Logo
FULL SITE MENU

BF25A Cam Pulley Failure

J

Joelomunro

New member
Gday from Australia,

I have a late 90s BF25A which I picked up a couple of years ago as a project engine knowing that it'd got water into the oil. Pulling the head revealed that there was corrosion through into the water jacket behind #3 exhaust valve. I eventually tracked down a second hand head in good condition, clearly a fresh water only engine, and proceeded to swap it over onto my engine. The replacement head didn't come with a cam pulley, so I swapped mine over from the original head. I'd had the engine running in a drum a few times, but only able to run at a high idle at most and out of gear. I recently finished off the boat that the engine was intended for and proceeded to wet test the engine and boat.
About 15 mins into running and just poking along at about 2500rpm the engine abruptly stalled and would not restart. I lifted the cowling and noticed that the cam pulley was oscillating and out of whack. I got back to the boat ramp with my trolling motor and headed home. When I removed the pulley I found that the keyway had broken out of the cam and the cam pulley locating pin had come adrift and was jammed between the top of the cam shaft and pulley. I had a spare cam from the original head and I sourced another pulley from a wrecker which I assembled a few days ago. The engine fired up easily in the test drum again and seemed to run fine at idle, so I went to give it another wet test again today. I had pretty much a carbon copy run of the other week and the cam and pulley have failed again. I made sure to torque the cam bolt up to the specified 27nm and re checked it prior to heading off to run the engine today, yet it still seems to have loosened enough to lead to failure.
So what am I doing wrong, and how do I prevent this from happening again, as chasing up parts for this engine is now starting to get uneconomical and pretty disheartening.

Thanks for reading and I'm early looking forward to the wisdom of the forum.


Cheers

Joel
 
Hi,
Very strange Indeed!

I wish I had a good answer for you but I don't.

I initially thought that maybe the crankshaft might have too much thrust, causing the timing belt to change angle, putting an:"angular bind" on the camshaft. But I'm not sure how that would cause this to happen and cause the pulley bolt to loosen.

I did find something odd though when I looked at the parts page for the thrust washers for the late 1990's 25A models
There's no quantity given.
That made think that the crankshaft for those might be different from the later models but the parts numbers are the same.

1998 model, see item 10. There's a price listed as if available but quantity is 0


Here's 1999: Again, no quantity.
This could simply be a typo mistake but keep it in mind when shopping parts.


Year 2000 was the same, 0 quantity



And Here's 2001....quantity 2.



You might still want to check crankshaft thrust since it's an older engine. I don't have the specification but I would be concerned if it were greater than 0.010".

My other thoughts about this is that I have found the crankshaft retainer nut completely loose on a couple of Honda twins. I was able to simply replace and re-torque those but I think I caught them early. The reason I popped the flywheel was I heard.a "ring-a-ding-a-ding" sound when the engine was idling. The sound was caused by the loose nut and.retaining washer bouncing around. In the link below see.items 15 and 3 as as example:


I do remember seeing at least one cracked cam pulley although, again, on a twin. BF8D I think it was. So, they do fail. Maybe you just got unlucky. But something breaking twice like that makes me suspicious.

If you don't find a "smoking gun" reason and you try replacing it again, maybe use some Loc-Tite and 3 or 4nm additional torque. Adding torque when using thread locker is recommended because it's not a lubricant and causes slight friction.

I will be very interested if you can find why this is happening so I'm standing by awaiting your post about the solution.

Good luck.
 
I've sourced a spare parts engine which I'll pull the cam and pulley out of and have another try at it. I think you're right in that I'll use some red loctite and a little more bolt tension and hopefully have a with with it.

Joel
 
Well in stripping down the parts engine today I think I've identified my stuff up with the previous cam and pulley.

When I originally bought the engine and pulled the head to track down whether it was corrosion or a head gasket causing the water in the oil I had taken the head to a local head reconditioning business who stripped it completely before giving the ports a light sand blast to clean up and finding corrosion through between the exhaust port and the water jacket, rendering the head pretty much un repairable. I got the head back and a bag of bits and pieces, so I didn't have an assembled head for reference when I was fitting up the replacement.

Fast forward a few months and I had the replacement head in hand, less cam pulley, fuel pump and crucially for this part of the story, the oil gallery cover plate which pressurises the oil feed to the top cam bearing. Without having the original head assembled for reference, and no photos on hand at the time, I swapped over the parts that I needed and assembled the head on the engine, without the oil gallery cover. I believe that the cam nipped up just enough to break the drive pin and pulley without completely seizing the cam in its bearing surfaces. I noticed the cover plate straight away when stripping down the parts engine today. There is a small amount of marring of the bearing surface, so I am going to run a three stone hone in it to give it a bit of a clean up and then swap over the salvaged cam and pulley from the parts motor, and keep my fingers crossed.


Cheers

Joel
 
Wow! Yeah, that would probably BITE most of us with no previous knowledge or experience with these.
I agree that you've probably isolated the cause for failure. I hope your fix works out.

As an aside about your previous plan for using red Loc-Tite...
...many think the red is sort of permanent. I used to also. But, after attending a very extensive Permatex product training class, they informed us that the red simply has more sheer strength and will release with the same heat applied as would the blue compound.

Good luck.
 
Back
Top