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Oil Leak? Please help

82HAWK450T

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Jun 3, 2022
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Saskatoon
Hello everyone! Seem to be having a bit of a leak issue on my CB450T Hawk. Not sure if this is common or not but looking for some friends to help identify where the issue might be. Seems to be coming from every where in all honesty, first i figured a seal was likely pooched now i'm wondering if i don't have a crack somewhere. Any insight at all for this beginner would be extremely helpful!

1982 CB450T engine 1.jpg1982 CB450T engine 2.jpg1982 CB450T engine 3.jpg1982 CB450T engine 3 (1).jpg
 
My first impression is that a gasket is leaking, possibly the head gasket. Is it running okay and have you checked the compression since buying the bike?
 
Our resident expert on this model is out sick for a few days and I know virtually nothing about the SOHC 400/450 models, but I can tell you from experience with this type of valve cover gasket and bolt seals that it could be where the oil is coming from. When you adjust the valves you can replace the gasket and the rubber, chrome capped seals that go over the bolts that hold the cover on. DO NOT try to tighten the valve cover bolts to slow the leak down, you will break them off because they have a shoulder and cannot be tightened beyond when they bottom in the head. The rubber bolt seals get squashed and the pressure they exert on the valve cover diminishes with time so between the old gasket and the bolt seals getting squashed and hard with age, they usually seep oil from there.
 
Start by thoroughly cleaning the area. Then spray it with talcum powder. Then run it. You should then be able to see where the leak (s) originate. Pictures 2 and 4 seem to support Tom's theory.
 
My first impression is that a gasket is leaking, possibly the head gasket. Is it running okay and have you checked the compression since buying the bike?

Just actually got a compression kit so i was able to check it this morning. on the cylinder it was right around 90psi and the other is right around 110psi. I'm guessing thats a bit low for both.

1982 CB450T CT 1.jpg1982 CB450T CT 2.jpg
 
Just actually got a compression kit so i was able to check it this morning. on the cylinder it was right around 90psi and the other is right around 110psi. I'm guessing thats a bit low for both.

Did you turn it over until the gauge stopped rising? Warm, with the throttle wide open? Those numbers are definitely low for an engine that at least runs. Long hose effectively lowers the reading as well. BTW, a head gasket leaking oil generally does not mean compression loss, they're separate section of the gasket not close enough to be affected by each other unless extreme circumstances and then it is unlikely the engine would run at all on that cylinder
 
Just actually got a compression kit so i was able to check it this morning. on the cylinder it was right around 90psi and the other is right around 110psi. I'm guessing thats a bit low for both.

Those would be very low. When you got those numbers, were you holding the throttle wide open? If not, please try it again holding the throttle open and see what you get. I don't know the exact numbers for the 450T, but I think below 150 or so would probably suggest a rebuild is in order.

Based on your plan to do a custom build, it will likely be worth your time to go through the motor now, rather than take it apart later.
 
I did not have the throttle open on the first attempt. silly really because of all the reading and watching i've done said to do just that. Redid the test and both cylinders were right around 120. Engine warm and throttle wide open.
 
Well, then it should run but won't be all that strong. Still, nothing to do with the oil leak
 
Well, then it should run but won't be all that strong. Still, nothing to do with the oil leak

It may not explain the leak, but does establish probable cause to enter the top end and hopefully kill multiple birds with one stone by replacing all the gaskets during the rebuild.
 
It may not explain the leak, but does establish probable cause to enter the top end and hopefully kill multiple birds with one stone by replacing all the gaskets during the rebuild.

No doubt, just figured he might work out other stuff like carbs or rideability before digging into the engine.
 
From one of the pictures I can see a large leak from the valve cover gasket. New gasket and both valve cover bolt grommets are needed. From there it's power wash the engine, run it and see if there's any more, probably not. If there are then the baby powder routing is in order.
Since it starts and runs I'm guessing that the compression readings are wrong. 135 is the lowest I've seen and still, with difficulty, get one to start.
 
I will say this much, every old Honda I've had it leaks somewhere from the valve covers or head gaskets. Never enough to really make it a big deal, but you see some of what you're going on. I just check the level once a week, never really big enough to need topped off and just drive on.

Years ago, my dad and I tried replacing the gaskets with an Athena kit on the CM400A and it worked great for a week but then started leaking again. We realized afterwards that we didn't swap out the o-rings in there too, so that's probably part of the issue. It was such a pain to get the exhaust off, even with a torch, and the leak isn't that large that I've just lived with it. If it gets so bad that I'm dumping a quart in every week then I'll deal with it.

I know that's not the best advice, but doing the gaskets can be quite a bit of work if you haven't done it before, and it's very easy to do it wrong. We thought we were paying good attention when we did it and we still missed something.

I also think you're supposed to replace the cylinder studs when you do it, which we did not and I don't think they are easily sourceable at a price for the people (or they weren't when I looked previously). I think you can get away with reusing them once, maybe twice, but after that they are junk. Is this correct?

So to recap, I say if it's a relatively minor leak that's kind of staining the fins, not eating up a ton of oil and not ready to start a fire I'd just live with it, personally. But, I understand if you want to fix it now.
 
I've found that so many of the compression testers don't read the same. It's really more about making sure the PSI is pretty equal across all cylinders. If they're relatively equal and the bike runs OK then it's probably within spec. You could do a leak down test as well.
 
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