Lapping conrods on a lathe

Hi,

it`s reg lapping conrod races of an ole Harley.

I`ve got an adjustable external lap with a tapered mandrel chucked in the lathe, dia: 1.6" length ~ 4"
Jims Rod Lapping Set 9674-36, Transfer Case - Amazon Canada
The races to lap have a length of approx .5"

Before I`m messing up a real rod I`m using a dummy of mild steel
I`m pushing the dummy onto the lap, adjust it that there`s still some play, put a few dabs of compound onto the lap (12 and 6 o`clock), shift the dummy back & forth and tighten the lap a bit more. Then I drip some thin oil onto the lap

Speed 160rpm, Silicone compound grit 280 (with oil)

My problem is that the dummy conrod is bellmouthing badly because the compound is building up on the right and left end of the lap. I`ve tried various methods to avoid this but nothing is satisfactory. I loosened the lap to have more play and being able to reach the end of the lap but this doesn`t work for me. Hmmmm.

Anyone can chime in with some wisdom?

Thanks for some comments
Rainer

EDit
I know that profesional wrenches are using honing machines but these shops screwed up my cylinder and heads and the ole fart I am looses patience rapidly. I know that there are good shops but I simply can 't find them and I`m not stingy at all. Sorry for the rant.

IMO, that's one of the problems with loose abrasive compared to honing stones. With the hone, having a long mandrel and a short thing to lap is still an issue. The usual solution is to shorten (grind away) some of the mandrel until it's only slightly longer than the length being honed. The stroke has to overlap the tool a bit. Hard to do with only a .5" length. I don't know if the same technique works with the type of lap you're using, plus once you grind, you can't go back. Finer compound might help, but could take forever.

Loose abrasive lapping is probably not going to work. You might try a lap of a softer metal such as cast iron, brass , or copper. Roll the lap in the abrasive hard to press it in or to "load" the lap. This will help your bell mouth problem. Lapping is very slow how ever. Another trick with identical parts is to stack them and hone as one piece. May not be possible with your parts.

If you make some "dummy" rings of the same size as the conrod bore, then stack them to either side of the rod, you should have them become "sacrificial" pieces to bellmouth rather than the actual rod.

Be certain you have a good way to align the rod and prevent the bore from moving off-axis to the proper geometry. If you can't be sure of maintaining this correctly, I'd put more effort into finding a good shop. It's Germany, for heaven's sake, there has to be someone...

You are using too much abrasive.


Sent from my iPad using Tapatalk

Are you using the entire length of the lapping bar and thinning the compound with enough oil. The reason for using the entire length is not only does it produce a proper pattern for the rollers to wear into but also keeps the lap wear consistent end to end and helps distributes the compound. There are no retention groves in those Jims lapping bars as the laps made Kent Moore shown in the Harley service manuals? Maybe it doesn't matter but that is what I use when doing them. I also think I would prefer to use a horizontal mill with the table dropped down out of the way, seems easier to work the bore without putting any side pressure on it?
Dan

Thanks for your thoughts,

I`ve done some honing before (some mc related some not) and those techniques (shortening etc) do not apply to this lap imho. Except for possible stacking what I favor
The automotive machining shops here are thinning out dramatically and those I contacted bs`d me with ... odd size ... only 2 pcs ... busy ...
Bikeshops I called wanna sell me complete new units only

Too much abrasive ?
Hmmm Thanks for reminding me !
Now that someone else coming to this conclusion: Yeah ,it IS a possibility and I will try some runs with even less compound

The repeated mentioning of "slow process" makes me think again: I am actually surprised how quickly I can take off .0004. It takes me less than 2 x 5 seconds
I did not buy the grit 280 abrasive compound. Someone supplied me 4 spoonful in a facial creme cup. I must ask him wether it was truelly grit 280

Dan, good eye! You`re right the JIMS tool is rather cheap and provides these hacksaw-type cuts only. Well this is what I have but I know that many pro-wrenches used this JIMS tool. It`s definitly not the Kent-Moore quality but it should do its job (saying: It`s my fault)

Sidepressure is another factor. The dummy conrod isn`t balanced of course and so I need to hold it in my hands very short but then I don `t get this feeling for the proper float back and forth..
Hard to explain.

Thanks gents, really appreciated.
I try using less abrasive and more oil
I must make sure wether it is grit 280 compound
When I still cannot develop the skill I`ll stack it up. This should work

Hopefully by sunday I can let you know how I`m going.
rainer

Technique

Have you seen how a Sunnen type hone has a bar to guide the small end of the rod so it stays square, to reduce the bellmouth of the big end.

Without the bar the Conrod wants to spin, so you need to hold against spinning and slide back and forth. With the bar you only need to control the back and forth.

I have this scary view in my head of the lap mounted in a lathe chuck and the rod held by hand. I hope I'm wrong but in this case it will always be bellmouthed due to rocking at reversal. The fact that you can take this much off in this amount of time also points to too much and too rough of abrasive. Finer grits and more lube along with slower strokes will reduce the amount of "rocking" if indeed a non-fixtured operation. Bob

Making progress

Tom, yea I know the Sunnen type that`s why I`m resting the small end of the dummy-rod on the compound of the lathe and simply slide the big end back&forth over the laphead.
Then I used a pair of stack plates and it works pretty good. The rocking motion and therefore the bell mouthing is minimized alot , I`m down to +- .0004. Still too much imho but it is round now and not anymore oval-shaped

Still either stackplate (round, 3" outer dia) got stuck some times so I meassured the laphead (again) and found 2 high spots (+ .0016 ) which I missed earlier. I really cannot explain how I could have miss them ...
I want to use a stone for that matter.
I ordered some #320 compound cause I cannot believe that I have to use so much oil and so lil compound. Just to be safe.
Cause the tigther I adjust the head the less rocking I have

Bob, safe work procedures look different but I don`t know of any other possible way (except for the Sunnen machine). Well it was the advised procedure of the MoCo till 1985 but I need to be on my toes with this type of work reg safety.

Perhaps you have seen this. Article: Some Notes on Refurbishing Narrow Connecting Rods

V twin? It has been about fifty years since I worked for H.D. I am probably stating the obvious but make sure you lap the rods as a pair.

I have been a harley rebuilder for years. When I started out we used adjustable cast iron laps in the lathe. It took some skill to do accurate work and it was very slow. The laps and lapping compounds are still available but aren't used alot because most people spend the money and buy the sunnen equipment because it is easier and faster to do accurate work. Most bellmouth issues and out of round issues are from having the laps too tight and being in too big of hurry. The old engines require main bearing fitting in addition to the rods, the same with the transmission bearings.

I used to go to a lot of engine rebuild shop closedown auctions to buy equiptment in good condition............There wasnt much of that.......especially Sunnen hones worn to the point of scrap metal.......the carbide sizing rods worn like cotton reels.These guys were charging standard trade rate...yet creaming off all the profit with no replacement for worn tooling.Too many hotrods,choppers and tatts.

Thanks all,
after 5 weeks (!) of trying, sweating, cursing and working with dummy conrods I lapped my conrods with this JIMS tool and Clover 320 both within .00013. Round and almost 100% cylindrical.

I lapped them independently not together.
Speed 160, I tried 250rpm but I`ve the impression that the oil I use (Hydraulic oil HLP32) is slung off too quick.So 160 is it.

Anyway I use plenty oil and spreading lightly the compound after each run (maybe 10-15sec), turn it around , oil the lap and fingerdip the compound again. I use a boregauge with a .00005 dial to watch my progress
Very very timeconsuming.
It took me much too long to understand what several members mentioned, for not adjusting the lap too tight.
Ole farts need longer to grasp I suspect
To understand that special floating fit was a steep learning curve. The male rod was torn outta my hands several times (lap too tight, not enough oil, too much grinding compound)

Another concern is trueing the lap. Quite annoying cause I fixed the lap in a collet and centered it with the tailstock. So it was true however after adjusting it altogether maybe a .002 (in many tiny steps each maybe 1/32 turn of the nut) the laphead was out of true again (not the mandrel). I suspect that compound drippes onto the tapered mandrel and after readjusting the laphead the mandrel wears off. The dial prooves it.
So I shaved the laphead with a sheartool again.

I use the full length of the laphead. pull and push the rod quickly from one end of the laphead to the other and remain maybe for 1 second at each`s end

For lapping the male rod I need to use a stackplate, without it bellmouths.
The female rod is a breeze to lap, no stackplate, piece of cake
I`m holding both rods close fisted but not tight. I need to feel when to push it upwards.
Impossible to explain

For lapping the bores absolutely round I need to hold the rod (both 7.44 inches long) at 9:00 o`clock and after a few seconds of lapping, turn the rod from 9:00 to 12 o`clock and continue like before. Don `t ask, but only then it will become 100% round.

One pro-wrench from NC told me this:
Book says .00025 or better. As a practical matter, that can be hard to achieve. Takes some practice, whether lapping or honing.
Let me say, THE most important thing on this job is that the rear rod races be the same size, especially in the "up and down" direction as you can possibly make them. Book says the rear races should be the same size within .0001. Front and rear races should be the same size within .0002.
Book also gives roller clearance of .0004 - .0017. I personally think the low limit here is WAY too low. I shoot for .0008 - .0012, and I feel that a lot of "tight" rod problems are solved using these limits.

I hope that I have the knack out of it by now. I will see
Thanks alot for your help and encouragement.
Lapping such asymetrical parts isn`t something for the faint hearted.

I always say: Support your local businesses. If there`s a shop with a honing machine and the owner has a good rep, spent some dollars!

I ordered the wrong rod-bearings. So I`m not finished yet. After receiving the correct ones I will have to lap a lil more to achieve a proper plugfit and subsequently the right running fit.

Thanks again
rainer

Another hint one or the other might find it helpful.
When pushing/pulling the rods over the laphead it helped me alot to reduce the bellmouthing/tapering substantially when I work with my upperbody. I do not extend my arms and I`m not pulling my arms towards me. So the angle of my elbows stays the same.
Works for me.

I know pro machinists are shaking their heads reg safety. All true.
Beware of the tunnelvision while lapping such asymetrical items,you need to be highly concentrated but think ahead for your exit strategy, to retreat in a split moment when the rod becomes too tight. Don`t fight the rod.

Rainer,
I'm not sure where you are in Germany, but working on HD motors requires lots of very specialized tools and knowledge. Many are hard to find now and expensive when you do. In Europe everybody wants to sell you new assemblies and new parts. Very few people in all of Europe do what you need. It was very hard for me to believe, but it is true. This stuff is just not being done anymore here. However, I have found a real GEM. His name is Willem Been. He has a small shop in Almere-Stad in Holland. Google WB Mechanic- Motorbike dealership - Almere-Stad. His phone number +31-36-546-5481. Willem is the real deal. He's 69 years young and still drags a nitro burning twin.

PS
I don't know how old "Ole Harley" is, but I have on the shelve a brand new set of EVO con rods with matching bearings and crank pin that I don't need. I'll make you a deal. Send me a PM if you have interest.

""Another concern is trueing the lap. Quite annoying cause I fixed the lap in a collet and centered it with the tailstock. So it was true however after adjusting it altogether maybe a .002 (in many tiny steps each maybe 1/32 turn of the nut) the laphead was out of true again (not the mandrel). I suspect that compound drippes onto the tapered mandrel and after readjusting the laphead the mandrel wears off. The dial prooves it.
So I shaved the laphead with a sheartool again.""

This job has become very difficult for you because you are using the wrong tool. The Jims tool was mistakenly designed after a Expanding Mandrel not an Internal Lap. The best solution is to contact one of the lap companies in the USA. Either American Lap or Helical Lap can set you up with the correct tools.

Everytime you adjust the tool there is going tobe a problem.

Good Luck.

If you're going to be rebuilding Harley lower ends, you're going to have to have a Sunnen honing machine. How do you size the pin bushings? I've never tried lapping the rod races, but I know you can do better than .00015 per side with a hone. Remember, the rollers come (or at least they used to) in size increments of .0001, so if you're off by .00015, you're rod is going to corkscrew to one side and tear up the flywheel thrust washer ( if they still even have thrust washers!)

Hi

almost forgot about it.
When I was almost finished with lapping I somewhat screwed up. As a consequence I needed to replace the races in both rods. To press them out and new ones in I turned some closefitting tools.


To my surprise the new shells showed a pressfit of .006 inches. So I used dry ice and heat to press in the new ones.
The buildup of compound to the right and left of the race while lapping still concerned me and I finally cut a groove into the laphead, basically a huge thread, using a standard threadcutting-tool HSS.
Some wet sandpaper and finally another go with the sheartool produced this:



It works like a charm. No more buildup of the #320 compound. No more grabbing. No more stackplate needed. Particular the front (male) rod which tended to bellmouth easily. Wonderful cylindrical races within .00008 inches. Both rods (altogether 3 races) are perfectly round and of the same size. Hate to say it: Instead of hydraulic oil I used honing-oil. It makes a huge difference, imho.
After 10 weeks = Races done.
LOL