Troubleshooting an engine rattle

Are you sure bike is running on both cylinders ? You did say loss of power when rattle first occurred. To test, spray water or spit on exhaust where it exits the motor.

Could be a exhaust leak but it also sound like slapping. Maybe a piston? How many miles on it? Compression test? A poor mans test is to put your thumb over the hole and turn it over. If you can hold your finger over the hole, not run-able compression. Check both.

With the rattle I meant the very nasty overtones that only show when the engine is revved.

Today I decided to take a look at the carbs. They were pretty nice and clean inside. The vacuüm-membrane of the right cylinder however, has two small tears in it. I could imagine this caused the right cylinder to run somewhat leaner than the left one.
Preliminary conclusion is that the consecutive heat that is generated has either done damage to the valves of the right cylinder or possibly fucked up the piston. Close hearing (and mostly touching & feeling) the rattle also pointed towards the top-end. Time, therefore, to decapitate the engine and see what's what. This time i'll try to take some pictures --just for pictures-sake-

Wait a minute. Replace that diaphragm first. It controls the slide, needle and so on. It could be only that. One cylinder fighting the other one.
Steve

Replaced the vacuum diaphragms with new ones from a webshop called Woembi. Pretty nice quality, good instructions and affordable compared to OEM-ones that are virtually impossible to find.

The rattle is still there and seems more present this time. Also, under load the engine will not go past 3500 to 4000 rpm. I am getting increasingly puzzled. Seems like the head will still have to come off.

Can you do it in the frame? Take the valve cover off and look inside. My son had a GS 750 E. Instead of lifter cups, it had adjustable tappets . Two of them lost their lock nuts and fell off. It wasn't making alot of noise because it had two valves instead of one but power was down. I fished them out with a magnet (my son was too lazy) and put them back in. It happened again so this time I told him to find them and we would use lock tight. He opened it up and walked away after a few minutes. He was given a Honda 350 so it was party time and he left home, got a DUI, lost the bike and moved to LA. I kept his Susie for 10 years. He called wanting to get his bike running again. I told him to hop on a Grey Hound and fix it. He said he didn't have the money for a bus ticket. Mean while my Z1 is sitting waiting for me to scrounge up the money to put her on the road. Couldn't help him. I mean WOULDN'T help him. All it was is the tappets but after 10 years, it needed more than it was worth. I scrapped it. Too bad. The front end alone would have been a good up grade for my Z1.
I hope your problem is just as simple. Most of the time it is.
Good luck and keep me posted.
Steve

Decapitated the block as promised. Since the vacuum membranes did not absolve the problem it just had to come off. One of the valves (exhaust, left cillinder) has a white discoloration that indicates overheating. Also there seems to be a fat amount of carbon deposits (granules) in the head. The 'zuigers' (Dutch for pistons, literally translates to 'suckers') look fairly OK. Even and black carbon deposits.

All valves will rotate, indicating none of them is really bent. I will check the seats later, when my housmate returns with a valve-spring-compressor-thingie that he currently needs to refurbish his '50s Triumph-21




Just for the fuck of it, a little backyard testing of a seriously tuned puch mv50. To keep the spirits high I suppose.

Fill the head bowels with gas and see how fast it runs out. They look normal. The carbon indicates a poor state of tune. How do the cylinders look. Any marks or scratches? The cam chain may have skipped a tooth or the adjuster is shot. Looks like one piston is higher than the other. Turn the crank back and forth a little to see if there is any slop. If so, bad rod or wrist pin. GOD I hope not.
Good luck

Took the discoloured exhaust valve out yesterday. The seat and valve are very modestly grimed and pitted by carbon buildup, but the valve itself was completely straight. Since i've got the head of anyways i'm planning on just re-seating all four valves with a bit of polishing paste. I'll also review the cillinders under close scrutiny. Any way to check the integrity of the piston rings without taking the cillinder off? I suppose i ĺl just be looking for marks inside the cillinder walls eh?

Janklaassen wrote: ...Valves were just fine, no leaks and good compression. ....

Janklaassen wrote: ...Any way to check the integrity of the piston rings without taking the cillinder off? I suppose i ĺl just be looking for marks inside the cillinder walls eh?

That's one of the reasons for the earlier recommended leak-down test.

But, good compression generally indicates that pistons rings are doing okay, and that valves are sealing okay (at least when the engine is relatively cool).

Was the compression test repeated with a teaspoon of oil added inside each cylinder?

Good Fortune!

Did the head rebuild. All four valves have been re-lapped with grinding paste, all involved parts cleaned as well as i could. New oil-seals were used and new exhaust and head-gasket. Did a last leak test by filling the combustion chambers with high-flashpoint solvent. Over the course of several hours they proved leak-free. The reassembly was done according to the manual. Valve clearences were obviously readjusted.
Note; Old spark plugs in there for the leak test,


However, the noise is still there and i'm steadily running out of options. Starter clutch catching perhaps? Counterbalancer? Something is wrong and I'm not able to rest before I find it.

Janklaassen wrote:
However, the noise is still there and i'm steadily running out of options. Starter clutch catching perhaps? Counterbalancer? Something is wrong and I'm not able to rest before I find it.

A few years back, my bike developed a persistent vibration above 3500 rpm. I finally started tapping on the (stock) exhaust, thinking the baffle was loose or something. It wound up that down-pipe #4 inner pipe was just loose enough to touch the outer pipe at certain rpms. No option but to replace the exhaust, so I went with the V&H street pipe...problem better-than solved.