen quickly, when the temp reaches 70 C (160 F) the thermostat closes thus shutting of circulation.
As I said we limited the TIS to 1000 hours but at 900 hours it developed an oil leak at the timing case oil seal which requires removal of the engine so we decided to start the intended conversion to the LS1. (This will be # 3, one V6 and 2 LS1s)
The only defect experienced in flight was a broken valve spring that happened at 850 hours. That?s not too bad considering most of it?s life was at WOT sometimes on a long tow it may be there for 20 minutes or more. The V6 was carburetted using twin Su?s which were the only carbys that gave us equal fuel distribution throughout the entire range. The 3.8 liter V6 is a bit small for our operation and as I said worked very hard in getting the job done plus the problem of having several different pilots, many of them cowboys, not the usual private owner of a home built who rather ?pampers? his creation somewhat. So maintenance wise it has done remarkably well, an inspection of the bottom end revealed no measurable wear on crank journals at all, bearing clearances increased by .0005 ins. Bringing them up to .002 in, they were at a clearance of .0015 originally.
To try and get a bit extra power we fitted 1.8:1 roller rockers with heavier valve springs, this proved to be not a good idea as the cam bearings and timing chain suffered much wear, another example of how you create problems when deviating from manufacturer?s standard. Other than that it did remarkably well.
The re-drive was the old original Blanton one, terrible thing it was. At the first running period it failed at 10 hours, with modifications as things failed one at a time we got it to 20 hours then 50 then 100 finally not touching it at all in the last 300 hours, so there is not much left of it that is of ?Blanton? design. The two main problems we encountered were (1) keeping the bearings located into the drive shaft and (2) keeping the belt properly adjusted so as to keep it running central on the pulleys. The location of the bearings caused a lot of problems as they were located by ?Loctite?, no matter which high strength we used they eventually moved on the shaft. I eventually realized that we had the bearing inner cones ?loctited? onto a solid two inch prop shaft with the outer cones locked into the alumina housing, so with the expansion rate being so different between the alumina housing and the steel shaft they were locked onto something had to give, which happened to always be where the bearings were loctited onto the shaft and the inner cone then spun on the shaft.. So to alleviate this problem I made the outer cone of the bearing a sliding fit in the alumina housing grinding a small grove in the outer cone then locating it with a ball and grub screw to stop it turning but it could move laterally enough to compensate the expansion. To make things more positive I found an engineering bloke who ground a key way in the shaft and a shallow one in the inner bearing cone so turning was not possible should the loctite come loose. We had no more problems.
Then in #2 problem the belt always ran forward and rubbed on the front guide. This happened even when the pulleys were set exactly with an inside mic. So I then realized the horizontal line up must be out so I then put adjusting plates and screws allowing the pulley to be moved left or right and with trial and error we got it running very well. The pulleys and belt have been faultless, the belt manufacturers (Gates) said their belts had a shelf life of 10 years, so when the original had time up I replaced it, not worth the risk when only $160.00. Comparing the old belt with the new showed no visual wear, it was hard to pick which was which. The pulleys do have some slight wear but there is a lot more hours in them yet, don?t think I would positively say there is 2000 hours in them at this stage although Johnny Lindgren claims he has one now done 2000 hours which he recalled for examination and found no appreciable wear in belt, pulleys and bearings, says he sent it back as is for further use. I think proper anodisation is the answer here. I rather favour belt drives as they eliminate gyroscopic loads on the crank and there appears enough elasticity in the belt teeth to take out damaging impulses. Shame Johnny Lindgren has given it away he had a good product but I believe someone else has picked it up and will continue production of his excellent re-drives. What we have to realize here with glider tugs is that a landing and takeoff takes place about approx every 6 minutes there is a lot of time running on a dusty strip so this would not help the pulleys either, so 900 hours, mainly at 4800 RPM and not always in dust free air has been a good test one would think.
