Wear makes it looser. Post 96 said that with cam only installed it is tight. That suggests an oversize replacement cam. Check the cam journals with a mike and compare with book value and original cam.
Post Conversion - Crank Rotation Tight
- Thread starter Tuneturkey
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As Hot Wings said, most VW problems are the result of overheating and improper torque values. Correct again.
When I bought my first new VW in 1969 for $1868, the salesman told me to not lug it down in the gears like driving a V-8, and if I did, don't expect the engine to last very long. Said, since the fan is driven off the crankshaft that low rpms is low cooling. Shift the gears on the marks on the speedometer, that is what they are there for and the engine will be cool and happy.
When I bought my first new VW in 1969 for $1868, the salesman told me to not lug it down in the gears like driving a V-8, and if I did, don't expect the engine to last very long. Said, since the fan is driven off the crankshaft that low rpms is low cooling. Shift the gears on the marks on the speedometer, that is what they are there for and the engine will be cool and happy.
I would think the cam would wear itself into the warped case unless the engine stopped and seized the instant the case overheated.
Or, Hot Wings post 88 explains how the parting face can wear and effectively reducing the bore size. So the old worn cam might fit but a new cam might not?
Or, Hot Wings post 88 explains how the parting face can wear and effectively reducing the bore size. So the old worn cam might fit but a new cam might not?
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Thanks all for the input! Very educational at the very least.
Remember, also, that this is a 1/2VW Better-Half engine. has a full case, but crank and CAM have been cut eliminating the shafts past the middle, main bearings (#2, I think, #1 being flywheel).
Last dis-assembly revealed discolored lubricant on the middle bearing along with rubbing on the bearing. Since the bearing is already scratched, I am tempted to do some grinding on the bearing at the wear points to see if a couple of mm will make a difference in tightness. As mentioned in earlier posts, the wear pattern on the full bearing is off center of the case parting line. considering the parting line as 0 deg. the wear is at CW 20 deg, and 200 deg., leading me to believe that the bearing saddle is oval shape, narrowest at 20 and 200 deg, longest at 90 and 290 deg.
Presently working on having the CAM saddles measured accurately at a machine shop, necessary repair to follow. Thanks to Pops and Fly2Kads for recommending shops closer to home.
Johnc
Remember, also, that this is a 1/2VW Better-Half engine. has a full case, but crank and CAM have been cut eliminating the shafts past the middle, main bearings (#2, I think, #1 being flywheel).
Last dis-assembly revealed discolored lubricant on the middle bearing along with rubbing on the bearing. Since the bearing is already scratched, I am tempted to do some grinding on the bearing at the wear points to see if a couple of mm will make a difference in tightness. As mentioned in earlier posts, the wear pattern on the full bearing is off center of the case parting line. considering the parting line as 0 deg. the wear is at CW 20 deg, and 200 deg., leading me to believe that the bearing saddle is oval shape, narrowest at 20 and 200 deg, longest at 90 and 290 deg.
Presently working on having the CAM saddles measured accurately at a machine shop, necessary repair to follow. Thanks to Pops and Fly2Kads for recommending shops closer to home.
Johnc
Just curious, what would happen if you smeared that cam journal with some lapping compound, put the cam in the case, torqued it up, and then spun the cam a bunch to clean up the tight spots? My thinking is that the lapping compound will take away a lot more of the softer stuff (the aluminum case bearing surface) than harder stuff (the iron cam journal). But I've never tried this on an engine, only motorcycle transmission gears with bronze bushings riding on hardened steel shafts.
I considered that. But usually the lapping compound needs to be replenished a few times so retorqueing the case time is a pain. The clearance should be .001" min or .003" max new (Cont. A-65 spec.) or .005" service limit. Limbach (VW) new cam is 24.99-25.00mm. Bore is 25.2-25.04mm
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TFF
Well-Known Member
Is this the original cam that is cut down, or one that is bought for this motor? If you have the old cam, put it in, even if you don’t have bearings for the last journal. If that spins...
Good morning from Baton Rouge, and it is a Good Morning.
Three cheers for the home team, the case is closed torqued and rotates freely!!! Hip hip horray!!!
The last closing was #8 and my old fingers are tired, and very dirty!!!
Found an older fellow here locally that was born in a VW waggon when they came out, and before plastigauge, and he was full of how too's for the problem. Many the same suggestion as provided by you guys. Namely, he had faced the same problem numerous times in old days, and was working on an engine when I called him. Had never heard of a tool to clean out the cam saddles with out oversizing them.
After many questions, his first suggestion was " if you can turn it at all, then the CAM is probably only a few thousands off, so work on the cam bearings, and polish the cam surfaces slowly, also take off a little material from the saddle. Sounds familiar? He also mentioned that new CAM thrust bearings come large and will drag on the CAM, so they have to be ground down and polished. Didn't think that was an issue, but it helped.
After maybe 5 times, closing the case, assess the change, open polish some more, close case and try again, with the crank in place the combo would spin like s bicycle wheel. This morning, I decided that it was time to put in the crank, sealer, close the case and get it up to 25#, following a sequence that favored the outer small bolts, those away from the case bolts closest to the CAM. With all those in place and up to 10#. The crank/CAM still spun freely. Added the balance of the bolts at 10# still with no change, then got all to 15#.
Encouraged at that point, put the 12mm main bolts on one at a time torquing randomly away from the CAM area, No change in tightness at 10#, added rest of the main bolts and torqued to 15#, then to 25# with only a slight increase in tightness, but 100% better then at the beginning. Probably not absolutely perfect, but good enough to get the engine running.
Up until the last closure, I had been working with only the CAM installed, working to get it to spin freely with the case closed. My conclusion, is that torquing the case fully pulled it back into shape, especially the middle CAM bearing, and the polishing improved the fit.
My thanks to all of you that contributed your experience, wisdom, encouragement It was great having y'all on my team. I learned a great deal, including where to get advise. Will no doubt have many more questions before it is running, but I know I can count on y'all!
Thanks,
Johnc
Three cheers for the home team, the case is closed torqued and rotates freely!!! Hip hip horray!!!
The last closing was #8 and my old fingers are tired, and very dirty!!!
Found an older fellow here locally that was born in a VW waggon when they came out, and before plastigauge, and he was full of how too's for the problem. Many the same suggestion as provided by you guys. Namely, he had faced the same problem numerous times in old days, and was working on an engine when I called him. Had never heard of a tool to clean out the cam saddles with out oversizing them.
After many questions, his first suggestion was " if you can turn it at all, then the CAM is probably only a few thousands off, so work on the cam bearings, and polish the cam surfaces slowly, also take off a little material from the saddle. Sounds familiar? He also mentioned that new CAM thrust bearings come large and will drag on the CAM, so they have to be ground down and polished. Didn't think that was an issue, but it helped.
After maybe 5 times, closing the case, assess the change, open polish some more, close case and try again, with the crank in place the combo would spin like s bicycle wheel. This morning, I decided that it was time to put in the crank, sealer, close the case and get it up to 25#, following a sequence that favored the outer small bolts, those away from the case bolts closest to the CAM. With all those in place and up to 10#. The crank/CAM still spun freely. Added the balance of the bolts at 10# still with no change, then got all to 15#.
Encouraged at that point, put the 12mm main bolts on one at a time torquing randomly away from the CAM area, No change in tightness at 10#, added rest of the main bolts and torqued to 15#, then to 25# with only a slight increase in tightness, but 100% better then at the beginning. Probably not absolutely perfect, but good enough to get the engine running.
Up until the last closure, I had been working with only the CAM installed, working to get it to spin freely with the case closed. My conclusion, is that torquing the case fully pulled it back into shape, especially the middle CAM bearing, and the polishing improved the fit.
My thanks to all of you that contributed your experience, wisdom, encouragement It was great having y'all on my team. I learned a great deal, including where to get advise. Will no doubt have many more questions before it is running, but I know I can count on y'all!
Thanks,
Johnc
Winginitt
Well-Known Member
- Joined
- Apr 5, 2019
- Messages
- 176
One last thing you should think about. As you remove metal from a bearing surface you increase the clearance between the bearing and the part it is supporting. Increasing the clearance allows more flow at the cost of pressure (resistance to flow). Watch the attached video and notice how much difference a few thousandths may make.
Reduced pressure is the only downside of the Bob Hoover's HVX mods to the oil system for more flow to the side of the engine that has reduced flow to the head.
To increase the flow, the normal thickness of the oil pump cover plate, paper gasket is .004". I measured several oil pumps and they all had .0005 gap between the face of the gears and the face of the oil pump. So normally you have .0045" total clearance when using the stock gasket between the face of the gears and the inside of the cover plate. Bought some .0025 gasket material from NAPA and used the old gasket for a pattern. Raised the oil pressure from 32 lbs to 42 lbs with oil pressure at cruise RPM and 20 lbs at hot oil idle. The oil piston and spring on the flywheel end of the case is the high pressure release. Bought an aftermarket adjustable cap and set the pop-off pressure at 56 lbs. Few hundred flight hours ago.
He can do the same if he needs a little more pressure.
https://vwparts.aircooled.net/Oil-Pressure-Adjuster-Kit-p/oil-pressure-adj-kit.htm
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Great idea Pops, I'll remember that when I get it running.
On the 1/2VW, the oil galleys to the back two rods, bearings and heads, lifters are plugged, so the pump is oiling only half of the engine. Even if the CAM bearing is a bit oversized, Oil pressure should not be a problem. IMHO!
![IMG_3319[1].JPG](https://cloud-data.nyc3.cdn.digitaloceanspaces.com/homebuiltairplanes/data/attachments/74/74551-af1fbab4d5a99eb7b9215ad139d5b0e4.jpg)
![IMG_3318[1].JPG](https://cloud-data.nyc3.cdn.digitaloceanspaces.com/homebuiltairplanes/data/attachments/74/74552-c4e9b63e45d03278b6d456e8c94771a3.jpg)
As you can see from the pics, Things are moving along. Engine still tight with new cylinders and pistons, but a little oil in the cyl. has loosened them up. Still more to do, but moving along.
Thanks to all who contributed comments, advise, suggestions, encouragements, etc. I feel a whole lot better about the engine.
Johnc (Tuneturkey)
oldcrow
Well-Known Member
For all of those who are building a 1/2 of full VW motors. Remember this, ALL of the parts are made in China now (except for some of the SCAT parts) so tolerances are not always spot on. I have had to use up to 3 different boxes of crank bearings and cam bearings (not as often with the cam bearings ) to achieve a nice fit. A good mic goes a long way.
For sealing the case halves and jugs to block, I have always used the light grey Permatex, but you can use the Gasgacinch gasket maker that VW shops sell. If you do use the Permatex on the case halves be very careful on how much you use. The case halves are so tight to begin with that extra sealant can squish out into the engine cavity and eventually clog an oil passage. Never use any RTV or silicone base sealers. They are not oil PROOF, and really do not belong anywhere on a VW engine. If you need to make a gasket use the black Permatex. It is twice as thick as the grey. Permatex does not get hard or break down over time. And no I do not work for the company, I just know that it works well.
For sealing the case halves and jugs to block, I have always used the light grey Permatex, but you can use the Gasgacinch gasket maker that VW shops sell. If you do use the Permatex on the case halves be very careful on how much you use. The case halves are so tight to begin with that extra sealant can squish out into the engine cavity and eventually clog an oil passage. Never use any RTV or silicone base sealers. They are not oil PROOF, and really do not belong anywhere on a VW engine. If you need to make a gasket use the black Permatex. It is twice as thick as the grey. Permatex does not get hard or break down over time. And no I do not work for the company, I just know that it works well.
do you use plastic-gauge? what are the "not nice fit" numbers for the bearings you reject?....How do those numbers compare with the specification numbers?
oldcrow
Well-Known Member
ok then. just to clarify for those who want to know all the details.
measure your crank journals, rod journals, and cam. with out the cam, crank, or rods installed bolt the case halves together with the bearings installed. Torque the case to specs. (16ft on the outer bolts and 26ft on the inner larger bolts) and i am not going to show you the torque sequence.
now measure your bearings. the difference between the crank journals and the bearing (as well as cam) should fall between .0025 inch and .0030 inch.
for your connecting rods use plastigauge and you should still fall under the same tolerances.
if anyone knows if my measurements are wrong chime in and correct me. it has been a few years since my last build.
measure your crank journals, rod journals, and cam. with out the cam, crank, or rods installed bolt the case halves together with the bearings installed. Torque the case to specs. (16ft on the outer bolts and 26ft on the inner larger bolts) and i am not going to show you the torque sequence.
now measure your bearings. the difference between the crank journals and the bearing (as well as cam) should fall between .0025 inch and .0030 inch.
for your connecting rods use plastigauge and you should still fall under the same tolerances.
if anyone knows if my measurements are wrong chime in and correct me. it has been a few years since my last build.
I can see why you reject them...you are looking for .0005 total tolerance for the bearing/crank. For example my Lycoming has between .0025 to .0055 clearance with .006 service limit
GeorgeG
Member
You can use plastigage on the cam, also. And for gear backlash and other things like that.
oldcrow
Well-Known Member
i dont know the size of lycomings crank but there is a rule of thumb that goes something like .001 per diameter inch or something like that i dont really recall
