K&B 7.5 titanium rod

Discussion in 'Motors Forum' started by JoePavelich, Mar 5, 2019.

intlwaters.com

Help Support intlwaters.com:

  1. Mar 5, 2019 #1

    JoePavelich

    JoePavelich

    JoePavelich

    Member

    Joined:
    Feb 18, 2019
    Messages:
    11
    Location:
    Farmington Hills,Michigan
    Anyone know of the availability of a titanium rod for a K&B 7.5 ?
     
  2. Mar 5, 2019 #2

    brad nichols

    brad nichols

    brad nichols

    Well-Known Member

    Joined:
    May 10, 2010
    Messages:
    2,318
    Terry Keelly may of made some but if you can find a RPM rod they are good. What are you building as you are going to spend $$ on all the parts ?

    Brad
     
  3. Mar 5, 2019 #3

    JoePavelich

    JoePavelich

    JoePavelich

    Member

    Joined:
    Feb 18, 2019
    Messages:
    11
    Location:
    Farmington Hills,Michigan
     I have been out of boating since the early seventies. When I raced a White heat 4-60 with a 65 Rossi , a Don Pinkert rigger with a Super Tigre 65 and my last boat a Crapshooter with a Super Tigre 65. I picked up this new K&B 7.5 relatively inexpensive and am going to try a Phil Thomas Stealth 45. A new CMB , Novarossi or Double Ace would be about $400 more than my K&B. I am also building Blazer Lauterbach and am trying to keep the budget down. 
     
  4. Mar 6, 2019 #4

    brad nichols

    brad nichols

    brad nichols

    Well-Known Member

    Joined:
    May 10, 2010
    Messages:
    2,318
    Run it until it goes KaBoom. Then you can hopefully get a newer one.

    Brad
     
  5. Mar 6, 2019 #5

    Mark Anderson

    Mark Anderson

    Mark Anderson

    Well-Known Member

    Joined:
    Nov 22, 2002
    Messages:
    465
    Location:
    Washington
    The K&B rods were ok. No need to replace unless it has one of the round unbushed rods. They were hard anodized and had no bronze bushing in the big end. Not sure if they were ever put in the 7.5 inboards or not. 
     
  6. Mar 6, 2019 #6

    Jim Allen

    Jim Allen

    Jim Allen

    Well-Known Member

    Joined:
    Jun 7, 2005
    Messages:
    1,552
    Location:
    Graham, NC
    It is very difficult to use any Titanium alloy as a connecting rod material in a miniature two cycle engine! If your interested, I'll explain why from actual experience.

    Jim Allen
     
  7. Mar 12, 2019 #7

    Alan Elzer

    Alan Elzer

    Alan Elzer

    Well-Known Member

    Joined:
    May 21, 2006
    Messages:
    943
    Location:
    Boonville, IN.
    I have one if still interested. It been In a box of parts for several yrs. Has some oxidation in bushings but scotch brite should clean it just fine. Was never used in motor.

    Sent from my SM-N920V using Tapatalk
     
  8. Nov 3, 2019 #8

    MikeReed

    MikeReed

    MikeReed

    Member

    Joined:
    Oct 3, 2014
    Messages:
    11
    Location:
    Copperas Cove, TX
    Hello Jim, I'm interested.

    What about 7068 Aluminum? Its supposed to be just as strong as Titanium without the BS of machining Titanium (or its thermal properties).

    EDIT: I found this on Wikipedia (yeah I know for whatever its worth but....) "Primarily developed for ordnance applications, alloy 7068 is now being used or considered for markets like the aerospace and automotive industries (valve body and connecting rod applications)"
    TENNALUM-7068-HIGH-STRENGTH-ALUMINUM-ALLOY-700x434.jpg
    https://precisionarmament.com/tennalum-7068-aluminum-alloy/

    Thanks,
    Mike
     
    Last edited: Nov 3, 2019
  9. Nov 5, 2019 #9

    Brad Christy

    Brad Christy

    Brad Christy

    Well-Known Member

    Joined:
    Jun 25, 2002
    Messages:
    1,039
    Joe,

    I'll have to check when I get back home, but I'm pretty sure I have a 7075 rod for a KB 7.5. It COULD be Ti, but I'm thinking its 7075.

    Jim,

    While I won't question your experience, I will tell you that I've been running Ti rods in my engines for years. The key to is to make sure there is no frictional contact between the Ti and any steel parts. A properly relieved bottom lobe will allow for contact between the bushing and the crank face, but prevent the Ti from making contact.

    Mike,

    Ti is not that difficult to machine. Slow spindle speeds, heavy feed rates and keep everything cool. I've been using the same solid carbide roughing end mill to make connecting rods ( and other parts) for more than a decade.

    For what it's worth, the 7068 is almost unobtainium. I had an RFQ for some 7068 parts a while back, and ended up finding some after some considerable searching. I eventually found it on eBay, tracked down the seller and bought it direct. I could only buy the drops they had left over from purchases made by military contract MFRs, and only if those drops weren't potentially sought by those MFRs (these drops were what was on eBay). I still have most of what I bought, and I hold it fairly close to the chest.

    Thanks. Brad.
    Titan Racing Components
    BlackJack Hydros
    Model Machine and Precision LLC
     
  10. Nov 9, 2019 #10

    Jim Allen

    Jim Allen

    Jim Allen

    Well-Known Member

    Joined:
    Jun 7, 2005
    Messages:
    1,552
    Location:
    Graham, NC
    6AL4 V Titanium does work in smaller size engines. Since Titanium alloys are not bearing materials it will be necessary to provide a suitable bearing surface in the upper & bottom ends. Titanium alloys also have very poor thermal conductivity, therefore any heat developed in the bushed ends of the rod remains there causing the rod to close down on its crank or wrist pin. Henry Nelson & I were able to get the bushed bottom ends of Titanium rods to survive at RPM's beyond 24,000 by running a bottom end clearance of more than .0065". Titanium connecting rods that used any type of roller assembly in the bottom end also did not work with drawn cup bearings or machined roller bearings because it is impossible to hold whatever type of hardened bushing that can be used without distorting the bushing. A great deal of time went into determining that the best material for a connecting rod in a larger size engine is hardened & tempered STEEL!

    Jim Allen
     

    Attached Files:

    Last edited: Nov 10, 2019
  11. Nov 10, 2019 #11

    Rudy Formanek

    Rudy Formanek

    Rudy Formanek

    Well-Known Member

    Joined:
    Dec 6, 2003
    Messages:
    577
    Jim, did you ever use loose needles in your steel con rods??
     
  12. Nov 11, 2019 #12

    MikeReed

    MikeReed

    MikeReed

    Member

    Joined:
    Oct 3, 2014
    Messages:
    11
    Location:
    Copperas Cove, TX
    Jim Thanks for the info. I do have one question though. In the above you talked about holding roller bearing assemblies but then said it couldn't be done without distorting the bushing. Did you mean without distorting the bearing? Is the distortion a result of running the engine, or when fitting it to the rod.

    I'm interested because I've been playing around with modifying glow engines with hardened dowel pins and caged roller bearings in the rods. My intention is to run them on Ethanol (E85 pump gas primarily or VP fuels canned E85 & E90 but also home made E85, E90 and straight E100) and RedLine Alcohol oil.

    The pics are of a little Enya .35(high compression head) I modified just to see if I could do the mods. Yes.... I forgot to remove the glow and put in the spark plug for the picture. The other two pics are of a K&B 1.00 I modified, it'll be on ignition as well but I'm also converting it to reed valve induction. I still need cut the hole for the reed cage into the new backplate and also make heat spacer of some sort. I have some Delrin and as its Ethanol I think the heat will be low enough for it. The last picture is a HB .61 PDP crankshaft I modified with a long pressed in pin for a guy so he could run an accessory backplate that drives a fan for a helicopter application.

    One thing I have not found any definitive answers on is the press fit clearance amount. On the Enya crank I used .0015 undersize before pressing in the 3mm dowel pin. On the 1.00 I pressed in a 6mm pin at .0012" undersize because that was the only reamer I had. I also try for .0012" for the caged bearings in the rods. I'm worried its not enough though but I don't want to crack anything apart either. So when I press them in I've been using Loctite 620 and heat curing it at 356deg for an hr.

    Mike
     

    Attached Files:

  13. Nov 11, 2019 #13

    MikeReed

    MikeReed

    MikeReed

    Member

    Joined:
    Oct 3, 2014
    Messages:
    11
    Location:
    Copperas Cove, TX
    Brad,
    Thanks for the info. I bought a few pieces Ti and was playing around with it. I'd made some aluminum fuel tank assemblies and thought it would be neat to try one in Ti since I had the pieces. I'm still learning this stuff. I found best cuts at about 700rpm at .008"doc with those generic insert tools sets you get off Amazon. I think I speed it up to about 1000rpm for a shallow finish pass and I thought it looked pretty nice. I was also surprised at how well it drilled with standard HSS drills but when I went to tap a hole, the tap broke about 4 turns in without any warning or feel. So I boxed it all up to try again some other time.

    About the 7068, I've seen those eBay auctions for cutoffs and have been tempted to get a couple. Do you think its strong enough to run without bronze bushings? Maybe for sport applications <18,000rpm?

    Mike
     

    Attached Files:

    Last edited: Nov 11, 2019
  14. Nov 11, 2019 #14

    Brad Christy

    Brad Christy

    Brad Christy

    Well-Known Member

    Joined:
    Jun 25, 2002
    Messages:
    1,039
    Mike,

    7068 is plenty strong enough, but it won't work without bearing material between the steel and the aluminum. Use 544 phosphor bronze for bushings and you'll be fine.

    For the Ti, I use all carbide tooling, including drills, except for taps. With the roughing end mill, I use it full depth whenever possible, at about 500 RPM and a .0025" chip-per-flute standard feed. For tapping, you have to do by hand (my experience), and you have to use a pretty heavy cutting fluid (I use MolyDee) with frequent in-and-outs, making short 1/2 to one turn cuts at a time. It's nasty work, but sometimes the work calls for it. One time, I had to put 16 1-72 tapped holes through a .125" thick section in a part. Took me an entire day. Ick.....

    Hope this helps. Brad.
    Titan Racing Components
    BlackJack Hydros
    Model Machine and Precision LLC
     
  15. Nov 11, 2019 #15

    Brad Christy

    Brad Christy

    Brad Christy

    Well-Known Member

    Joined:
    Jun 25, 2002
    Messages:
    1,039
    Jim,

    Again, not to question your experience, but...

    I've been running Ti rods in my engines for a long time. I've got two MAC45s with Ti roller rods that run like swiss tops. These have uncaged full compliment roller bearings. I know of a handful of OPS 90s with equivalent rods (Ti with rollers) in them that have been running for years without failure. Countless MAC67s and 84s, same thing. I had far more problems out of Ti rods with 544 bushings in Picco 45s and 67/80s than I ever did anything with rollers. I eventually gave up on Picco Ti rods, and have made them from 7075 ever since.

    As I said, proper relieving of the Ti away from any rotating steel parts solved any problems. I never had to relieve the upper end of any rods. There just never seemed to be any pressure or enough motion to cause any issues.

    Thanks. Brad.
    Titan Racing Components
    BlackJack Hydros
    Model Machine and Precision LLC
     
  16. Nov 11, 2019 #16

    Brad Christy

    Brad Christy

    Brad Christy

    Well-Known Member

    Joined:
    Jun 25, 2002
    Messages:
    1,039
    Mike,

    One suggestion......

    If your going to make Ti rods for bushings, make your pre-bushing holes with a series of end mill plunges that leave scallops, as if done with a broach, that will spline into the bushing material. If you're going to make Al rods with bushings, make the bushings with these scallops on the OD of the bushings so that they spline into the rod material. If you're going to make Ti rods with a roller sleeve, make the sleeve with these scallops on the OD, again, so that the sleeve splines into the rod material. These seemingly overkill efforts will save you a lot of heartache down the road.

    Hope this helps. Brad.
    Titan Racing Components
    BlackJack Hydros
    Model Machine and Precision LLC
     
  17. Nov 12, 2019 #17

    Jim Allen

    Jim Allen

    Jim Allen

    Well-Known Member

    Joined:
    Jun 7, 2005
    Messages:
    1,552
    Location:
    Graham, NC
    The answer to this is definitely yes Rudy. The size of the engine in question will make a difference as to what works & what will not work. No one has ever calculated or attempted to calculate what effect the displacement, coupled with the engine's RPM has on this fact! However, after thousand of hours of testing, what we found is that loose needles can work when the RPM's are below 24,000 in .45 to 1.00 cu in engines. The RPM limits are much higher in .21 to .45 cu in engines, even when Titanium rods were used. What happens in any loose, unguided needle assembly is the helix angle of the needles in relation to the axis of rotation increases with the rotational speed of the assembly. Look in any needle bearing catalogue & it can be easily seen that guided needles have a much higher rotational RPM than unguided needles. However, loose full complement needles can carry a larger load.

    Consider how needles are guided in any common "A" or "W" type cage needle assembly. The needles remain in the cage assembly only because they are guided above & below their center line. This type of guidance prevents positive alignment of the rollers to their axis of rotation. A "machined cage" guides the needles on their center line from end to end, preventing the development of any helix angle. This feature allows a "machined cage" needle assembly to attain a very high rotational speed. The highest tested speed in the .90 cu in engine is 37,000 RPM. A latter development of two needles mounted in single machined cage window greatly increased the assemblies load carrying ability & its wear resistance capabilities without any loss of RPM.

    Final total radial clearance numbers for a machined needle caged assembly was .0002" to .0003". In the posted photo of the rear of the engine, the two needle, machined cage assembly, can be seen. It can run indefinitely on 8% oil. Also notice that there are 16, .0625" needles on a .3281" OD crank pin. In my 27 cc gas engines there are 13, .0787" needles on a .3937" crank pin. The 4 additional needles over the stock needle assembly increases the load carrying & wear resistance of the assembly. The radial clearance for a machined caged assembly in my gas engine is .0003" to .0005".

    Jim Allen
     

    Attached Files:

    Last edited: Nov 15, 2019 at 7:14 AM
  18. Nov 13, 2019 #18

    Jim Allen

    Jim Allen

    Jim Allen

    Well-Known Member

    Joined:
    Jun 7, 2005
    Messages:
    1,552
    Location:
    Graham, NC
    "One thing I have not found any definitive answers on is the press fit clearance amount. On the Enya crank I used .0015 undersize before pressing in the 3mm dowel pin. On the 1.00 I pressed in a 6mm pin at .0012" undersize because that was the only reamer I had. I also try for .0012" for the caged bearings in the rods. I'm worried its not enough though but I don't want to crack anything apart either. So when I press them in I've been using Loctite 620 and heat curing it at 356deg for an hr."

    Mike,

    The press fit amount will be determined by the hardness of the alloys involved & the finish on both pieces. As an example, the crank pin in my .90 cu in engine is pressed into the crankshaft with .0013" to .0015" press fit. The crankshaft is AISI-S7 which is fully hardened & tempered with the hole ground to a very smooth finish. The entrance of the hole is radiused & highly polished. A fixture & a hydraulic press will be required to press the pin in. The crank pin is a fully hardened 52100 or M-2 steel piece cut from a pre-hardened & precision ground blank. It is also radiused & highly polished on its leading edge. Either alloy works for a crank pin, but the M-2 steel has a higher wear resistance when used for needles or crank pins. I use a similar setup in my gas engines three piece crankshaft with the same alloys, same design features & the same resultant very high reliability because the engine operates in the 23,000 RPM range.

    Jim Allen
     

    Attached Files:

  19. Nov 13, 2019 #19

    Jim Allen

    Jim Allen

    Jim Allen

    Well-Known Member

    Joined:
    Jun 7, 2005
    Messages:
    1,552
    Location:
    Graham, NC
    Mike,

    You asked the following question: I do have one question though. In the above you talked about holding roller bearing assemblies but then said it couldn't be done without distorting the bushing. Did you mean without distorting the bearing? Is the distortion a result of running the engine, or when fitting it to the rod.

    The fact that a connecting rod does not have the same thickness of metal around the bushing area has always presented a problem with a press fit. It is necessary to use a .002" press fit in our .45 cu in, 30,000+ RPM speed engines for bushed bottom end assemblies. They have a .004" clearance on the crank pin. Measuring the bushing before & after this process indicates that it is no longer round once it is pressed in. The cutting of splines on a bushing's OD & in the ID of a Titanium connecting rod has been successfully used in many full size helicopter engines. This technique has also been used in .21 cu in size speed engines that used Titanium connecting rods operating in the 40,000+ RPM range. It should be noted that these control line speed engines use .0312" needles mounted in a hardened Beryllium copper retainer. There are three needles in each window.

    We did many experiments with full complement & caged drawn cup needle type bearings. Full complement types had RPM limiting problems because of the helix angle problem & caged types contained fragile plastic cages. None of the caged type drawn cup bearings survived at RPM's beyond 24,000.

    The solution to all of these problems turned out to be a one piece "I" beam type connecting rod which is fully hardened & tempered. Align grinding of the upper & lower holes to each other in two axes after tempering eliminates any distortion or out of roundness problems. Since all the parts, the crankshaft, the crankpin & the connecting rod are made of steel, they all expand at the same rate.

    Jim Allen
     

    Attached Files:

    Last edited: Nov 13, 2019

Share This Page



arrow_white