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Low RPM noise like piston slap, GL1500

5389 Views 10 Replies 10 Participants Last post by  CrystalPistol
Looked this problem up in search but found only items pertaining to 1200's...mine is a 1500.

recently added a 90 amp alternator on my 95 Aspy with 65k miles. about 20-30 miles after that I begin to have a noise like piston slap and a slightly reduced off the line acceleration (nothing bad, just a bit of reduced acceleration and just off the line). After about 1500 RPM everything is running and sounding just fine; great acceleration.
I went to the Honda dealer and had them take a look. They took the alternator off and still heard the noise. They said it might be the gear that drives the alternator, it might have worn out (after 20 miles?) and he has personally replaced about a dozen of these (at about $2000 estimated cost).
Been driving it for about 800 miles now, no big problems and I dont have the cash to have my mechanic go into the engine and troubleshoot (hell, a new engine is about $600).

Question is, has anyone else had this problem. Doubt it is the alternator, more like a coincidence that it began with the new alternator, but the noise is there. One mechanic explaned the noise as soundling like a "box of rocks"....but piston slap is probably closer to the sound.

Any ideas?
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First off on the alternator, did you replace the rubber isolators when you put it in?
Are you saying the noise was there when the dealer ran it without the alternator?

The box of rocks.... Does it only happen in 1st, N, 2nd, and 3rd, goes away in 4th and 5th gears? If so the 4th/5th gear shift fork may be worn. Goes away with revs up a little? This happens on a lot of pre 97 GL1500s, especially if there were floorboards attached with heel/toe shifter as many would ride with their foot on the shifter between shifts and that puts pressure on the forks in the transmission. Honda's fix was to put in a stronger fork and gears in the Valkyrie and 97-2000 GL1500. They warrantied some of these transmissions while the bikes were under warranty. I have a friend with a 92 that Honda replaced the transmission parts for that early on.(If it gets bad it starts popping out of 4th gear. Yes you can ride it for a long time just skipping 4th gear without problems to the transmission)
A test is to point the bike down hill in neutral and then uphill in neutral to see if the noise goes away.
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I installed a compu fire five years ago in mine plus new rubber dampers.It rattles a bit
until engine warms up, have no problems with the gears, 48000 miles then now 87000 miles.
I'd question what your Honda dealer told you. Alternator driven gear assy failure is known to happen occasionally on 1800's, but I don't think it's a known issue on a 1500. I've never come across it. Get a second opinion on that one.

Newday is right about those rubber dampers, when they get hard they can make a noise that is almost exactly like what you're describing. I'd try that first if they haven't been done.

I've also run into a situation on a 1500 with strikingly similar symptoms. Previously the customer had spent 3K on tran work at another Honda dealer, to fix the noise in question. When he picked his bike up it still made the noise...he was 'miffed' to say the least and when I got the bike he was in litigation with them. The noise ended up being the Compufire alt he had recently installed. I replaced it with the stock OE item and the noise was completely gone.
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The rubber dampeners are a common failure item. That would be my bet.
100% sure that the problem is the grade fuel you are using. Use the highest grade that is available in your area
100% sure that the problem is the grade fuel you are using. Use the highest grade that is available in your area
The 1500 is designed for low octane (87) fuel...
Thanks everyone (BTW, I like that avitar, Alex!). I am questioning the diagnosis by the dealership...these engines are pretty much bulletproof and I doubt anything developed in 25 miles of new alternator usage that would crater that internal gear. I am having the dampners replaced this week and will let you know. Oh...also, the mechanic at the dealer said the noise was still there when he removed the alternator, but much much less. Hoping it is a $16 set of rubber dampners.
had to put thin shims to back alt. away from engine noise stopped.
if his bike has the trigger wheel timing advance the higher octane might solve the noise problem, but im with Alex these bikes normaly run fine on the cheap stuff. my guess would be the rubber dampers, their cheap to replace.
Loose timing belts will slap at low rpms too, and if too tight they will sing. I installed new belts at 70 some odd thousand and they loosened up (or maybe I had them just a tad too loose) and they sounded like a little knock at idle ...
... so I adjusted tensioners again and then they sang some slightly ...
... so I adjusted tensioners yet again .... just right! ;)

I have a Comp-u-fire (actually two, picked up second off of a parted out wreck off ebay cheap enough as spare, looks near new). Mine has been in the '97 Trike since 1998 or 99 (except for a short time in 2005 when rotor developed a fault and I ran a spare stock alt for a few days) and I never have heard piston slap noise from it.
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