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Low compression mystery - advice?

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My 2001 DRZ400S has 13,000 miles on it, unknown maintenance schedule prior to my buying it last year at 12K miles.  I noticed some slight coolant and oil loss without apparent external leaks.  When I added coolant and ran the bike to watch for flow I noted a very tiny flow of bubbles coming up.  I should note that the bike seems to run very well, and seems to me (having never ridden a DRZ400 before) to have plenty of power.

 

To lower the chances of a motor failure during a planned Michigan Upper Peninsula ride next month I decided to do a compression check.  Bad result - 60 psi.  I bought a better compression tester - still 60 psi.  I checked it on my lawn mower - 140 psi.  I added oil to the cylinder through the plug hole on the DRZ and tested again - 90 psi.

 

So I ripped her down tonight.  I would like your help interpreting the pictures.  Other info - valve clearances were perfectly in spec, cam chain tension is sweet with a manual tensioner.  I could not find my feeler gauges that go smaller than .25mm so I could not measure ring to groove gap or plain end gap of the rings, but according to my caliper the cylinder is exactly 90mm all around, as is the piston, and the free gap of the first and second rings is in spec, as well as the groove thicknesses, although the factory manual lists two sets of numbers for the first ring thickness and gap for some reason, leading to some confusion for me there...

 

The cylinder is smooth with no grooves as is the piston.  Nothing is shouting out to me as the cause for the low compression unless it is the head gasket?  I am not sure weather to just:

 

a) throw on a new gasket set on.  

 

B) Throw rings on in addition to a.

 

c) new piston in addition to a and b.

 

d) Hone cylinder in addition to a, b and c

 

e) Bore cylinder to next size and do a, b and c.

 

I really want to do the cheapest fix possible as I have so little free cash to spare.  Help is appreciated!

 

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F: for the price of boring the cylinder buy a cylinder works big bore kit.

60 is low, but the automatic decompression on the exhaust cam can skew your readings. A leak down test is the preferred method of checking the engine.

Loss of coolant and bubbles sounds to me like a head gasket issue.

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F: for the price of boring the cylinder buy a cylinder works big bore kit.

60 is low, but the automatic decompression on the exhaust cam can skew your readings. A leak down test is the preferred method of checking the engine.

Loss of coolant and bubbles sounds to me like a head gasket issue.

According to the service manual (and a video I saw of someone on youtube performing a compression test on the DRZ), with the auto decompression the reading should be 135 psi.  I don't think I need a bore, but not sure if a hone is recommended for this cylinder (is there a nikasil or some other coating that would be damaged?) or just throw it back together with new gaskets.  The measurements are so perfect from what I have measured so far that everything is in spec as far as the cylinder, piston and rings go.

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By the looks of the piston crown and head, it has been burning some oil.

Although you say it has only done 13K, it is a 13 year old bike and may not have had the best maintenance in that time.

Depending on how much money you want to spend, at the lest, give it a hone with a new set of rings and gaskets.

After that, only you can decide if you want to spend more. I would be apprehensive about doing a BB without doing new rod and getting the head reconditioned.

Not because it is worn out,  just that you don't know it's history, a lot can have happened in 13 years, regardless of how many miles it has done.

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The Big Bore is a option , but , you say you want to go for the cheapest price .

If the cross hatch marks are still visible , and the measurements are to spec , fit new OEM rings , piston pin , clips . new gaskets .

That leaves the Cylinder Head , you need to make sure the valves are in good condition and not leaking .

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According to the service manual (and a video I saw of someone on youtube performing a compression test on the DRZ), with the auto decompression the reading should be 135 psi.  I don't think I need a bore, but not sure if a hone is recommended for this cylinder (is there a nikasil or some other coating that would be damaged?) or just throw it back together with new gaskets.  The measurements are so perfect from what I have measured so far that everything is in spec as far as the cylinder, piston and rings go.

 

look at the piston- the machine marks on the skirts are still there = great condition

look at the cylinder - the nikasil is still undamaged and not gouged = great condition

= get rings, wrist pin, keepers and consider this area good, reassemble

 

the autodecompression must be disabled to get a reliable reading on a compression gauge. the bike simply won't run with 60psi. iirc 90psi is the low limit for actually firing/running. what you are seeing is the autodecomp still working while the engine is spinning slowly. that is the only reason for the low numbers. 

 

the bubbles in the coolant and loss of oil/coolant points to a bad head gasket. i would replace that, new rings, new wrist pin, keepers, and enjoy the bike another 20,000 miles or so. if you want to have the cylinder magnafluxed for cracks, that's fine, but i don't think you need it. 

 

soak the piston in "pbblaster" and the carbon will fall off. clean the ring grooves with an old ring, carefully, do not remove aluminum ;-)

soak the cylinder in pbblaster also, that ridge of carbon will come off with a brown scotch bright, then you can lightly scuff it for a cross hatch, but i doubt you'll accomplish much with that super hard nikasil coating. a very very light honing might make a pretty pattern, or ruin it, depending on who has the controls. ;-)

flip the head upside down and pour pbblaster in the depression. if it leaks out the intake/exhaust runners, the valves aren't sealing or there is a crack. the side benefit of this is all the carbon will wipe off with a rag. you might want new guide seals while the head is off too. 

really, the engine looks great. 

Edited by ohgood
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While you have the head off turn it upside down and fill the combustion chamber with solvent.then blow compressed air into the intake and exaust ports. If you see bubbles you need to service the head and put in new valves.your piston and cylinder look fine. If your going to use the same cylinder use a ball home to clean out the cross hatches and install new rings on the piston

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Here's how I determined I needed a new piston.

 

DSC03478.jpg

 

I just deglazed the cylinder put new rings pin and clips, gaskets, cleaned the head and valves and put back together, has been running fine since. Maybe it lacks in power a bit vs a complete rebuild but I'm confident it won't leave me stranded in the desert or mountains.

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Thanks for all of the awesome advice!  I bought a Wiseco kit with piston, rings, pin, clips and gaskets.  A little piece of mind for $205 after taxes and Saturday shipping on Amazon Prime.  I have a few questions still.

 

1. I am planning on "deglazing" a bit using one of the brown/maroon Scotch-Brite pads I bought in the Home Depot paint section.  Any instructions on what to do?  Do I use some sort of liquid such as the PB Blaster I also bought on the pad/cylinder walls as a lubricant while deglazing with the pad?  Maybe motor oil? Dry?

 

2. How do I remove the gasket residue from the head and cylinder mating surfaces?  Will the PB Blaster Catalyst Solvent take care of it or do I need to scrape?  I obviously am nervous about scratching the mating surfaces.

 

3. Coat gaskets with copper gasket sealant or leave bare?

 

4. Torque sequence and ft. lbs advice?

 

5. When removing the piston pin circlips, one of the little beauties went flying down onto the crankshaft and I sorta saw/heard it bounce either out of the crankcase or further in.  It was like a bullet ricocheting!  When I look and gently turn the crank I can't feel any resistance like it is lodged in there, nothing comes out when I put a magnet in and fish around where I can reach and I can't see anything with a flashlight. However I can't find it in my mess of tools and parts scattered around the bike in my basement.  How likely is it that it could be in the crankcase and what should I do?

 

6. Should I use plain motor oil or some kind of special oil on the piston/rings/cylinder when reassembling?  I have two-stroke oil available as well as motorcycle four-stroke...

 

7. For break-in do I use non-synthetic 10w-40 (I know, no energy conserving due to clutch), or just run the 20w-50 I was planning on using at my next oil change?

 

8. Should I be able to compression check it after reassembly and before running and get a decent idea of what the final reading will be, or does it need break in before any meaningful numbers will show?  Opinions on break-in procedure with new piston/rings but no honed nikasil cylinder?

 

Any opinions on why was the damned bike was running so decently with such low cold compression (somewhere between 60-90, lets assume auto decomp did not have enough inertia to stop working)? Freakin' tough to get a hot reading with all of the crap you have to remove to get to the plug!

 

The only weird thing I noticed was an inability to maintain a nice and consistent RPM with various throttle openings in neutral.  Could be normal.  Mikuni carb clean and rebuilt using JD kit 155 Main, 25 pilot and screw about 5 turns out, blue needle on 4th position.  3x3 mod, stock exhaust. Plug looks clean and light tan.  Pulls great, grunt down low for slow rock climbs, lofts in 1st and second when throttle cracked and will crack an indicated 90 MPH with 15/44 sprocket combo and I weigh 250 lbs.  Seems to heat up at a normal rate and fan kicks in only occasionally like I expect. 

 

Thanks in advance for advice.

Edited by seekerhiker

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Oh man, circlip in the bottom end is no bueno. Don't even bother with everything else right now, find that sucker!

I'll find it.  Maybe shoot the air compressor nozzle in there to see if it shoots out, then scour the basement looking for it - water heater, furnace, laundry pile, tools and parts galore all within a 10-ft radius of the bike... Yuck work!

 

In the meantime, any answers to the above?  I think with the Scotch-Brite I'll use the PB Blaster and scrub abound for a few minutes, then brake cleaner to inside surface of cylinder whilst wiping with a rag until spotless, then dishwasher?  Objections?

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1. I am planning on "deglazing" a bit using one of the brown/maroon Scotch-Brite pads I bought in the Home Depot paint section. Any instructions on what to do? Do I use some sort of liquid such as the PB Blaster I also bought on the pad/cylinder walls as a lubricant while deglazing with the pad? Maybe motor oil? Dry?

* I always used a green scotch brite pad and oven cleaner, then wash till it wipes clean with a paper towel.

2. How do I remove the gasket residue from the head and cylinder mating surfaces? Will the PB Blaster Catalyst Solvent take care of it or do I need to scrape? I obviously am nervous about scratching the mating surfaces.

*PB Blaster or there are specific gasket removing solvents you can use. Scrape anything left over.

3. Coat gaskets with copper gasket sealant or leave bare?

*your choice, I use it for peace of mind

4. Torque sequence and ft. lbs advice?

*torque in a star patternImageUploadedByThumper Talk1402691565.303489.jpg

Edit: thought cylinder and head torque specs were on this list but they aren't, need to check the manual

5. When removing the piston pin circlips, one of the little beauties went flying down onto the crankshaft and I sorta saw/heard it bounce either out of the crankcase or further in. It was like a bullet ricocheting! When I look and gently turn the crank I can't feel any resistance like it is lodged in there, nothing comes out when I put a magnet in and fish around where I can reach and I can't see anything with a flashlight. However I can't find it in my mess of tools and parts scattered around the bike in my basement. How likely is it that it could be in the crankcase and what should I do?

* as a last resort flush the motor with diesel fuel, turn it upside down and shake the shit out of it.

6. Should I use plain motor oil or some kind of special oil on the piston/rings/cylinder when reassembling? I have two-stroke oil available as well as motorcycle four-stroke...

*whatever break in oil you choose

7. For break-in do I use non-synthetic 10w-40 (I know, no energy conserving due to clutch), or just run the 20w-50 I was planning on using at my next oil change?

*use non synthetic for break in

*break in first then do a leak down test. For break in just ride it like you stole it and change the oil after 50, 500, then 1000 miles

8. Should I be able to compression check it after reassembly and before running and get a decent idea of what the final reading will be, or does it need break in before any meaningful numbers will show? Opinions on break-in procedure with new piston/rings but no honed nikasil cylinder?

Edited by Gsxrstuntdrz
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Thanks for all of the awesome advice!  I bought a Wiseco kit with piston, rings, pin, clips and gaskets.  A little piece of mind for $205 after taxes and Saturday shipping on Amazon Prime.  I have a few questions still.

 

1. I am planning on "deglazing" a bit using one of the brown/maroon Scotch-Brite pads I bought in the Home Depot paint section.  Any instructions on what to do?  Do I use some sort of liquid such as the PB Blaster I also bought on the pad/cylinder walls as a lubricant while deglazing with the pad?  Maybe motor oil? Dry?

 

the pbblaster makes everything that isn't nikasil fall away, you won't scuff the nikasil with teh scotch brite, wet, dry or sideways ;-) it's carbide, basicly

 

2. How do I remove the gasket residue from the head and cylinder mating surfaces?  Will the PB Blaster Catalyst Solvent take care of it or do I need to scrape?  I obviously am nervous about scratching the mating surfaces.

 

yes, pbblaster will loosen it. i use a piece of thin copper about 2" wide, which is filed sharp. the copper is softer than the aluminum, so it will loose its edge quicker than the aluminum will scratch, normally. 

 

3. Coat gaskets with copper gasket sealant or leave bare?

 

coat with spray copper gasket, yes

 

 

4. Torque sequence and ft. lbs advice?

 

43 ft lbs, but i don't recall the sequence off hand

 

5. When removing the piston pin circlips, one of the little beauties went flying down onto the crankshaft and I sorta saw/heard it bounce either out of the crankcase or further in.  It was like a bullet ricocheting!  When I look and gently turn the crank I can't feel any resistance like it is lodged in there, nothing comes out when I put a magnet in and fish around where I can reach and I can't see anything with a flashlight. However I can't find it in my mess of tools and parts scattered around the bike in my basement.  How likely is it that it could be in the crankcase and what should I do?

 

don't turn the crank until you -KNOW- you have it in your hot little hand, and about to throw it in a garbage can. that will make a mess of things if it gets into a bearing or timing chain

 

6. Should I use plain motor oil or some kind of special oil on the piston/rings/cylinder when reassembling?  I have two-stroke oil available as well as motorcycle four-stroke...

 

twostroke oil is fine, or regular old engine oil, whatever

 

7. For break-in do I use non-synthetic 10w-40 (I know, no energy conserving due to clutch), or just run the 20w-50 I was planning on using at my next oil change?

 

20w50 is fine. don't turn it into an oil thread, it's just 3-4 minutes of running that matters ;-) 

 

 

8. Should I be able to compression check it after reassembly and before running and get a decent idea of what the final reading will be, or does it need break in before any meaningful numbers will show?  

 

i'd guess 140-160psi, but you MUST disable the auto-decompression mechanism to get a read, with the throttle fully open. 

 

Opinions on break-in procedure with new piston/rings but no honed nikasil cylinder?

 

ride it like ya stole it, lots of full throttle acceleration/decelleration - then stop at a gas station and check the oil level. ride it the same way home, check oil level again. after that, whatever. no high speed riding or high rpm sustained engine speeds until it's got a few hundred miles on it. 

 

 

Any opinions on why was the damned bike was running so decently with such low cold compression (somewhere between 60-90, lets assume auto decomp did not have enough inertia to stop working)? Freakin' tough to get a hot reading with all of the crap you have to remove to get to the plug!

 

exactly that, any reading without disabling the auto decomp is useless

 

 

The only weird thing I noticed was an inability to maintain a nice and consistent RPM with various throttle openings in neutral.  Could be normal.  Mikuni carb clean and rebuilt using JD kit 155 Main, 25 pilot and screw about 5 turns out, blue needle on 4th position.  3x3 mod, stock exhaust. Plug looks clean and light tan.  Pulls great, grunt down low for slow rock climbs, lofts in 1st and second when throttle cracked and will crack an indicated 90 MPH with 15/44 sprocket combo and I weigh 250 lbs.  Seems to heat up at a normal rate and fan kicks in only occasionally like I expect. 

 

Thanks in advance for advice.

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While you have the head off turn it upside down and fill the combustion chamber with solvent.then blow compressed air into the intake and exaust ports. If you see bubbles you need to service the head and put in new valves.your piston and cylinder look fine. If your going to use the same cylinder use a ball home to clean out the cross hatches and install new rings on the piston

mickeydee,

I just did this test and wouldn't you know it, when high pressure air is directed just right it causes tiny foamy bubbles on one part of the exhaust valve and one part of the intake valve on the same side of the motor.  Other side nothing.  PB Blaster stays level in combustion chamber dome with no leaks or loss of level otherwise.  I was thinking of doing the "Valve Grinding for Broke Folks" (really lapping) as shown in this video:  http://youtu.be/TrKINFBsQD8

 

Any thoughts?  Leave it alone maybe?  I had to shoot 140 PSI right out of a 1/4" tipped nozzle and right on the valve's topside to get the bubbles.  Is such a tiny leak significant?  Does it contribute more to compression than rings?

 

Everyone else - Brake Cleaner and PB Blaster cleaned the gasket sealing surfaces off just fine.  I Scotch-Brited the cylinder, but it didn't seem to do squat.  After a wipe or two on the inside with brake cleaner it was clean as a whistle.  It is in my dishwasher now getting a spa treatment.  ;)

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I decided I am going to do nothing to the valves.  I realized that lapping would affect valve clearance and I would need to start replacing shims and that is a whole new can o' worms.  Rings, gaskets and ride.

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I decided I am going to do nothing to the valves.  I realized that lapping would affect valve clearance and I would need to start replacing shims and that is a whole new can o' worms.  Rings, gaskets and ride.

As you have removed the piston, replace circlips as well with new ones. :thumbsup:

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Worked all day on the project, worn out now.  Wiseco piston is a bit heavier than stock and rings are WAY beefier than stock.  They also sent me an E model base gasket only. What a PITA to get the piston/rings back into the cylinder!  Then after reassembling I found out I put the front cam chain guide in wrong.  Head off, fixed that and discovered the cam chain was off the sprocket - head came off again to see in there and get it back on the sprocket.  

 

So now that I have torqued and untorqued my head/cylinder multiple times I have decided that I need even more new gaskets.  Ordered.  

 

Is engine oil on a head gasket a no-no?  Seems nearly impossible to keep oil needed to install piston off of the gasket...

 

Also, the factory calls for 35 ft lbs of torque on the head bolts, but that seems crazy low.  I know that taking them out the first time that they were at what felt like 130 lbs.  Is that just normal heating/cooling that caused that or did someone mess up installing the bolts before I owned it?

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Worked all day on the project, worn out now.  Wiseco piston is a bit heavier than stock and rings are WAY beefier than stock.  They also sent me an E model base gasket only. What a PITA to get the piston/rings back into the cylinder!  Then after reassembling I found out I put the front cam chain guide in wrong.  Head off, fixed that and discovered the cam chain was off the sprocket - head came off again to see in there and get it back on the sprocket.  

 

So now that I have torqued and untorqued my head/cylinder multiple times I have decided that I need even more new gaskets.  Ordered.  

 

Is engine oil on a head gasket a no-no?  Seems nearly impossible to keep oil needed to install piston off of the gasket...

 

Also, the factory calls for 35 ft lbs of torque on the head bolts, but that seems crazy low.  I know that taking them out the first time that they were at what felt like 130 lbs.  Is that just normal heating/cooling that caused that or did someone mess up installing the bolts before I owned it?

Sounds like your making hard work of it M8.

As you have not actually run the engine with the new head gasket, I would still use it.

Just clean and wipe off excess oil.

Torque is 43 ft lbs for head bolts, (35 is believed to be a miss print) use some new oil on the threads on assembly.

The base gasket is usually 3 piece, "E" gasket is either the top or bottom of that 3 piece gasket but not the centre piece.

I normally just run my finger round the bore, front and back of piston with a sniff of fresh oil on it, no need to drown it, you only get excessive smoking on start up.

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I ordered this digital torque adapter to make sure I get it right. http://www.amazon.com/gp/product/B004VYUKTC/ref=oh_details_o01_s00_i00?ie=UTF8&psc=1

My current 1/2" torque wrench is a piece of crap - I can't figure out when it actually "clicks" anymore, and I don't trust my feel for that exact amount of torque.

 

The base gasket supplied from Wiseco was just one layer - but the head gasket was 3 layers...?  Is it supposed to be?  I guess I should have realized it would be a 1 layer base because it mentioned 12.2 to 1 compression, and I should have remembered a stock S is 11.3 to 1.  It just said S and I ordered.  I need to be able to run on 87 because I will only have that available some of the time in Michigan.

 

I also ordered some spray copper.  Should I do both sides of base and head gaskets?  Just one layer or more?

 

I needed a fair amount of oil to work in the rings by hand to get the piston into the cylinder, those suckers are TIGHT on the Wiseco piston.  I am surprised my fingers are not shredded by compressing those rings with them, they feel so sharp!

 

For others doing this job, learn from my hardships.  These are the things to watch for that I did not come across in my research.

 

1. Loosen right radiator, then remove thermostat housing with head loose and movable rather than try to remove the lower right radiator hose.  Not enough hose length to work it off easily without bending the aluminum.

 

2. Install front (exhaust side) cam chain guide while looking down into cam chain chamber on cylinder.  You will see a grooved area in front of the cam chain sprocket that it sits in, then use a bit of force to get the nipples that stick out from the sides of the guide to seat properly in the front top surface of the cylinder before setting the head back on.

 

3. Be careful to look down into the cam chain chamber and make sure the chain is on the right (outside-most) little teeth of the sprocket.  When the bike is on the side stand the chain tends to slip off of the teeth.  Pull the chain tight and rotate the motor to be sure the chain is turning and not just turning a but then slipping, or it could be just riding on the bare part of the shaft.  Keep that tension on the chain and keep checking it as you install the head.  Don't let it slip back off the teeth by sliding to the left a hair!  Use a partner or a bungee with some tension!

 

Be super careful with that whole oil expander ring deal.  You have to do a trial compression of the expander and it's rings before inserting into the cylinder to make sure the ridges touch nicely and don't overlap when compressed.  Those thin rings on the top and bottom of the oil expander thingy love to come out of the grooves when installing into the cylinder, so go slow and keep doing 360 degree checks around the piston as you insert it, especially on those rings.  Any sudden bind - stop and reassess!  You will see that the front edge of one of those damn rings has come out of the groove again.

 

I also didn't take out the carb.  I should have completely removed it.  It gets in the way when manipulating the head around, as does the cam chain tensioner.  Mine is a manual one, but I just took it out after wrestling too much with the heavy head.

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DO a search for piston assembly.

 

Two words to the wise; Wash anything you Scotch Brite in the dishwasher, it's not magic, its polyamine fiber with grit in it. Think sandpaper.

 

Second; assemble the piston and rings DRY. Excess oil in the ring grooves will keep the rings from sealing properly.

 

 

I needed a fair amount of oil to work in the rings by hand to get the piston into the cylinder, those suckers are TIGHT on the Wiseco piston.  I am surprised my fingers are not shredded by compressing those rings with them, they feel so sharp!

 

What about usng a ring compressor?

Edited by Bermudacat

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