Honda Motorcycles - FireBlades.org banner

Engine knock

7K views 37 replies 9 participants last post by  cbrmatt88 
#1 ·
Well after 78,000 fun miles the ole girl is having the first major tear down. Aside from a missing 4th gear that needs repair, a knock developed after some serious sustained high speed riding. Pulling the oil pan and strainer proved to me one of the journal bearings is coming apart. I can't see any discoloring of the crank or rods so I'm crossing my fingers no case or crank issues arise. I'll drop the motor this weekend and post some pictures once I find the issue. I'd attach a video of the sound if I could figure out how...
 

Attachments

See less See more
5
#2 ·
Looks like you acted just in time. If I had to bet, I'd say it was one of the outside main bearings, I've had 2 go on 2 different blocks. Seems to be a weak point. I've tried to mitigate it happening again by taking as much weight off the pistons and rods as I can, and matching all the weights of the reciprocating components as accurately as I can. Makes for a much smoother running engine.
 
#4 ·
No damage whatsoever to cases, they're protected by the shells, as are the conrods. I did like you and wrecked the bearing AND copper backing, so the crank got a slight coppery mark on it but polished right out with almost no effort. No measurable wear or ovality.

I did nothing to the crankshaft, just took meat off the pistons and conrods so as to increase (make bigger) the various stressed radii. Took a little out of the lightest components, and more out of the heavier ones to get everything to line up within 0.5 gram. The piston skirts are already as short as they can be, so they were left.
the rather strange thing was that I found that the new mainshaft bearing for the location which had failed, despite being ordered according to the stamped codes on crank and cases, was a little tight when I measured the clearance with Plasti-gauge compared to the others (why did I check it? because it was the second time it had happened with that block and I wanted to find out why) So I ordered a suitable size to correct it, and since then no problem.
 
#7 · (Edited)
Cases split and some damage is confirmed already. More shift fork issues, I need to replace 4th gear and its corresponding gear. I haven't pulled the connecting rods yet but the mains are obviously damaged. I took pictures of the crankshaft because the one does not have a groove down the center or a whole drilled. As far as I can tell from other pictures it's not supposed to be but it is the only one that doesn't so it looked wrong at first glance.
 

Attachments

#12 ·
I am taking the cylinders and crank to a machine shop Thursday to hone the cylinders and measure/polish the crank. They charge $35 to hone and $30 to polish. I ordered some great looking camshafts off eBay yesterday for $45. I can't decide if I want to lap the valves myself or not. They charge $180 at the machine shop to lap the valves and replace the seals. I know someone with the kit I just don't know if it's worth my time or not. I'm going to build a parts list tonight and see where I'm at.
Ps: all con rod bearings are perfect, will replace anyways but they looked like new.
 
#22 ·
My cylinders look a lot like that, I think all of them do to some extent. There are a few deep scratches the guy at the machine shop was concerned about but he is going to let me know. He said it's usually poor filtration, I know the bike had a K&N in it when I got it and I hate those air filters.. when you hold that filter up to light you can see right through it, even new. I prefer a stock filter that can't be seen through even with a flashlight.
 
#24 ·
This cylinder scoring issue surfaces now and then. It has been discussed in many threads before this. All of the ones using Hondas version of alusil look like that. It can still give good compresion readings, not drink oil and work just fine. Normally when the wear on the plated piston skirts and alusil bores get too big the piston will start to slap. At first cold and then gradually it will get worse and start to slap all the time even when engine is at operating temps. In my case when that happened everyting ellse inside the motor was at that condition it needed changing. I got the bores plated, new pistons with rings, main and rod bearing clearences were over the service limit, shift shat and 2 shift forks, all gears needed cutting, new clutch and head was done at the same...
 
#26 ·
The pistons failed measurements, machine shop says the skirts are collapsed .001" beyond specifications. Can't decide if I want to even rebuild this thing anymore. They have been busy at the shop so I'm not sure about the crankshaft yet, that will probably be the deciding factor. I was planning on replacing the oil pump purely for safe measure anyways. I picked up a cheap bike in the meantime, 08 FZ6 for $600. Heck of a deal if you ask me.
 

Attachments

#28 ·
Sorry it's been a minute, this build is gunna be slow. I got the cylinders back with a fresh hone. Crankshaft measured good and the journals were polished. I remeasured the pistons today and consistently got 73.96mm to 74.00mm on the skirts so I'm going to get new rings and reuse them (spec is 73.90mm). I also got this transmission off eBay for $135. It's in wayyy better shape then mine, I just think my gear dogs are too far gone, I don't want to do this again. I'm thinking about sending the new transmission out to get undercut, any opinions on this?
 

Attachments

This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top