# Bob Hoover's HVX VW Engine Mods.

Discussion in 'Volkswagen' started by Pops, Mar 23, 2019.

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1. Mar 23, 2019

### Pops

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I'm just starting to do Bob Hoover's HVX engine mods for a 1973 VW Type 1 case. The case has been machined for 92 mm pistons and cylinders, welded behind #3 cylinder, welding sometimes tends to warp the case and good idea to have it checked and if warped have the main bearing saddles line bored. I had the case checked at a VW Type 1 only machine shop. Everything OK. Also cleared for a stroker crank if I wanted to make it a 2180 cc engine. Decided to use the stock 69mm crank for 1835 cc engine. I had great success in the HVX mod in the 1835 cc engine in the SSSC aircraft. With the increase oil flow to the rocker arms and heads I had no heat problems in a WOT climb as long as I wanted on a 100 deg OAT day. To get a better understanding of the Mods read all of this.
https://bobhooversblog.blogspot.com/2007/05/hvx-mods.html

The only down side that I have found is with the increase oil flow to the heads you will have a slightly lower oil pressure. But that is easy to take care of by going to the larger capacity oil pumps or what I did. The stock oil pump cover uses a .004 paper gasket, I made a new gasket of .002 gasket material from NAPA and raised the oil pressure about 8 to 10 pounds at cruise rpm of 2650/2700 rpm, went from 32 lbs to 42 pounds.

I always drill out the oil passages soft plugs and tap for plugs. Only way to make sure the passages are clean from an machine shaving with the case was made,etc. EMPI makes a kit of all the plugs you will need for $10. If used for an aircraft engine the soft plug just right of the full flow inlet elbow on the pulley end of the case will need to be drilled out and tapped and plugged. http://www.greatplainsas.com/service1.html The plug has a .040 step made into it to act to act as an orifice that supplies oil to the #4 main bearing. When using a prop hub the load on the bearing is much higher than the auto alternator belt and the bearing needs more oil. One of the things that Scott at Humble Engines and Great Planes do to the cases they sell. Next will be taping threads for the plugs, and doing the mods on the lifters and rocker arms and shafts. After that I need to get it as clean as possible, install the plugs with Lock-tite and paint a light coat of flat black paint on the outside of the case to stop any corosion. No paint on surface that get bolted together. #### Attached Files: • ###### DSCF0001.JPG File size: 323.5 KB Views: 47 • ###### DSCF0002.JPG File size: 311.3 KB Views: 48 • ###### DSCF0003.JPG File size: 338.2 KB Views: 47 • ###### DSCF0005.JPG File size: 299.5 KB Views: 44 • ###### DSCF0006.JPG File size: 313.3 KB Views: 47 • ###### DSCF0008.JPG File size: 313.4 KB Views: 47 • ###### DSCF0011.JPG File size: 322.9 KB Views: 48 • ###### DSCF0016.JPG File size: 307.3 KB Views: 46 • ###### DSCF0020.JPG File size: 313 KB Views: 47 Last edited: Mar 23, 2019 wsimpso1, delta, fly2kads and 4 others like this. 2. Mar 23, 2019 ### Vigilant1 ### Vigilant1 #### Well-Known MemberLifetime Supporter Joined: Jan 24, 2011 Messages: 4,053 Likes Received: 1,796 Location: US Pops, Thanks. On the spark plugs--do you plan to use a steel insert in the holes, or just tighten them into the magnesium case? And I hadn't heard of using Loctite on the plug threads (blue stuff?). I've seen recommendations for the normal anti-gall thread compound. Oil filter or no? And will this be a shrink-fit prop hub or the Force One? Another VW airplane engine--how many is this for you? 3. Mar 24, 2019 ### Pops ### Pops #### Well-Known Member Joined: Jan 1, 2013 Messages: 7,131 Likes Received: 6,022 Location: USA. I take my VW heads to a local very good machine shop and have them install steel inserts in the spark plug holes. They are made with a shoulder on the top where there is a hole and a small steel pin in used to lock the insert from ever turning. Always use a anti-gall thread compound on the spark plug threads. I used to use oil filters, but even with the high oil pressure adjusted to about 56 pounds, I had a oil filter split at the top ring. I was still on the ground when it happen. So I don't use a filter anymore, just change oil at 25 hrs and check and record the valve lash. A Great Plains shrunk-fit prop hub is OK on a stock 69 mm crank. GP's says 1914 cc is the limit. This 1835 VW engine will be going in my VW Pipe Buggy. I have parts to build 3 more VW engines and when I finish this engine I need to finish the Fly-wheel drive Aero-VW engine. Not sure if it's going to be a 1835 or a 2180 cc engine. Leaning towards the 2180. Either way, it will have single port heads. Have the heads ready. How many aero-VW engines ? I have built 4 in the past for me, and about 6 or 7 for other people in the past, can't remember for sure, I have slept since then One VW engine on a Tiny-Two flew from the east to the west coast and back. Have no idea how many VW engines for Bugs. I had a side business building stock and hot-rod VW engines for people and bought and sold VW Bugs for several years. In the hundreds for engines. Also have owned hundreds of VW's Bugs. Had one building just for VW engine building shop. Been building VW engines since 1970, getting hard to remember past yesterday Also worked for VW of America for many years. Last edited: Mar 24, 2019 4. Mar 24, 2019 ### Vigilant1 ### Vigilant1 #### Well-Known MemberLifetime Supporter Joined: Jan 24, 2011 Messages: 4,053 Likes Received: 1,796 Location: US Pops, thanks for the link to Bob Hoover's old blog with the info on his HVX mods. It had been awhile since I'd read them. Some great thinking on his part and clever modifications to get more oil to the heads. He claims 8x more oil flow to the heads, better lubrication (esp to the right hand side, as viewed from the flywheel), and even noticeably better cooling to the heads (from the greater flow of oil). It doesn't look like high-precision machining, but still the channels do need to be cut in the right spots and to the right depth. What's your technique for removing the metal in the right places? This can't be as simple as a using a Dremel tool or die grinder freehand and an angle grinder strapped down to the bench. Once everything is set up, it would be short work to do the parts for a bunch of engines. It seems like something Great Planes or Hummel could sell as a ready-to-install kit. Last edited: Mar 24, 2019 5. Mar 24, 2019 ### Vigilant1 ### Vigilant1 #### Well-Known MemberLifetime Supporter Joined: Jan 24, 2011 Messages: 4,053 Likes Received: 1,796 Location: US Ahh,I should have searched a bit before bothering you. Here Bob Hoover shows/discusses some of the techniques for doing the channelling and drilling. I suspect he's got more tips sprinkled throughout his blog pages, the search function works pretty well there (if I'd only used it! ) I don't know if the Aerovee/Great Plains "hybrid" in my Sonex has had the HVX mods done, I'll have to look at the rocker arms and a rocker shaft the next time I have a chance. The builder of the plane and the engine had a lot of experience with building racing VWs, and he also had the (common) problem with the oil runner to the #4 bearing (causing him to have the case line bored and giving him the opportunity to install the Force One bearing/hub). Last edited: Mar 24, 2019 6. Mar 24, 2019 ### Pops ### Pops #### Well-Known Member Joined: Jan 1, 2013 Messages: 7,131 Likes Received: 6,022 Location: USA. No high-precision machining needed to enlarge the oil grooves that are under the cam bearing shells. Not done on the flywheel end of the cam bearing saddle. These square oil grooves are about 3/16" square. I just take a 1/4" dia grinding stone that came with my Dremel tool and rounded the sides but not any deeper. B. Hoover doesn't say how he did it. Just how he made the grooves in the outside of the lifters and the rocker arms and shafts. Got the case threaded for the case oil passage plugs. Be careful not to tap to deep where the threaded plug will go deep enough to plug or restrict oil passages that branch off to the sides in different places. Do not use longer threaded plugs, the length of the plugs in the EMPI kit are just right. Picture of the oil passage plug for #4 bearing and you can see the .040 step in the plug for an orifice. Wouldn't take much metal shaving left in the oil passages or other junk to stop the small oil flow to the #4 bearing. I will be using the brushes and tools from my gun cleaning kit to clean all the oil passages. Even if you have a new case, the oil passages need to checked for machining metal. Also picture of the stock German 69 mm crank I will be using. I'll have to install the #3 bearing and then the cam gear and dist drive gear on the nose of the crank. An overnight stay in the freezer for the crank and heating the gears in oil to 450 degrees makes it easy. #### Attached Files: • ###### DSCF0001.JPG File size: 315.7 KB Views: 40 • ###### DSCF0004.JPG File size: 329.1 KB Views: 41 • ###### DSCF0005.JPG File size: 314.4 KB Views: 40 • ###### DSCF0006.JPG File size: 316 KB Views: 46 dmar836, don january and Vigilant1 like this. 7. Mar 25, 2019 ### Joe Boyle ### Joe Boyle #### New Member Joined: Mar 23, 2019 Messages: 3 Likes Received: 0 Pops, Please give me a call at 301-797-1875 or e-mail me at joeboyle1@myactv.net about the 8' Brake, the roll and the pan and box brake. I'm new to the site and am not sure if I've been able to reach you on several other attempts I've made on this site. 8. Mar 25, 2019 ### Pops ### Pops #### Well-Known Member Joined: Jan 1, 2013 Messages: 7,131 Likes Received: 6,022 Location: USA. don january likes this. 9. Mar 25, 2019 ### Pops ### Pops #### Well-Known Member Joined: Jan 1, 2013 Messages: 7,131 Likes Received: 6,022 Location: USA. OK. Dan 10. Mar 26, 2019 ### Pops ### Pops #### Well-Known Member Joined: Jan 1, 2013 Messages: 7,131 Likes Received: 6,022 Location: USA. Got the oil grooves in the lifters finished. Took maybe 1/2 hour to do all 8 lifters. Used a 1.5" X 1/16" thick cut-off wheel . I buy the 4" dia cut-off wheels in 1/32" and 1/16" thickness at the local hardware store and drill a 1/16" dia hole and draw a circle with a compass for a 1.5 dia wheel and cut out with aviation snips. Far better than anything else I have used in the dremel. #### Attached Files: • ###### DSCF0008.JPG File size: 296.3 KB Views: 42 Vigilant1 and don january like this. 11. Mar 26, 2019 ### Pops ### Pops #### Well-Known Member Joined: Jan 1, 2013 Messages: 7,131 Likes Received: 6,022 Location: USA. Affordable Aviation. People keep talking about affordable Aviation. Can't get much cheaper that scratch building a VW powered V-Max, Fisher Super Koala, etc, etc. And scratch building a VW engine from parts from GP's and Scott at Humble. http://www.greatplainsas.com/chooseaircrft.html https://fisherflying.com/aircraft/ Seems like not many people interested if there is any work and learning involved . I can't , never did anything. I still remember my 8 grade teacher making everyone in the class get up in front of the class and reciting the poem " It can't be done". One of many. Last edited: Mar 27, 2019 dmar836 and sotaro like this. 12. Mar 27, 2019 ### Pops ### Pops #### Well-Known Member Joined: Jan 1, 2013 Messages: 7,131 Likes Received: 6,022 Location: USA. I had this engine case checked out by the local VW engine only machine shop that I have been using since 1970. Yesterday I saw something that didn't look right. At the top of the bore in the case where the lifter for the intake valve for #1 there was a very, very small line that looked out of place. With a strong light and a magnifying glass, there was a small crack starting at the top and starting to go down in the bore. The shop must of missed it, I can see why. Not going to use the case. It would be OK for a 1/2 VW if someone wanted to build one. Bored for 92 pistons and cylinders, and cleared for a stroker crank. So, I dug out another case that I have that is good and did all the drilling and thread tapping and enlarging the oil passages on it the rest of the day. Next thing on the HVX mods will be the rocker arms and the rocker arm shafts. Making the grove inside the rocker arm bushing is the hardest part of doing the Mods. Also when doing the mods to the shafts, it makes the shaft end locked to a certain end of the heads. 13. Mar 27, 2019 ### harrisonaero ### harrisonaero #### Well-Known Member Joined: Oct 31, 2009 Messages: 549 Likes Received: 279 Location: Coeur d'Alene, ID I'm not a big auto engine conversion fan but when I was more interested in them a couple decades ago I was communicating with Mr. Hoover on RAH and did a fair amount of research. Conclusions? Piston speed is the #1 indicator of aircraft engine reliability and a VW with a redrive to reduce cyclic bending load to the crank and keep thrust up by the square of the diameter is feasible compared to piston speeds of a Lycoming or Rotax 912. According to Mr. Hoover the weak point for higher hp is the VW case. With modern HSM a new strengthened case with HVX and other cooling mods plus the incorporation of redrive mounting ala Rotax is feasible. With a redrive and an excellent oil cooler you could have a simple engine that would swing a big efficient prop for a relatively low cost. 14. Mar 27, 2019 ### samyguy ### samyguy #### Well-Known Member Joined: Sep 20, 2011 Messages: 102 Likes Received: 17 Location: Lincoln Nebr Keep the details and photo's coming Pop's thanks 15. Mar 27, 2019 ### Vigilant1 ### Vigilant1 #### Well-Known MemberLifetime Supporter Joined: Jan 24, 2011 Messages: 4,053 Likes Received: 1,796 Location: US I'm not quite following you with regard to the purpose of the PSRU and RPMs on a VW. A large displacement VW engine will have a stroke of 82MM, while a Continental O-200 has a stroke of 98.5 mm, which is about 17% longer. That means that our VW engine at 3200 RPM (where we typically run them) has a piston speed less than an O-200 at 2700 RPM. Are you arguing for turning the VW at even slower RPMs using the redrive? If so, we won't see HPs up to the heat rejection capability of the head (e.g. approx 76 HP for a 2180cc engine). I suppose we could do it with a higher compression ratio, but that's taking us in the opposite direction WRT bearing pressures/reliability. The primary failure induced by prop loads/crank bending is crankshaft failure. With a proper crank and front bearing on the bigger engines (ala Revaster's built-in front bearing or the GPAS Force One prop hub and bearing) crankshaft failures on VW-derived aircraft engines are very rare now. So, I thin the only advantage of a PSRU would be the ability to turn a longer prop at the present VW engine RPMs (approx 3200-3600). Well, the magnesium cases do wear out eventually (bearing saddles, cracks). That could be a very long time down the road for most folks. Before that, they have typically gone through several heads, which I would characterize as the weak point for higher HP VW engines. Luckily, they are a lot easier and cheaper to repair/replace than a case. And it is far less of an issue if temps are kept reasonable and the HP demands are not continuously at the bleeding edge of the engine's capability. sotaro and Pops like this. 16. Mar 27, 2019 ### Pops ### Pops #### Well-Known Member Joined: Jan 1, 2013 Messages: 7,131 Likes Received: 6,022 Location: USA. Weight is the enemy and using a redrive along with the necessary starter( when using a redrive), battery, alternator, wiring, etc, adds a huge percentage of weight. So much so, you are in the small Cont range. Its hard to beat a non-electric, straight drive, 1835, 60 hp, VW engine for power, reliability, light weight, fuel burn, cost. Does a good job of swinging a 60"x26" prop in a draggy airframe , 480 lb EW and my 230 lbs + 10 gal fuel. Last edited: Mar 27, 2019 dmar836, ArcticDave and Vigilant1 like this. 17. Mar 27, 2019 ### Vigilant1 ### Vigilant1 #### Well-Known MemberLifetime Supporter Joined: Jan 24, 2011 Messages: 4,053 Likes Received: 1,796 Location: US Your post the other day prompted me to look at the Great Plains flywheel drive kits. I hadn't noticed before, but they sell these kits for 2180cc and 2276cc engines. The prices don't appear to include a different bearing and hub for these stroker-crank engines. I recall that Steve Bennett was pretty adamant about the need for the special crank and the Force One bearing on the "pulley drive" stroker engines. In your opinion, does the beefier bearing and the lack of the Woodruff key slot on the flywheel side make it okay to go that high, or would you stop at 1835cc (60 HP)? 18. Mar 27, 2019 ### Pops ### Pops #### Well-Known Member Joined: Jan 1, 2013 Messages: 7,131 Likes Received: 6,022 Location: USA. Steve told me that there was no problems with the #1 main bearing and crank on the flywheel drive engines up and including the 2276 cc engines. The "Force One" prop hub and large Force One bearing is used on the pulley end drive for the 2180cc and up to 2276 cc engines with a stroker crank. When using the stock 69mm throw crankshaft for up to 1915 cc, the taper or sunk fit prop hub is used, ( Be sure to drill out the orifice restriction that supplies oil to the #4 bearing when using the pulley end no matter what prop hub you are using on the pulley end). I ask Steve if I should use the Force One on the 1835 cc engine. He said that there was no need. The problem with the flywheel drive engine is no one makes a mag drive for the pulley end. So if you want an flywheel drive non-electic engine about the only choice you have is to use the auto distributor and a windmill generator. I have most of the parts made for putting a mag on the pulley end, but just haven't had time to get back on the project with trying to finish the JMR. Will have to use the universal replacement case that has the threaded bosses on each side of the oil pump to mount lower part of the housing of the mag mount. These bosses are used to mount the rear engine mount in the buses. 19. Mar 29, 2019 ### Pops ### Pops #### Well-Known Member Joined: Jan 1, 2013 Messages: 7,131 Likes Received: 6,022 Location: USA. Took some VW rods from the part box and weighted them. Look at the difference of weights. This is the reason you need a matched set of rods for long engine life and smooth running with more power. Two rods weighed --580 grams, Three rods weighed --585 grams, One rod weighed -- 590 grams, Two rods weighed --600 grams, One rod weighed-- 610 grams. At the local VW only VW parts/ machine shop, they will swap you a set of rods that have a match total weight to within one gram, new wrist pins bushing installed, equal weight on each rod end and exact distance from center of the large and small hole of each rod. The last set I bought was$15 each and a set of old rods.
Can't beat that.

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20. Mar 29, 2019

### Alan_VA

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(New guy here, trying to sort out the gems from the dross.) How closely does your shop balance the rods? IIRC, Bob Hoover was pretty insistent on that as well.

Alan