New project Introduction and questions

I found the main bearings came out of the cases with no interfierence fit, but the new Andover bearings were a little bit bigger and interfierence fit is restored. The old bearings od are 3 or4 thousands smaller.
 
Ok. Redo. Learned quite a bit in the process. First, I calibrated my mic. It was a little off. Second, I was holding it too tight against the journal. Watched a ton of videos.

I have one journal at 1.749(44.433mm) and the other at 1.748(44.420mm).

Given that info, can I use standard bearings or do I need undersize bearings? If undersized then must the journals be reground?
 
My crank journals are similar to yours so I polished them up and will fit the connecting rods and see how they move when doing a drop test. Thats when you let them fall under here own weight and see if they are smooth and not to loose or tight. I bought standard. I am also no expert.
 
That was going to be my next question: Plastigauge.

The used bearings I pulled out are standard and they are worn, I'm sure. How can I accurately verify using Plastigauge without new bearings on hand? Its not like I can purchase them, verify, and then return if they're not right.
 
You are correct you would have to buy the bearings to check with plastigage. With the second set of numbers you are now just slightly out of low side spec of 1.7500 by 1 and 2 thou. You might be able to get by with this with standard shells as long as the crank is not scored. Also are you checking in multiple position to determine if the wear is oval. You must regrind the crank to use oversize shells. Recommended clearance on the bearing to journal is 1 thou. Do you have a workshop manual? Commando cranks must be ground with a radius (see manual). Most automotive machine shops are reluctant to do this because it is not common practice now and they have to specially dress the stones to do. My recommendation would be to take it to an automotive machine shop and have them measure it and inspect it. You can show them the grinding proceedure but you may have to send it to a Brit bike shop to have the actual work done.
 
Yes, I checked it from multiple positions as well as the middle and ends for any taper. I was just curious how people use the plastigauge without new bearings on hand. It wouldn’t make sense to do it with used bearings.

After reading some more it makes more sense to me now. That’s what the regrind specs are for. Thanks!

There’s an engine shop near my work. I’m going to stop by and see if they can verify my measurements for me. I don’t think it’ll need any work, but i do have the workshop manual handy for the radius specs
 
Ok. Dropped by an engine shop. He measured 1.7499 on one journal and 1.7487 on the other. I took my used bearings with me. He used plastigauge and torqued to 25 ft-lbs and they showed .001 and .0015 on the strip. Crank was good. No scoring, no oval, and good polish. Advice was given to run a new set of standard bearings, new con rod bolts and nuts, and it will be fine.

Now that I understand how this works, and re-reading everyones comments, my question of undersized bearings answered itself.

On to the cylinder heads now.
 
I was cleaning out my oil pump since the case had some sludge and I wanted to make sure none had gotten trapped inside. While doing so I noticed these two shims, but didn't see where they came from. I don't think they were inside, but I could be wrong. Maybe behind the seal? I looked up some videos and checked the workshop manual, but cant find anything. Any thoughts?

Shims
 
Yes they should go behind the seal if required which I assume they are in order to give the correct seal compression.
 
I would not have thought a Commando engine revs fast enough to ever need a crank regrind. Especially when they always stay at home hiding in their shed, where they are safe from speed cameras.
 
rv1890 said:
Got the crank separated. Cleaned out some sludge, but nothing too crazy. Journals look great. Just hit them with some polish.
The journals measure 1.739 and 1.744. The bearings I removed were stamped with 23255 lower and 25384 upper. The internet tells me that's standard size. With those journal measurements do I go undersized now? My initial guess is either .010 or .020, but not sure.

Crank Photo

Also got the cylinder torn apart.

Cylinder Photo
Click to expand...
If you measured with a caliper, get a micrometer. Your measurement are quite undersized for standard shells and if the shell and journals look good that much wear would surprise me. Also, .005" difference in the two sides is huge and very surprising. Any idea how many miles are on the bike?
 
@marshg246 You're correct. It was my measuring skills that were off. I took the advice of one of the users on the forum and took it to a machine shop. The updated, correct measurements are listed above. Satisfied with the results and learned something in the process. :cool:
 
rv1890 said:
Ok. Dropped by an engine shop. He measured 1.7499 on one journal and 1.7487 on the other. I took my used bearings with me. He used plastigauge and torqued to 25 ft-lbs and they showed .001 and .0015 on the strip. Crank was good. No scoring, no oval, and good polish. Advice was given to run a new set of standard bearings, new con rod bolts and nuts, and it will be fine.

Now that I understand how this works, and re-reading everyones comments, my question of undersized bearings answered itself.

On to the cylinder heads now.
Click to expand...
Great!

Generally new bolts are not required - new nuts must be used.
 
Unlike modern rod bolts that are often torque to yield and should not be used again, Norton bolts can be used again. New nuts though.
 
Next step. Piston ring gap. I'm using Hepolite pistons with their rings. PVD faced top compression ring, cast iron second compression ring, and two piece oil ring.

Can someone confirm my math? My bores are .060 over.

2.874 (standard) + .060 over = 2.934

If the rule of thumb is .004-.006 gap for every inch of bore then:

2.934*.004 = .0117
2.934*.006 = .0176

So I should be setting the gaps between .012-.018 on the first and second rings, correct?
 
rv1890 said:
Next step. Piston ring gap. I'm using Hepolite pistons with their rings. PVD faced top compression ring, cast iron second compression ring, and two piece oil ring.

Can someone confirm my math? My bores are .060 over.

2.874 (standard) + .060 over = 2.934

If the rule of thumb is .004-.006 gap for every inch of bore then:

2.934*.004 = .0117
2.934*.006 = .0176

So I should be setting the gaps between .012-.018 on the first and second rings, correct?
Click to expand...
The ring gaps are in the workshop manual - no need for math. Generally, I have not needed to adjust them at all with Hepolite complete sets. I only would if the gap was too small, but it never has been.

BTW, yes, the oil rings are hard to get in the cylinder. DO NOT "adjust" the spring - they come correct!
 

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