running a cylinder with no pipe for a few minutes

[Randall]

I pulled the right side cover on my CM450E to get to the clutch and chain balancer. Clymer said to remove the exhaust pipe, the Honda FSM makes no mention of it. Clymer got to me first, so I removed it, and in doing so wrecked the copper gasket at the head. The new one just arrived. The side cover is back on, and I am anxious about if I did a clean enough job on the mating surfaces so as to not have a leak. I'd like to fill it with oil and fire it up for a few minutes to see if I have any leaks, but I'd rather not have to install the exhaust pipe and gasket just in case the worst happens and I have to pull the cover again.

Is it OK to run the motor without an exhaust pipe briefly? Or maybe I should just tack the pipe on without the gasket for now, and then put it together the right way if I pass the no leak test?

I did not use any gasket seal, only a light coat of oil on each surface, with a new gasket of course, but not an OEM Honda product.

 

[tomeben]

Can’t answer the no exhaust running question, but if it helps my right cover comes off fine without removing the exhaust - in case you want to put it back together and then start it.
(I’m convinced I’ll break a head stud removing my exhaust, so I’ve avoided it at all costs.)


Tom - 1982 CM450E

 

[mike in idaho]

One school of thought is, don't do it, because when the engine is shut down the hot exhaust valves will be warped by contact with the cooler outside air drifting into the port. The other school of thought is that it doesn't make any difference. Go to the track and you'll see some of the crew members make it a point to plug the open ends of the exhaust pipes, soon as they're shut down, and some of them don't. Personally, I would take ten minutes to install/remove the pipes.

 

[LongDistanceRider]

Once you fill the oil you'll know if there's a leak. Running the engine won't make a difference since there's no oil passages involved.
As a general rule you don't want to run any engine w/o an exhaust pipe due to potential valve warpage as mentioned by Mike. I know many people who do it but I will never do it.

 

[Randall]

I took the advice and installed the pipe. And happy to report no exhaust or crankcase leaks. However, I did have a valve cover gasket leak, since I adjusted the valves and used the same gasket because it looked good. It wasn't until I pulled it apart again and realized just how dried it had become. So, put it a new one, bugger is a challenge to get lined up and stay there. Once back together again I noticed a very slight little air leak in one of the corners. No oil was really escaping, more of just a tiny bubble keeping time with the engine. I'm hoping this will seal itself once it's been on there a while and the rubber heats up and molds to it better.

One thing I did notice when I was looking for exhaust leaks is the little holes in the mufflers next to the gaskets. At first I thought I had a leak, but then saw the holes. What are they for?

And wouldn't you know it, as soon as I put the last bolt back in, the skies opened up for our daily Florida pounding. Two weeks of work, and I'm ready to take it for a test spin. Oh well, maybe tomorrow.

 

[ancientdad]

I took the advice and installed the pipe. And happy to report no exhaust or crankcase leaks. However, I did have a valve cover gasket leak, since I adjusted the valves and used the same gasket because it looked good. It wasn't until I pulled it apart again and realized just how dried it had become. So, put it a new one, bugger is a challenge to get lined up and stay there. Once back together again I noticed a very slight little air leak in one of the corners. No oil was really escaping, more of just a tiny bubble keeping time with the engine. I'm hoping this will seal itself once it's been on there a while and the rubber heats up and molds to it better.

When you do a valve cover gasket on models with the shoulder bolts that hold the valve cover on, you should also replace the rubber grommets on the bolts too. They crush and get hard with age and therefore exert less pressure even on a brand new gasket, and they can leak oil around them if hard and crushed enough. And as I'm sure you've already noticed, the bolts are designed to only tighten up to the shoulder - so be cautious when tightening them or they'll snap off.

 

[Randall]

Interesting. I did replace one of the rubbers because it was missing a chunk. It was the side of the one I didn't replace that leaked. I will have to get another one at $12 a pop.

 

[LongDistanceRider]

The small drilled hole at the front bottom of the muffler is a water drain hole, exhaust systems collect condensation that will turn into water and rot the muffler from the inside.

 

[Maraakate]

When you do a valve cover gasket on models with the shoulder bolts that hold the valve cover on, you should also replace the rubber grommets on the bolts too. They crush and get hard with age and therefore exert less pressure even on a brand new gasket, and they can leak oil around them if hard and crushed enough. And as I'm sure you've already noticed, the bolts are designed to only tighten up to the shoulder - so be cautious when tightening them or they'll snap off.

First mistake I made with my CM400A about 12 years ago. I tried to do the right thing and use a torque wrench, but little did I know that it takes very little torque on those two bolts and it clicked immediately and I never heard the click. Just kept turning thinking "when is this gonna tell me its torqued?!" then I snapped it. Luckily my dad also worked in the shop for many years and had a friend who is all about the vintage bikes and drove out after work one evening and got it out in under 5 minutes with just a couple of pick tools.

But yeah, after that experience I have an older friend who is really into collecting Honda dreams. Told him what happened and he laughed and said for most of that stuff just doing "two fingers tight" is pretty close to where it needs to be. And sure enough, with those particular bolts he was right.

Live and learn. Gotta make some mistakes when you start out with it.