Need to go with oversize wrist pins in my CB77. I'm going to have a machine shop do the pistons on their Sunnen, but I want to do the rods in the engine by hand. I was thinking about using an expansion reamer to get close and make sure they're round, then maybe a brake cylinder hone or ball hone to finish it. What have the people who have done it before used??? Thanks in advance for any advice and experience!
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Best way to enlarge small ends
I don't think it's practical to mount the whole crank in the Sunnen. I don't want to press the crank apart, I'd rather just replace the whole assy if I have to. The Harley guys ream those bushings in place all the time, at least they say they do with clamps and beer... Seems like the adjustable reamer would pretty well follow the hole with a light touch. Only taking 1-2 thou off the surface. How far off could it get?
What was the official Honda procedure when they introduced the oversized pins??? Doubt they wanted the cranks pressed apart just to ream those bushings.
Hi,
I don't want to be negative or offensive in any way, but I have to make some critical statements about reaming the small ends by hand, before this method is copied by others with some possible serious long term (and expensive) consequences as a result. Reaming by hand never gives the precision that's needed for the small end, and reaming with a sunnen with the conrod still mounted is difficult because there is no good (reliable) reference. It simply isn’t possible this way (without disassembling the con-rod) to find a good reference surface one can use as reference for the alignment within the specifications and precision of the bore. Remember, the small end bearing is the most precise application in the whole engine. It’s not that I don’t believe that one can bore to a correct diameter, because that isn’t the difficult part. The really difficult part of this bearing is the alignment toward the crank axis (both). If the bore is more than a few 0,01 mm misaligned in any direction, the damage will be severe after running the engine for a few thousands of miles. What will happen when there is a misalignment? Will it seize? No, not directly, actually it will run fine, as long the misalignment isn’t too big. Will there be any quick wear at the small end ? Again, no. So what happens then? To see what happens one should look and understand the forces from the conrod to the piston and the other way around. If there is any misalignment, the piston won’t be pushed up in a straight line by the crank, same for being pushed down after the expansion of the gas. With every revolution the piston pin will be pushed toward one side of the cylinder wall, pushing the piston to one side of the cylinder wall, every revolution again and again. The piston pin also hammers to the little clip, and eventually this clip will give up with the result of seizing the piston in the cylinder, or deform the groove so much that the piston will have asymmetrical wear, and also eventually will seize. The lay-side of the piston and cylinder will be under asymmetrical load and wear out quickly and start making noise (piston to cylinder clearance issue’s), and will result in loos of power and excessive heat. The big end bearing is also being under asymmetrical load, and will wear out quickly, so are the main crank bearings. The same happens when people are hammering the piston pins out the piston, the con rod is bend just a little (not visible with the naked eye). In the end the engine is noisy, eats pistons for breakfast and piston clips will mysteriously come out, or are impossible to get out because it is hammered into the piston groove. Piston pins are hard to remove from one side because pistons are deformed one side etc. etc. etc. Again, you won’t notice these things within a few hundred miles, but eventually it will happen. I disassembled many engines, and many crank bearings and big ends are destroyed this way, so are the small ends. It’s easy to tell when it was an oil problem or an alignment problem which destroyed a crank, the wear patterns are different (symmetrical versus asymmetrical). It’s very difficult to find a good used crank. Of course, lubrication issue's are a reason, but don’t underestimate the reasons I described above. When your piston pins are hard to remove, think twice, because when new, the piston pins slide in and out by hand. I advise everyone who wants to walk this way, to disassemble the con rods for boring in a proper way. Jensen assembly of Japanese motorcycles requires great peace of mind (Pirsig)
Hi,
It's an advice, nothing less, nothing more. In the end, you are responsible for your decision. Now you at least know what those consequences could be and why. The problem is that following advices on forums can ruin your bike. Most of these advices are written with the basic idea, "Why doing so difficult if it can be done much easier (cheaper) ?". Nothing wrong with short cut's IF they're working and good, but who 's going to judge ? And who is paying the bills when things go wrong or not working out as promised or expected ? If I deliver my crank at a specialist to do this kind of work I expect a correct alignment within plus / minus 0,005 mm, because that's why I pay him for. You can do with this advice what you like, just as any other advice you can read on the internet, and if you don't like the advice you read, well, we living in a free world after all. But don't forget : you were the one who asked, and if you were certain about the method you suggested yourself, why did you ask in the first place ? Maybe you don't like the answer I gave (and Tim), because there's a lot of work and money involved for something that seems to be so simple, like you argumented yourself. Well, I'm giving you the above advice, because that's what I think about it, it's my opinion and experience, No hard feelings when you're deicide to do it the way you suggest, but it's not something what I should do, Jensen assembly of Japanese motorcycles requires great peace of mind (Pirsig)
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