My recent adoption is a little down on power -- suggestions?

So, got my "new" XJ750N home. Have spent a little more time with it and getting in tune with how it sounds.

I'm pretty convinced the bike is down on power from where it should be. I haven't been to the redline more than once or twice but I'm not feeling the rush I expected over 6k. In general in low gears it accelerates smartly under medium throttle but doesn't seem to have much left when you crack it wide open, it's almost as if the throttle isn't actuating bey0nd 3/4 or so (although I don't actually suspect it's a throttle problem; that's just kind of how it acts) Also doesn't quite have the torque at low rpm that I would expect. My previous experience was on a XJ650 so I'm relating it to that. It sounds good when you rev it and when you take off in the first few gears but I just know it should have a lot more punch than this.

I replaced the outer plugs, gaps and burn patterns looked perfect. Inners to come this week (needed some tools). Supposedly had a carb job done about 5k ago. Air filter is pretty bad, I blew it out for now, new one being installed shortly.

I'm thinking next I need to get inside and check out the timing chain -- sounds a little loose to me. Perhaps also check the valves. Anyone else go some thoughts as to what the best sequence of things is to check?

Otherwise it's surprising how many little things have been let go... clutch cable was binding, needs replacing, did rear brakes, brake switch is nearly shot, speedo drive is fried, front wheel bearings were toast, a couple minor electrical issues, exhaust cracked from over-tightening of incorrect clamps... surely will find more as we go along.

Still very happy to be aboard a Maxim again!

 

The best sequence of events is to assume that everything is Effed up and go from there. Begin with checking valve clearances and work your way through the maintainane scheule until every moving part of the machine has been inspected and put into correct working order.

 

That's definitely the plan over the winter. I would like to get a few months of light recreational riding in meanwhile. I was going to assess the primary chain and probably do the valves in the next week or two, but anything more involved inside the motor would probably wait for the winter when we will be splitting the cases and having a really good run at everything.

 

just curious, what year is the bike? as k-moe said, you should first start by checking the valve clearance, once they are in spec, among other things, you should read this http://www.xjbikes.com/forums/threads/in-the-church-of-clean.14692/#post-120723 only because you said this ..... Supposedly had a carb job done about 5k ago

and then read

http://www.xjbikes.com/forums/threads/the-information-overload-hour.27544/#post-233801 which is under k-moe signature,

speaking of signatures, please go to the top of this page and where you see your name, select your name, and then select signature and put in your bike type, that way we all know what bike you have..... and I just gotta say....when I read this "I haven't been to the redline more than once or twice" ......... I thought to myself, holy smokes I hope this bike is spot on........... asphalt is not very forgiving..... just sayin

 

Many a Maxim X has expired due to a tight valve ! Due to its shim under bucket many have not been done when needed I'm doing a valve adjust in one right now and 8 of the 20 valves way under spec. Most bikes that have been well maintained will not need that many shims and not 2sizes too tight! Most new bike dealers will not work on bikes that old. ( $300+ dollar service on a $1500 bike scares people away and something always breaks) How many miles or in Canada kilometres on it ?And a dirty air filter will cause poor power in the high gears and revs.

 

Read it previously, superb document. If we decide the carbs aren't in appropriate shape, my father will be doing the carb rebuild over the winter, it's well beyond my skills. I've never messed with carbs, I always hand that off to him, he's a wizard at that.

Done, and thanks. 85XJ750N for future reference and in case the sig doesn't show yet.

I'm not sure I took my life in my hands particularly by going for the redline in first gear once or twice just to see how things sounded and how the powerband felt in a bike that was a daily driver for somebody else as of December. I was trying to express that I don't do that routinely and would add that I wasn't doing any top speed runs or anything. Clear smooth country road, riding alone, paying attention to the sound and feel. Otherwise it's just been some easy cruising around town.

I think we will go ahead and check the valves before we go much further. The air filter will be going in along with the speedo drive, brake light switch, clutch cable and a few other parts that should arrive at my dealer shortly.

The bike has 60, 000 miles on it. It's cosmetics are in great shape so it has definitely lived indoors and overall seems not bad although the PO wasn't as good an electrician as he fancied himself. Working through that.

I will say this, having spent a lot of time working on 20 year old (4-wheeled) BMWs in the 200k + mile range, the bike seems to have stood up extremely well and the parts are very well engineered. Surprisingly so really.

-iX.

 

An update on this... we have the top end opened up and are checking the valves. We have feelers for .04 and .08 (upper and lower range per manual on intake side) but I was hoping to set them more exactly than that -- bought a set that had .05 .06 .07 etc but they are too wide to fit for measurement.

Should I grind down those ones to fit or is just being somewhere between .04 and .08 close enough? How fine are the differences between the actual shims?

Also is it worth waiting a week for a correct purpose-built shim bucket depression tool, or should we just use a screwdriver like the local bike shop guy does?

Side note... oil pump chain seems a little on the slack side, but nowhere near enough to take out a link. Ok as is? No adjustment or tensioner that I can see.

-iX.

 

1. You cannot precision grind feeler gauges at home unless you have a grinding post on your lathe, or milling machine (I will assume that you have none of those machines), or years of experience with precision grinding/lapping by hand. And even then you have to take into account the precision polishing that has to be done following grinding. In short, no. It wound'tn be worth the trouble anyway because...

2. You can stack thinner feeler gauges to measure the sizes that fall between the larger feeler gauges.

3. There are misprints in the manual. The proper clearances can be found under the left sidecover.
Intake: 0.11 - 0.15mm ( = 0.004 - 0.006")
Exhaust: 0.16 - 0.20mm (= 0.006 - 0.008")

4. Using a set of Metric feeler gauges is easier. KD tools 2274 or another manufacturer's equivalent is a good set (note that these are not SAE gauges stamped with the metric equivalent, but true metric gauges).

5. The shims come in 0.05 mm increments. In spec is in spec, and out of spec is out of spec. You do not need to measure beyond the 0.05mm increments. This will become clear as you study the shim chart in your service manual (the table is correct and has no misprints).

6. Use a length of wire as described in: http://www.xjbikes.com/forums/posts/122016/
Using a screwdrive to hold the buckets down invites damage to the bucket, or the cam lobe. I would not return to that shop to have any work done.

7. The oil pump chain will be somewhat slack. There is a inspection procedure in the shop manual for checking chain length and the pump shaft runout/ slop. The only remedy for an out of spec condition is replacing the individual parts.

 

Thank you sensei for the very informative post especially with regards to the misprint -- this is for the 20 valve head though, right?

Just to clarify I was going to grind the side of my feelers so that they are not as wide, using a belt sander most likely. Done correctly it should not affect thickness or measurement. They are currently too wide (tapering from a point that is fine to a body that is to wide) to get deep enough to take a measurement on anything but the outermost valve because they hit adjacent hardware when you try to insert them.

This new set I just bought yesterday has many very fine measures, in some cases listing sizes to .xxx5" I imagine to ensure that a particular metric measurement is hit. However as mentioned they are too wide. In any case they have .004, .005, .006, .007 sizes I can use so we should be good from an accuracy point of view.

With regards to the cam chain guide -- it's intact, but currently exposed, so I thought to replace it anyway. Dealer says discontinued and can't get. Any way to assess condition or is it just foolish to even consider not replacing it while everything is open?

 

Maybe I misquoted, because this is from Len's catalog:

NOTE: all XJ700-X and XJ750-X models use the following valve adjusting pad clearances:

Valve Clearance Intake: 0.11 - 0.20mm (= 0.004" - 0.008")
Valve Clearance Exhaust: 0.21 - 0.30mm (= 0.008” - 0.012")

The earlier specs come from the Maxim-X valve adjustment how-to thread.

I suppose that careful grinding of the sides of the feelers would work. I would use a whetstone to to the job so the edges of the gauges don't get a burr on them.

Len (Chacal) has these:
HCP6383 Aftermarket METRIC FEELER GAUGES SET. These gauges will work on all XJ engines including the XJ700-X and XJ750-X water-cooled models, which require narrower blade-tip feeler gauges to check the intake valve clearances on those models. Aftermarket 32-blade metric set has 95mm long blades, hardened and polished, with the thin, tapered ends needed to access the valves on these models. Marked in both metric and decimal equivalents, as listed below. NOTE: these feeler gauges will fit perfectly, although you will have to rotate the blade 90 degrees to the holder for some of the inner valves on X-models. Each:
$ 14.95


I don't know what your dealer is looking at, but the parts lookup fische shows the primary chain upper guide is still avaliable. He may be thinking of the XJ1100 guide.
One source (Chacal being another) http://www.yamahapartshouse.com/oemparts/a/yam/500426c3f8700209bc7886fb/starter

Replace it, and be very careful when removing the retaining bolts as they can snap off.

 

Are we sure this bike is an X model? I know that you've noted that it's an XJ750N but I don't think there was an air-cooled version of the 1985 XJ750 model......only the XJ750-XN (water-cooled) model. You mention inquiring about the shim-bucket hold down tool, that is only used on the air-cooled models. Does the bike have a big honkin' water radiator hung way out front?

Have you taken the oil pan off (or the engine apart)? Otherwise, you cannot see the oil pump chain. With the valvecover off, you can see the CAMSHAFT DRIVE CHAIN, and it will have a tiny bit of slack in it (but not much). The automatic chain tensioner should take up any slack, if it is working properly.

 

Hi k-moe, just got back from working on it a bit more. We trimmed the gauges down so they fit fine, everything seems to be within spec no shims needed. Kinda disappointed as I was hoping to pinpoint that as the source of the missing power. We had the upper chain guide off, it looks really good, perhaps it has been replaced already. The chain also looks perfect with no detectable wear. I think we will probably leave it in place and button everything back up with a new gasket. We did replace the plugs, center two looked pretty old and gross although the gaps and burn patterns were good all across, and noted the air filter was dirty, but didn't find anything else to blame. If I'm still down after we fire up again I'll go at the carbs I guess.

BTW The updated specs you just gave agree with the factory manual that we have on hand. I had one intake at .004 and one exhaust at .008, but everything else was in between the specs.

20 valves and a radiator. Yup it's an X. In Canada we have both the water cooled (-X) and air cooled (non-X) models in 750cc for 1985. However I may have quoted the wrong model number for my bike, excuse my noobiness. I amend my notation to XJ750XN. As far as the tool, I was reading air-cooled information (and drawing on previous shim-bucket motors including my old XJ656) and getting mixed up, I know the difference now that I have been in there properly. I'm learning, bear with me.

The slack I observed was in the oil pump chain not the cam drive chain. I observed the oil pump chain after removing the clutch. Although we did later pull the oil pan to check for debris from a washer that had disintegrated inside the forward section of the final drive. More on that to come in a new thread. Oh, by the way to that end, what is the proper name of the shaft that extends from the clutch housing over to the driveshaft, anyone know?

 

The middle drive gear.

 

Ok.

Anybody ever had the middle drive gear nut come off and remain trapped in the approximately correct location for an unknown number of miles before being discovered?

 

We may be talking about different things. THe only nut on the middle gear (#3 in the link) is on the opposite side of the engine from the clutch http://www.yamahapartshouse.com/oemparts/a/yam/500426c4f8700209bc7886ff/middle-drive-gear
Give us a picture of what you see.

 

#3 in that diagram. We hypothesize it was installed incorrectly and came loose. #9 became shrapnel. Some additional calamity ensured, however, the bike continued to function.

I will give pictures when I get them all assembled.

 

Oh boy. I would bet that the locking washer was not put on, or put on incorrectly at some point (doubtful it was at the factory, but things happen). Hopefully there was no truly expensive damage done.

 

Well put it this way, I think it's good we caught it when we did. The shaft had play as a result of the "missing" nut, however it's captive so it continued to do it's job in the drivetrain. While doing so though, it neatly machined a mm or so off of half of each of the rivets on the back of the clutch pack. I have no fear for the integrity of the rivets as discovered, but if the process had continued eventually disaster would have resulted as the clutch pack would have come apart.

As it is we retrieved lock washer shrapnel from a neat little recess in the case around the final drive head and ordered a new one with it's attendant nut.

Having had the entire clutch pack out and apart as well as the final drive and the oil pan, I'm content that there are no other loose bits and also content that there is no damage of consequence to anything. Which is a dang miracle, I'd say.

So at this point we've done pretty much everything except split the cases as far as the drivetrain goes. other than the carbs that is. Clutch is perfect, all gears and chains look great, all bearings are great except the front wheel which we replaced.

 

Oh. we are talking about different parts. Sounds like your clutch basket nut came loose.

 

It's part #3 in the diagram you referenced that came loose. The damage to the clutch basket came from the other end of the shaft. With the nut missing, the shaft had horizontal play and the clutch side end of it was contacting the riveted side of the clutch basket as it spun. The driveshaft side end succeeded in carving a neat curve into the nut where the thread used to be but that's all. Luckily the teeth at all ends and intersecting gears are all perfect, no damage at all. So we got away with it.

Good thing we went in there -- there was no functional reason to do so, everything was working fine, but we noticed a noise that I originally feared was a loose chain but we traced down to that location.

-iX

 

By the way here's an update for ya -- the intake valves are fine, but ALL the exhaust valves were in spec for the NON-X head, ie .006-.008. So I misspoke earlier when I said we were in spec, I was lulled by having glanced at the chart in my old XJ650 manual *and* the fact that all the valves agreed. So we are hypothesizing that somebody did the valves, perhaps recently, with the wrong manual in hand.

So my question for you, sensei, is what is the net effect of all the exhaust valves being too tight?

-iX.

 

They will not open as much ash they should, impeding exhaust flow and potentially burning the valves. It takes a fair amount of time to burn a valve, so you should be fine with just readjusting them.

 

Thanks k-moe, that's good to know.

Could that have cost me some power?

BTW the reason I re-posted elsewhere if you noticed that was page two wasn't showing up in my browser so I thought the post here was lost and I figured it was more appropriate for another thread anyway.

 

Yes, not enough clearance is similar to advancing the exhaust valve timing (the valve starts opening sooner than it should) as well as closing later than it should, as well as throwing off the relationship of valve timing between the intake and exhaust.

Good way to throw off horsepower....

 

Well hopefully we are on to something here then. The motor seemed to be running well, and sounded fine, just didn't have the power it should have especially at higher revs.

Will let you know what happens when we button it back up next weekend.