rattling noise in engine driving me crazy!!

[Fabz]

Hi
I've recently just joined and Im loving the website so far! I'm a recent proud owner of a '88 RDO2 dominator and having bought the bike in an 'as is' condition, im fixing minor problems that the bike had when I got it. Ive had it for 2 months now and I've managed to get rid of all the problems it had except for one---the loud rattling noise that comes from the engine. I must say its driving me nuts... I've changed the timing belt, valves are on point...I don't know what else to look at. The bike's performance isn't affected, but the noise is extremely irritating.
Help anyone...

Fabz

[bazzyj]

hi
have the same problem, only when cold, new piston and rebore all ok but noise still there,thought it was piston slap sounds like loose tappet but seem ok valves checked and springs ok but you cannot detect from where?suspect decompressor rattling can anyone else help. noise does decrease slightly when warm but stil sounds like tappet, timing chain and tens all ok.
bike runs perfect no running issues what so ever

[Fabz]

hi there
i was beginning to think i was the only one with this problem cause there were no replies,...so thanks for replying. i too thought it could be tappets, but the guy i bought it from reassured me that he had replaced the old ones with brand new ones (showed me the old ones) and so i did not bother to check....would they make that much noise if they're loose?...mine too gets a bit quieter when bike gets warmer but not alot ,...noise seems to also decrease in between gear changes while accelerator is idle, but picks up again when accelerating...someone suggested to check the camshaft... but i don't know if a worn out camshaft would make that much noise,...and plus it would definately affect performance no? anyone got other helpful tips?

[bazzyj]

Hi
think ive got to the bottom of this issue. The noise is hard to detect even though it is quite noisey, if you put screw driver to your ear and scan around engine you cannot pin point it.
took cam cover off the weekend and cam shaft is fine also tappets etc, however there is alot of slack in decompressor unit, although works fine this is causing the rattle when cold and will increase with engine revs, when hot this will expand making it quieter.
I would imagine you can get this seperate from the camshaft, as manual shows dissassembly.
Anybody out there changed this component?? if so is this going to be genuine part or can you get pattern part??

Bazzyj

[Scott]

....there is alot of slack in decompressor unit,

Excuse my ignorance and apologies for this not really helping but what does it do?

[bazzyj]

Hi
due to the high compression ratio on this engine, when cold or first starting it would be difficult for engine to turn over. the decompressor works on the exhaust valve, when initially turning the engine over this decompressor will hold the valve down longer so compression is slightly lower for engine to turn over, once the engine has fired this decompressor is no longer needed until the engine needs restarting.
Earlier bikes had and additional lever on the handle bars connecting to a cable. my bike has an automatic one 1996 model ie low engine revs decompressor activates until engine fires

Bazzyj

[Rubberchicken]

The dommies have always had the automatic decompressor.
I think the XR or XL had a manual lever on a 5th valve for some time, but not the dommie.

[Fabz]

hello again
so the decompressor's the problem? unfortunatley i can't check mine right away because my bike is at a body shop getting a makeover, but i should get it in a couple of days and i shall definitely check it out. incidentally, you said that earlier bikes had and additional lever---do you know which ones exactly, and how did the lever work? sorry if i sound dumb...

[bazzyj]

Hi
lever did the same thing, open the exhaust valve until engine fired,what they call valve overlap
let me know how you got on

[Scott]

aaaaaah. I see. Thanks