Honda Twins banner

1 - 4 of 4 Posts

·
Registered
Joined
·
27 Posts
Discussion Starter #1
I'm pretty sure I've only posted on these forums once 2 years ago to introduce myself when I first got my 1972 CB450, but I've been slowly working on restoring it ever since, using the wealth of information there is to be had here.

Last summer, I had my engine top end assessed by a local machine shop. They recommended I have it bored out, so I purchased NOS 0.25 over-sized OEM pistons from David Silver Spares, and got a set of NOS rings to match them from an ebay seller (JTMarks, I believe). I dropped everything off at the machine shop and they took care of the cylinder boring. It took awhile and I didn't get everything back until fall and I never got to rebuilding the engine until now.

Last week, I got the bottom end all put back together and today, I began putting the top end together. I put the rings on the pistons, then put one wrist pin clip into each piston, lubed the wrist pins lightly with assembly lube, then slid them in partially. I installed one piston onto its connecting rod, pushing the wrist pin in all the way, and installed the other clip without any issue. When I went to do the same with the OTHER piston, I couldn't get the clip installed -- well, I COULD, but the ends of the clip where overlapping like it wasn't seating properly. I inspected the other 3 clips, and they were all seated with a small gap between the ends. I removed the clip and tried again, same deal. I thought maybe the clip (I bought all brand new ones) was defective somehow, so I tried one of my originals and got the same result.

Ultimately, I took the piston back off of the engine and tried to get it together just on my work bench. Without the wrist pin, the clips go in just fine. When I put the wrist pin into the piston, I can't get the second clip to seat properly. I've basically concluded that either the piston wrist pin "hole" is too narrow, or the wrist pin itself is too long -- by just a wee little bit.

So my question is -- has anyone ever run into this before? Would it be completely ridiculous for me to just grind (or even sand) a little bit off of the end of the wrist pin to shorten it to fit (it's gotta be like some fraction of a millimeter that has to come off)?

I'm using the original wrist pins -- I didn't get new ones and the machine shop said they were in good shape. They look perfect. After searching for help on this subject, I found some conversations about different wrist pins being used for over-sized pistons. Should I NOT be using the originals?

Thanks in advance for any help or advice. I'm just a novice mechanic, and this is my first engine rebuild.
 

·
Premium Member
Joined
·
10,203 Posts
I would remove the other wrist pin and measure the 2. If they measure the same try installing the wrist pins in the opposite pistons. This will tell you whether the problem is the wrist pin or the piston. It's apparently not the clip. In any case I would talk to the machinist before making any modifications.
 

·
Registered
Joined
·
27 Posts
Discussion Starter #3
I would remove the other wrist pin and measure the 2. If they measure the same try installing the wrist pins in the opposite pistons. This will tell you whether the problem is the wrist pin or the piston. It's apparently not the clip. In any case I would talk to the machinist before making any modifications.
Thanks for the ideas. I'll measure the wrist pins this afternoon and possibly try swapping them between pistons. Now that I think about it, the machinist had the wrist pins inside the new pistons when he packaged everything up to return it to me last year. Maybe there was a reason for it haha. I didn't keep track of which pin was in which piston when I started putting things together yesterday.

I was also thinking about it and I never tried swapping out the OTHER clip on the trouble piston (the one I installed first). I'll be checking that as well.


Sent from my Nexus 7 using Tapatalk
 

·
Registered
Joined
·
27 Posts
Discussion Starter #4
It was the clip.

I measured both wrist pins and they were exactly the same length. I swapped the pins and, for kicks, just used my original clips on the piston where things weren't fitting properly and it all went together perfectly! I narrowed it down to being one of my clips -- it had a little bit of a kink at the end of it that was preventing the wrist pin from going in as far as it should (at least that's what I believe was causing it). If I use any other clip, it works fine.

Phew! Glad that's over. I really didn't want to have to deal with grinding wrist pins or replacing pistons.
 
1 - 4 of 4 Posts
Top