thoughts connecting rod free play?

Doing a refurbishment of pistons, cylinders and head, and trying to determine if I should split the cases and do the lower end as well. Is there a way to get an indication of main bearing condition by con rod play? I ran across a thread on a Harley site by a guy with a Shovelhead who had the same question. General consensus was 3 to 4 top end builds to 1 lower end build. Should be zero discernable up and down play. One guy who calmed to be a long time engine builder suggested putting in a wrist pin and see if there was any play by twisting it. Naturally I would rather avoid the lower end work and just put it together and ride it. Any thoughts on the subject appreciated.

The proper way to measure is to use Plastigauge, a soft round piece of a material with a precision diameter. When you place it between the shell bearing and the journal and torque the nuts up to spec it spreads out, dismantle and the measure its new width and then compare to a table and read off the clearance.


If you use the old bearings then the clearance will include any wear in the shell thickness, but if you use new shells then you could find the journals are worn and you can no longer use the new shells.

By the time you feel discernible play its way too late, that will be 3 thou plus before you notice and you are looking for 1 to 1.5 thou.

The NOC notes refer to 2 sets of rings per piston but no ratio on rebores to crank regrinds.

fid04 said:

Doing a refurbishment of pistons, cylinders and head, and trying to determine if I should split the cases and do the lower end as well. Is there a way to get an indication of main bearing condition by con rod play? I ran across a thread on a Harley site by a guy with a Shovelhead who had the same question. General consensus was 3 to 4 top end builds to 1 lower end build. Should be zero discernable up and down play. One guy who calmed to be a long time engine builder suggested putting in a wrist pin and see if there was any play by twisting it. Naturally I would rather avoid the lower end work and just put it together and ride it. Any thoughts on the subject appreciated.

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No.

Harley's have ROLLER BEARINGS.

Your question asks about determining main bearing condition via con rod play which can't be done. I think you mean big end play. Note the rods will rock slightly with brand new shells on a newly ground crank, but only very slightly. After many miles the rock will be greater, but what's more important is true up and down play. If you grab the rod and try to pull it straight up and down, the play should be negligible.

A fresh motor will have no discernable movement, but a tiny bit is ok. If you notice one is distinctly worse than the other, I'd tear it down. Not very scientific, but if you've felt a few, you know when it's time to tear it down.

Do you know the oil pressure of this motor when it was hot with the correct oil, and temperature plays apart. I am sure someone will chime in to tell us what it should be, maybe 45psi or something, and idle hot 15psi, ?.

I have severe doubts about oil pressure in Norton twins. Mine has not exploded yet, so it must be OK. If you can rock the rods sideways on the crank by holding little ends you probably have too much clearance on the big ends. If I was rebuilding a motor, I would pull the big ends apart and make sure they are right, and I would also replace the main bearings.

If you are going to rebuild the top end, then why not go further and do the bottom end as well, I am sure the conrod bearings will have sign of wear on them, the main bearing should be right (but still replace them) but the slipper conrod bearings do wear, every Norton motor I have pulled down has always had signs of wear on the conrod bearings, some more than others.
To me it's not a problem splitting the cases and putting them back together, so with me why only do 1/2 a job, best to be safe than sorry later down the road and that way you get to check on everything down below, this is my opinion and even low mileage motors do show some wear on those little end bearings, cheaper to replace the bearings with slight wear than doing a crank grind.

Priming the crank after a rebuild avoids needless wear on those big end shell bearings

BERT said:

Priming the crank after a rebuild avoids needless wear on those big end shell bearings

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Well that's part of any rebuild, with all my bottom end rebuilds everything is lubed with a 50/50 mixture of STP/motor oil on assembly and after run in I also run STP mixed in my oil and have done so since I done the conversion to the Featherbed frame back in the 80s.

I had the same thoughts as you when I pulled my top end off. Glad I decided to go deeper.

fid04 said:

Doing a refurbishment of pistons, cylinders and head, and trying to determine if I should split the cases and do the lower end as well. Is there a way to get an indication of main bearing condition by con rod play? I ran across a thread on a Harley site by a guy with a Shovelhead who had the same question. General consensus was 3 to 4 top end builds to 1 lower end build. Should be zero discernable up and down play. One guy who calmed to be a long time engine builder suggested putting in a wrist pin and see if there was any play by twisting it. Naturally I would rather avoid the lower end work and just put it together and ride it. Any thoughts on the subject appreciated.

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Since the rods have a good bit of side to side play it would be difficult to tell if there were any up and down play. You might be able to rig something up with a dial indicator but by the time you've done that it would be easier to take the bottom end apart.

You didn't say anything about what engine - 750/850. If 750, is there an oil filter? If no oil filter then you need to split the crank and clean it out anyway. Most likely the oil pump needs service so taking the timing side apart is not a big deal once you're in there. If you're experienced with taking the primary apart, then that's a pretty quick job.

When I do a bottom end, I always use new shells, I always check the journal holes - often 2-3 of them never were countersunk, some were not well drilled and have a chip of metal in the inside so I always take the crank apart even though with an oil filter there's normally little to nothing to clean out. You must use new nuts but the conrod bolts don't need to be changed unless damaged or rusted. So far (knock wood) I've never had to have a Norton crank turned. Minor scratches that don't stick up hurt nothing IMHO. Of course if heavily scored then they would need to be turned or if they measure undersized. Honestly, if I had one needing turning, I would buy another on eBay or use one of my donor engines as I have no machine shop to do that and Jim Comstock is so backed up that he takes forever.

Of course, you can just take a chance - if too loose it will come apart while riding at some point but probably still has a long way to go but hoe many miles are on the bottom end.

When you have the cylinders off, inspected the tappets and cam carefully - if they are well worn then it must come apart/

No Norton expert here, but when I was checking out the new to me 850, I saw the speedo had 7600 miles. Pretty low.
I had a tolerable rod axial, or side to side play. The crankshaft side to side play was within tolerance, and the cam play was around ten thou as I remember. I had no discernable up and down rod play. None. I squirted oil into the oil feed bore on the crank and it escaped out the side of the rods at what seemed an evenly reasonable rate. Real seat of the pants stuff here.
I decided to go with it knowing I may have to tear down completely. I currently hold 30lbs when hot at highway speed. Around 22 at hot idle. Just my 2 cents worth of experience. Of course always better to renew shell bearings.

Thanks to everyone for their input. General consensus seems to be, just bite the bullet and split the case. That was my first inclination, but I was seduced by the idea of being able to get away with something, which rarely happens in my life. It will be a first for me, and satisfying if the whole project comes out good. Bike appears to be a 70' that was titled and sold in 71'.

Shelby-Right said:

Do you know the oil pressure of this motor when it was hot with the correct oil, and temperature plays apart. I am sure someone will chime in to tell us what it should be, maybe 45psi or something, and idle hot 15psi, ?.

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No idea

Shelby-Right said:

Do you know the oil pressure of this motor when it was hot with the correct oil, and temperature plays apart. I am sure someone will chime in to tell us what it should be, maybe 45psi or something, and idle hot 15psi, ?.

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Hot day, hot engine, 20W50 conventional, idling at a stop light you will see 3-5 psi and at highway speed 30-50psi depending on many factors. That's why oil pressure gauges can drive you crazy! Max pressure depends on you oil pressure relief valve and how many shims and the spring and piston conditions.

I use the Don Pender oil pressure switch on all my builds connected to the red warning light in the headlight and as long as it stays off at speed, I'm happy. At a traffic light when hot the light will tend to flicker on and off as the switch is factory set for around 4psi. Many oil pressure gauges will show 0psi in that condition but it does not mean that it's really 0psi just that it is not designed to detect that low.

You will never be able to detect up and down play at the rod ,as said earlier in this post it's not a roller bearing big end
However you can feel for play by rocking the rod on the journal
This shouldn't be confused with side to side play and is hard to describe but easy to do
Take hold of the Conrod with both hands and whilst holding the bottom of the road so it doesn't move side to side you can push and pull the top of the rod with your thumbs
Ideally it should have almost zero or very little rock

IMO… just look at and around the bike…

Why are you stripping the top end? If it’s because everything is utterly worn out, that’s an indicator that the bottom end might not be far behind.

What mileage does the bike have? The higher the mileage, the more bottom end wear, etc.

A good look around the bike and the application of some common sense will go a LONG in making a decision.

Add to that your intended use, and the decision will almost be made automatically.

i.e…

A low milage original condition bike, being recommissioned for gentle club runs and Sunday rides is likely to need very little.

Whereas a high mileage bike that’s had a hard life and is being rebuilt into a hot rod that will see 7000rpm regularly needs a full strip down.

Mr Tedious here. Take it apart , all the way apart. Measure it with a mic. Since it is apart you get to do a serious inspection and clean. The bother of all this pales when compared to the easy overhaul and a loud noise or
a bike that is always a worry.
You don't know until you know.

MikeG said:

Glad I decided to go deeper.

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A lot of wear hence the leaded bronze layer is visible, which it should never be. But also look at the score marks in the centre, the oil has been very dirty and circulating debris has scored the bearing.

Strip the bottom end, crank as well, clean the sludge trap out (The void in the middle of the crank). Then inspect the bolting flange faces. You will find evidence of the crank center (void) has been leaking oil

This is a 750 crank cheek and flywheel.
The grey area nearest the crankcase flange is where the oil has scoured the face as it has been forced out of the crank at high pressure. Every crank i have stripped and rebuilt has displayed this problem to a greater or lesser degree. Even from as low a mileage engine as one with 13k miles on it. This leaking robs the bigend shells of the oil it needs, its no wonder it is almost always the drive side big end that lets go when oil delivery is a problem, it is starved of oil when things get worn.
Seal the flanges with a smear of loctite when assembling and reverse the big end shells to block the oil squirter hole, and most importantly, close the clearances up in the oil pump to zero. Your bottom end will outlast you then.