Maxim X low compression

Ugh, compression test just showed 105, 143, 80, 100 for numbers. Going back outside to put a teaspoon of oil in the cylinders and see if that helps.

Bummer after doing valve clearance, carb breakdown and clean, and a coil replacement. Wish I'd done the compression test first. Maybe clearance measurements then compression test.

 

With 1 tsp of 20W-50 oil in each cylinder:

#1 went from 105 -> 148
#2 went from 143 -> 218 (!?)
#3 went from 80 -> 140
#4 went from 100 -> 147

So it looks like rings all around, and possibly something else in #2? Something caked on the head? I shouldn't have that high a reading, right?

So how bad a job is this? Looks like I might be pulling the engine to "winterize" this year.

 

How many strokes did you allow on your comp' test, should be 3-4 max.
Yes to the ring job & not good to run it with that one jug low on comp'.

 

Hey Wiz! Thanks for the response.

I let it go as many as 8-10 strokes I think... until the needle stopped advancing much. It was pretty close to my numbers after 3-4 though.

Yamaha manual says if the measure with the oil added is
- higher: worn or damaged pistons
- same as without oil: defective ring(s), valves, cylinder head gasket or piston is possible
- above maximum level (165 psi): Inspect cylinder heat (sic), valve surfaces, or piston crown for carbon deposits

Which is not what I expected. I thought rings (and/or piston damage) if the reading is higher, looks like they're saying rings if it reads the same? That doesn't make sense to me. Also, pretty sure that's a typo on the "above maximum level" situation... should be inspect cylinder head, not heat.

Time to browse Len's catalog for rings...

 

You might have mis-read that, if the readings are higher with oil added = worn rings or damaged pistons, if the readings stay the same, the prob' is with the valves, seats etc.
Were you testing with the throttle wide open & the air filter removed?

 

If you do decide to do the piston rings (if that is what it is) the actual piston rings are not too bad. IMO, it's getting the new head gasket kit, and making sure the timing is set right. Just take your time. It's a time consuming project.

 

Fun fact: When checking mine we found 80 in #1, then 81 in #2. After the first we were really scared, after the 2nd we were equally scared. Having tested all 4 we found they were all 80+/-3. Turns out they were all about perfect, but the meter was bad.

 

Wow! Definitely something weird with that 2/3 pair. I just got my GPz back together, which had bent valves on all cylinders, but was especially bad on #3. My compression numbers were mixed but low, and non-existent on #3, before. Adding oil did help all of them. I then got yelled at by a race guy who did some tuning work for me. He said the oil trick is WWII vintage for use in the field and shouldn't ever be used these days.

Anyway, once I had the head off, the cylinders looked good enough that I didn't do rings. Post-reassembly I was getting 110psi cold and dry across the four cylinders. I'm at 6000 feet elevation, so I'd say that's OK.

Did you check your compression cold, or warmed up?

One thing you could try, which was helpful for me, would be to pull the cams and then use a compressor to push air into the cylinders and see if you can feel or hear air blowing out through the intake or exhaust (indicating bent valves, bad clearance, or bad valve seats).

Once I had mine all apart, I found that a bench lathe, if you have one, is very helpful for spotting bent valves. Just chuck 'em up, spin 'em, and see if the head wobbles. A drill press would probably serve just as well for that.

By the way, how was the bike running, regardless of the comp numbers? Any smoking or popping?

Cheers,
Paul

 

Hey Paul,

Thanks for the response. The compression test was mostly cold... bike was a little warm when I started but I finished after breaking for dinner.

I've heard your suggestion called a "leak-down test" and I think that's a good idea. I might try it just for kicks, but I found a motor machine shop not too far away that quoted some prices I thought were reasonable to look things over, cut new valve seats if needed, bore out the cylinders, etc. I may just break the engine down and lug parts over there.

The bike was running better after cleaning carbs, adjusting valve clearance, DynaCoil conversion, colortuning and syncing. But seemed it seemed a little underpowered; worst thing would be when I'd give it some throttle in the lower RPM range and the engine would almost buzz with this loud, violent-sounding noise. I wondered if I had some bad valve seats. No smoking or popping. I thought it might have been a problem with ignition where the spark wasn't setting off the mixture, but it was detonating at the wrong time. I don't know, I'm not a mechanic (but I feel like I will be soon at this rate.)

 

Ok, I'm the slowest mechanic ever. I pulled the engine this year and took the head and pistons/jugs to a machine shop. They lapped the valves, inspected the cylinder walls (said they looked fine) and returned the parts to me.

I'm ready to reassemble but the paint on the exterior (even the interior) of these parts is destroyed. The cylinder jugs have hardly any finish left, the top cam case has most of its finish, the cylinder head (the section with the valves) is a mess.

Obviously they used some solvent or something that ate the paint:


The exhaust side needs to be repainted:


The intake side needs to be repainted:


And even inside the head there is peeling paint:


Note that they reassembled the valves (with new valve stem seals I provided via Chacal).

I'm thinking I may need to take this back to the shop, have them remove the valves, strip all the paint, reassemble the valves, and then re-paint the exterior (can probably leave the interior unpainted, right?

Has anyone dealt with this? Suggestions appreciated...

 

Never dealt with that type of issue before. The inside of the cylinder head will have to get all that paint removed or it could cause some issues down the road.

As far as the exterior goes, I would assemble it, then paint it with high temp engine paint. I've had good luck with brands that are rated for 500 degree +.

 

This is the most critical, the above advice in regard to the exterior is probably the best course of action as well.

What beats me is why the head was painted INSIDE, around the valves, to begin with. Never seen such a thing (but then I've never had an "X" motor apart before.) I'm sure it would be ok to subsequently leave it "raw."

 

X engines have the inside painted, then machined. Not sure why Yamaha added that extra step in the process? It does aid in helping the oil drain back to the sump, but is it necessary? Not really.

 

Ok, so I took the parts back to the shop, had them pull the valves and soda blast the peeling paint off the inside and outside. The paint inside the top cam case didn't look too bad so they left that alone - probably couldn't blast that anyway without damaging the bearing surfaces.

So I had a buddy paint the exteriors of the parts separately.

 

Now I'm in trouble. I was testing the piston fit on my #3 cylinder, using the old rings. In the process, I put a scratch in the wall of the cylinder.





Tried honing it out, but it's still there. Pictures are post-honing. It's on the skirt, and the scratch ends 44mm from the top of the cylinder wall. I believe the stroke is 48mm, so not sure how much this will affect compression. I think it looks worse in a macro shot of the cylinder wall than it actually is. Still kicking myself.

Chaz

 

Good to see you got the paint cleaned up on the inside of the head.

On the issue of the scratch, you'll probably have to work with slightly coarser grit to get more of the scratch out, say a 220-320 piece of emery cloth (working perpendicular to the scratch). Then hone it again to get your cross-hatch pattern back.

When staggering the end gaps on the rings during assembly, make sure each gap is at least 90 degrees away from the original scratch area. With a 48mm stroke you should be OK, being the top compression ring will barely be it that area when at the bottom of the stroke, and the lower oil ring will seal it up just above the original area that you scratched when coming up from the bottom of the stroke. Therefore you shouldn't have an issue with that cylinder using oil, and when the rings are broken in the compression will be comparable to the other cylinders.

 

Re: Maxim X low^H^H^H fixed compression

Quite a bit of progress on the Maxim-X: finished engine reassembly last fall. New rings looked good, initial compression test by hand looked promising, engine was reinstalled in the frame. Checked float levels in the carbs before installing and gas ran all over the place (replaced fuel tee with brass version from Chacal). Unfortunately, it was getting to be November and I don't have a heated garage. I couldn't get the carbs in the intake boots, figured they were just too cold.

Last week I resumed work, heated the boots with a hair dryer, got the carbs in... but the airbox-to-carb boots had shrunk. Finally on Saturday I tied up loose ends, checked the fluids, installed the battery, and hit the start button. Three minutes of confusion ensued, then I figured out I had somehow swapped plug leads 3 and 4. Fixed that and she started right up! Quick sync and idle adjustment, then I noticed it was running hot... just into the red.

Replaced the thermostat (thanks to Maxim-X for the tip on aftermarket thermostats, got a $6 thermostat from a 1998 Hyundai Sonata vs. the $40-60 for a Yamaha version) and verified the fan was coming on... temperature was stable.

Went for a few limited test drives! What a good feeling to finally have this bike running again. Here are a few pictures:

Engine broken down (note 5-valve cylinder recesses)


The so-called mechanic:


Assembled engine:


New fuel tee (thanks to Chacal)


Bike in draiveway:


Coming back from first ride:
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Now replacing my 1997 tires...

Thanks all for the help and advice! More questions to come, for sure.

 

I love it when a plan comes together.

Congratulations, and good work. You're no longer a "so-called" mechanic, you've graduated! That was your thesis, and you just passed.

Now ride safe. Be sure to scuff the new tires in for a few hundred miles.

 

Looks nice! Now you get to appreciate all your hard work.

And don't stop at just putting new rubber on it, make sure you go through the braking system as well. That way you'll be confident in your bikes ability to go beat up on some Harley's.

Tony

 

Nice work man, congrats on the restoration. Nice to see the bike out and about and get used to how that power comes on when you crack it open, for only being a 750 it can be a real eye-opener if your not ready!