Maxim x valve train noise

Ok so I just picked up a 1985 750 maxim x, nice bike in good shape but has about 49000 kms on her. There is a vibration/ noise when the engine coming down on her rpm after you blip the throttle. I removed the famous radiatior guard that is famous for causing vibration but it seems to be coming from the valve train. Bike runs pretty good, number 4 cylinder takes longer to warm up than the rest. Iam thinking that she is in need of a valve clearence check for sure. anybody have any similar experiences or suggestions.

 

Do you have the stock pipes on the bike? If you do that pipe is a double wall and one can break loose inside the other, also check that all the pipe connections are tight as they can have a tendancy to vibrate at different RPM's.

 

Ok the pipes don't look too bad, but will have a look regardless. Never even thought about those!
What about the cam chain guide? Would a wore out guide produce the same vibration/noise?

 

A valve clearance check was due at 5000mi, so yea thats definitly the first thing to do

 

As for the #4 cylinder taking longer to warm up: might be a partial clog in the pilot circuit for that carb. If it hasn't been done lately, a good cleaning might be in order.

 

I would say that there hasn't been a lot done with the bike in a while. Carb cleaning is on the to do list as well. First up is an oil and filter change though, looks pretty black. I have been reading a bit on this forum about the crankcase seafoam treatment but I think I'm just going to go with the oil change. Not sure it's a good idea in these old engines.

 

Just a quick update, changed the oil and filter and pulled the plugs. Looks she is running rich as they all are pretty black. Also done a compression test with these results
#1-130psi
#2-90psi
#3-120psi
#4-120psi
So looks like and issue with #2 cylinder, probably the result of a tight valve, like I mentioned before don"t know when the last valve clearance check was completed. Also these results were with the throttles at idle as I forgot they need to be wide open, so will have to do again anyways.
Also the plugs are the resistor type (ngk dr8es-l) not the non resistor (ngk d8ea) that she calls calls for. Would this have a difference on how the bike would run?

 

New number with throttles wide open for the compression test
145,120,150,150.
So #2 is still lower than the other 3. So hopefully nothing major.

 

I'm very interested in your further findings. I have the same bike with the same symptoms.

 

I'm inclined to think that if you have resistor plug where there shouldn't be one, then your plugs won't fire correctly, thereby giving you your apparent rich condition. Correct plugs would be a good step.

Re: compression numbers. Valves shims needing attention will throw off your compression. But rings can as well. I think if you drop some oil down in the cylinder and do comp test, and if the numbers go up, then your rings are worn out and letting pressure leak by. If they stay same, then rings ok.

I'd be concerned about that low cylinder, if it were me.

 

I have to say the same as them however that does not fix your vavle train noise you hear. With the combo of low compression and noise I'm will to bet you have a way out vavle shim or a burn vavle. And That will give you a noise at all rpms. And a bad run

 

I haven't been doing a whole lot of riding lately, however I did install the correct plugs in her a while back. She is definatly running rich, and a valve clearence check is in order when time permits.
The bike runs good over all, no real serious bogging and can get up to speed no problem. the buzzing comes when the RPM is falling after you spike the thottle, no other time. Leaning towards valve clearences or a timing chain issue. Either way carbs are comming off for a cleaning and valve clearences are the next priority. I might even do another compression test and try the tablespoon of oil trick to see if the compression test results change. I recently bought a boroscope and will have a look inside the cylinders too. I'll keep you guys updated.

Mike

 

Mike, Just an FYI on the spark plugs, some of us have replaced the resistor plug boots with non-resistor boots + then went with resistor plugs.

other than that, how does she run? "getting up to speed" is one thing, but if she doesn't make you $hit your pants when you twist the throttle wide open, some maintenance is long overdue...

Gonna give you the standard reminder with any new bike here.... check your rear brake for delamination, + check your tire + brake hose date codes.

Also, there has been a rash of coil problems popping up recently. Check to see if your coils have any cracks in them and test to see if they are in spec... better yet, upgrade to Dyna Coils when the budget allows. I had some issues with a cylander taking longer to get up to temp that dissappeared with new coils. If you aren't going to upgrade the coils, make sure the booots have a good connection. (you might have really weak spark too)

also, DO YOUR VALVE SHIMS NOW, not when time permits - before you are asking about how to do an engine swap. The X has different shim check intervals, but you are WAY, WAY, WAY past that....

Also, your cams have to come off when you do the shims on the X, so you'll be able to rule out the cam chain/chain guards at the same time

 

Also, how's the carbs? a dirty pilot circuit can cause a slow warm up on a cyl too....

 

She is in need up a tune up for sure. I suspect the carbs are dirty as some cylinders warm up a little faster than the others and like i mentioned before the rich condition. I would like a coil upgrade too, when the budget allows. I have had a few rides on her but was kinda of hesitant to push her to much before I take a look at the issues at hand.
The fact that 1 cylinder is lower than the other 3 makes me think of more of a problem than just valve clearences. I would think that a overdue valve adjustment would result in less than ideal #'s across the board. Or has anyone expreienced otherwise?
Also how much pressure is normally in the crankcase at idle. Should it be noticable or not. (Say when taking the oil filling cap off) I'm thinking that if the crankcase vent is routed to the airbox, as it is, then there would be no pressure buildup.
This bike is new to me last summer and have no idea what was done with it in the past.

 

An out of spec valve will only affect the cylinder it "belongs to."

CHECK your valve clearances right away. Adjusting them takes a tad bit more effort than on the aircooled bikes, since you have to pull the cams. But CHECKING them is easy and it may give you a clue as to the low compression numbers on #2.