Hi, I have a 1980 80" shovelhead..

So I recently finished my chopper project, I had it running well on points for about ten days. It fell out of timing, because the two bolts that hold the timing in place lossened up. So I reset the timing and, and adjusted it accordingly with a timing light. The day I did this I started to get a loud hollow pinging noise coming out of just the rear exhaust pipe.

It has been like this now for about a month.. It sounds to me like a detonation in the rear exhaust pipe, like there is too much fuel? I only happens once the engine is warmed up, then it does not go away. The sound also only happens when you let off the throttle, you can hear it a little when idling, but you really hear it when you let off. I does not happen when giving it throttle. and does not noticibly effect preformance, though it sounds like hell when you let off it.


I first started to fix this problem be adjusting the super e carb. (didn't change the sound)

-then I thought it might be the rear exhaust vavle not seating properly, so I took off the rear head to check the seats, and vavles, everything checked out , so I reassmbled the head (a no go on the fix)

-then I thought maybe it was caused by a collapsed lifter, so after changing two, with no avail, I switched to solid lifters. (no fix the sound is still there)

-so with that out of the way a assumed it was the timing and tried adjusting the points, advancing and retarding the timing, I thought that advancing it would take the sound away, and for a moment I thought it did, but in this setting I could not get the bike to start, so I returned it to my original timing mark, and was able to start the bike, with the noise!

-at this time I was convinced it was the timing so I switched to a power arc electric ignition, single fire, multi-spark. (didn't fix the noise)

-Then i though maybe it was the carb. so I switched to anyother super E carb. (no go still making the noise)

-Then I though maybe the cam? so I removed the Andrews f grid and installed a stock harley cam, this did nothing for the noise and might have made it worse, though it is hard to tell.

I am at whits end I do not know where to go from here?

- about the engine,

1980 80" Shovelhead
currently running
-Power arc single fire, multi spark ignition
-solid lifters
-stock cam
-super e carb
-60w oil
-vavles have been machined to allow andrews f grid cam
-i run 93 octane plus octane boost sometimes.


Any Help or insight would be awesome

Thank you so much sorry for all the writing but i figure the more you know the better.

Thank you, Sean

I have had a lot of people with a lot of expierence in on this problem not only have they no idea what is causeing this noise, they have never heard this noise.

again, it sounds like it is to far retard almost (but it is timed perfectly to true top dead center) it is a hollow pinging sound coming from the rear cyclinder exhaust, almost sounds like there is way to much fuel going there and igniting in the exhaust when hot ( i have also changed the pipes to see if that would work)

Thanks Sean

 

sorry for the grammar issues i typed this super fast, because i have an appoinmetn waiting on me, haha ok thank you

 

Although you didn't mention it, I'll assume after doing everything you did that you checked your push rods for straightness and adjusted, and checked your valve springs.

Does seem suspicious that it started the noise right after you adjusted the timing. Hmmm.

How about your rear pipe gasket?

 

question -- does the noize happen while driving at say 30MPH in third with light throttle

i have had that noize before -- jz

 

Hi, thanks for the answers, the push rods are straight and new, I switched to solids to see if they would effect the noise, I also check them every time I go to adjust the timing to make sure they are good. I have put two different rear pipes on the bike to see if it was just the pipe or gasket, but I still have the noise no matter which exhaust I run or how many gaskets I put on the pipe. (i hate the single bolt design lol)

The nois happens no matter what speed I am at, but only occurs when you release the throttle.

It is like it is creating a vacuum leek, but there is no leek, I changed the carb to see if it was that, but no luck.

I tried a stock cam, and feel like it made it worse? not sure though, now I might just be imagining that?

I am going to manually advance the timing and see if that works...

 

Also the springs and valves are good I have had the heads apart a few time to check this, since it seems to be a valve noise

 

does the mechanical advance work?

 

Joe12rk, with the style of electric ignition that I have there is no mechanical advance. I am going to try and set the timing based off the advanced timing mark on the flywheel, instead of TDC to see if that helps at all.

 

i am not in an ears shot of this BUT i have had that same issue and it turned out to be the connecting rod bearing roller and or the crank pin had failed --

the 3 i have seen have been the hardness had gone away in the crankpin rear rod area all on one side, and this caused the pin to chew up and start to make odd to say the least noises

 

Johnjzjz, Thank you for the insight, I have a funny feeling it might have something to do with what you have said. When I put everything back together and fired it up I left the cam timing cover off and notice the timing wheel was not rotating in a perfect circle, but rather an oblong pattern, leading me to believe that the bearing either on the inside of the cam, or the brass fitting in the cam cover are shot. This conclusion I just came to. I have been looking over all the details, and come to think of it the other day I did notice that some of the bolt heads holding the cam cover (the cone) where bent at the head. I did drop the bike on the cone side, but honestly did not think it was hard enough to cause damage, just a slip of the foot, due to a clutch that wouldn't disengage, (a whole other issue) and a quick grab of the front break in gravel, and down she went faster then I could react. But I did not think this would cause the issues I am having! but it is worth changing the two bearings to find out.

Hopefully it is just the brass bushing in the cam case!

I will keep you all posted.

thank you

Sean