[homedad]

My son has shown some interest in the older Hondas so we found one about an hour away. Checked it out, no smoking, no leaking, idled good, oil looked good and it felt good on the test ride. We bought it and insured and registered it. Got on it to take it to a closed parking lot for him to practice on and I get this pop and a loud racket from the left cylinder. It reminded me of the time I blew the spark plug out of an old CL 175 back when I was a kid. No smoke just loss of power and struggling to keep running.
I did a compression test and got only 65 and 70 LBs. I ran an inspection camera and found something shiny inside that left cylinder which I thought was a piston ring. I also had done a 60PSI pressure test on that cylinder and you could hear the air rushing into the crankcase. After taking the head off I saw that it was a screw which became so hot it welded the head to the top if the piston. To do a better inspection I pulled the cylinders off and that left piston's wrist pin is nearly seized. It barely moves. I had to use a giant C clamp and 2 sockets to press it out of the piston. The rings look good. The head gasket was intact and the piston had no hole in it. The cylinders are still smooth and I obviously need to replace that piston and rings. One question I have is why was the pressure leaking into the crankcase so quickly if the piston, rings and valves were all functioning? Is that normal under sustained air pressure since its only designed to contain quick explosions? Also I would prefer to only have to replace that one piston and ring set. Would you hone that one cylinder and replace the piston and rings or do both. I also need to find where the screw came from. I'm guessing the inside of the left carburetor. Thanks for the help

 

[ancientdad]

Strange story, indeed. I suspect that you might see something more wrong with the piston with a cleaning in a parts washer and closer inspection afterward, since it's hard to understand the loss of seal if all the components are seemingly in good condition. Did you change the oil in it before riding it more than the test ride? I wonder if the PO was in the habit of turning off the fuel when the bike was parked - 450s are famous for slight overflow weepage from the carbs trickling its way past the rings and into the crankcase, diluting the oil and causing a multitude of lubrication issues as a result, which could explain the left wristpin tightness. Highly possible that the PO rebuilt the carbs to get the bike running and re-sell it, and did a poor job of re-assembly resulting in the screw coming loose from one of the butterflies or choke mechanism. Are you sure it was on TDC compression stroke when you tried the pressure test? If it was on overlap, the rushing air sound could have been misleading. Unless you plan to re-sell the bike, I'd do both cylinders while it's down and check the valves as well, lap them in at the least, and based on the typical history of the DOHC valvetrain, carefully inspect all the cam lobes and followers for wear too. These engines are pretty tough and durable when properly maintained, but they have a few quirks that need to be attended to properly to get the most out of them.

 

[mike in idaho]

I've always made it a policy to NEVER disturb throttle plate screws unless it is absolutely necessary, why ask for trouble? Were the rings still free in the grooves? That screw bouncing around in the cylinder may have hit on the edges, deformed the outer piston dome, and pinched the rings. They need to be free in the grooves to seal. I would replace the pistons as a set so they match, weight-wise.

 

[Rscottp]

I just got the same bike and when I drained the oil it was 90% gas, It was coming out so fast I thought it was going to overflow my oil drain pan(lucky it stoped before overflowing all over my lawn).

 

[homedad]

When I checked the oil at first look it was normal viscosity but too clean. It made me a bit suspicious. Anyway as I'm working on it and the oil running out looks the same and isn't diluted with gas. I was considering the valve lapping as long as I've got it all apart. for the price of another piston I guess I'll do it. Is honing necessary with new rings? And where do you get your internal engine parts? A friend who rebuilds recommended davidsilverspares ohiocycle and classichondarestorations.

 

[mike in idaho]

Always hone when you install new rings, clean the bores really well afterwards. Hot soapy water(no solvent or gas) until it's CLEAN. Oil the cylinder right away or it will rust right before your eyes.

 

[homedad]

Thanks for the advice.

TDC yes I did a visual with the inspection camera looking at the piston and valves. Piston at the top and all valves closed.

 

[homedad]

Any ideas on sources for pistons? I see them anywhere from $70 to $160 per piston kit.

 

[homedad]

I just checked the carb, the piston and the connecting rod. Looks like one of the 2 screws from the throttle butterfly is gone. I checked the rings on the piston and the top ring and the oil ring won't spin around the piston. They are stuck in the exact spot where the screw welded itself to the piston. My new problem is that the good wrist pin won't slide through the hole in the connecting rod smoothly. I could get it in there but it's not smooth and won't rotate. Do I need a new connecting rod or can I get that fixed at a machine shop? I rechecked the cylinder walls and can find some scratches if I use my fingernails. Is this now a bore rather than a hone? Just can't feel them with my finger tips.

 

[ancientdad]

It's not uncommon for the small end of the rod to be affected by the excess heat from what happened to that cylinder. The rods are not replaceable like common connecting rods, these cranks are pressed together and the big end of the rods have needle bearings instead of inserts. You can usually use emery paper on the small end of the rod and clean it up, depending on how bad it is. If it can't be cleaned up, your best option will be a used crankshaft. Getting the cylinders measured will determine whether or not you'll have to bore it. If they're within specs for clearance, new stock pistons and rings (assuming it's never been bored previously but again, once they are measured you'll know) and a good hone will get you going again. Do you have the Factory Shop Manual? If not, someone here can get you a link to it for the proper clearances

 

[homedad]

Good info. Thanks

 

[homedad]

Thanks that's helpful

 

[ancientdad]

Found the link to the FSM

https://docs.google.com/file/d/0B_ZumJE59-T4YjUwNjllMjgtZDNlYi00ZTcxLTgyNDEtZmIxOTlmM2ZlNTZl/edit?ddrp=1&hl=en

 

[homedad]

Thank you ancientdad, that’s very kind of you.

 

[homedad]

Okay I got that connecting rod small end nice and smooth to where the wrist pin slides in as slick as the good one.
I took my cylinders in to a local machine shop and the guy said that I need boring so buy the pistons for a .50 oversize bore and bring them in prior to the job. I just got the pistons and flipped them over on my granite counter top along side my old good piston and noticed that I can't simply push that wrist pin directly into the hole in the new one without lifting the old one slightly. This to me means that the new pistons will have clearance issues with the valves and spark plug. Is this normal and do I simply put in multiple head gaskets?

 

[LiamG6]

Did you buy NOS cast pistons or forged Wiseco's etc? The forged pistons usually are slightly different, shorter skirt length and clearance cutout for crank and they may be slightly higher compression, the valve pockets might be slightly deeper if they are higher compression to provide valve clearance because of the higher dome. The main thing you need to be sure of is deck clearance, ie the top outer edge of the piston should be the same or within 0.5mm of the original cast piston. You can measure from the top or center of the wrist pin to the top outer edge of the piston and compare them both.

If you bought specific CB450/CL450 pistons they should fit without any issues. If you need to adjust the deck height use thicker or thinner base gaskets or 2 base gaskets, only use 1 head gasket. You should not have any clearance issues if you bought the correct pistons though despite slightly different design.

 

[homedad]

I bought the Wiseco pistons that you describe. That makes sense about the valve pockets compensating for the differences. I'm going over to the machine shop this morning. I'll see if the guy has any helpful information re. this. The information I had was from this video at around 25:00

Thanks.

 

[ancientdad]

Just my 2 cents, as they say, but I've never shimmed spark plugs. The overbore or high-compression pistons I've used were designed for the engine they were going in and fit properly with doing something like that.

 

[homedad]

Yea that's what the guy at the machine shop said.

 

[homedad]

Anyone know if I still need to hone my cylinders after I had them bored?

Also does anyone know where the small o-rings go? are they all between the head and cylinder?