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No Compression After Top End Rebuild
- Thread starter bcware
- Start date
Shaun Chandler
XS400 Addict
Hey Bc push it to about 1/2" from the top of the cylinder or mabey abit lower and use your piston to push the ring after you insert it by hand. This squares the ring up in the bore and makes for an accurate measurment.
OK, all of the rings were measured.
For reference the maximum range in the Haynes says 0.016" for the top and middle rings.
The rings were placed squarely 20 mm (0.8") in from the top
Right top: 0.017"
Right mid: 0.015"
Left top: 0.015"
Left mid: 0.014"
It appears as though I have some uneven ring wear as opposed to excessive barrel wear. I can still see the original cross-hatching in the travel area of the pistons, but of course there are some very light vertical and horizontal wear marks. None of the wear marks can be perceptively felt with my finger tips, so they are very shallow.
The letter "N" faces the sky when installed, correct? I know I read that the writing faces up somewhere, but I couldn't see it mentioned in the Haynes just now.
Oh, and the bike only has about 11,000 original miles on it.
I think the root of all my problems was the leaking valve seals. A new complete gasket set is on order. Are there any tips for installing the valve seals other than not being an idiot and wiping off the lapping compound in the ports? Last time I simply pressed them on the guides while the valves were out, lubed the valve stem seal, guide, and valve stem with motor oil, and pressed the valves in slowly.
For reference the maximum range in the Haynes says 0.016" for the top and middle rings.
The rings were placed squarely 20 mm (0.8") in from the top
Right top: 0.017"
Right mid: 0.015"
Left top: 0.015"
Left mid: 0.014"
It appears as though I have some uneven ring wear as opposed to excessive barrel wear. I can still see the original cross-hatching in the travel area of the pistons, but of course there are some very light vertical and horizontal wear marks. None of the wear marks can be perceptively felt with my finger tips, so they are very shallow.
The letter "N" faces the sky when installed, correct? I know I read that the writing faces up somewhere, but I couldn't see it mentioned in the Haynes just now.
Oh, and the bike only has about 11,000 original miles on it.
I think the root of all my problems was the leaking valve seals. A new complete gasket set is on order. Are there any tips for installing the valve seals other than not being an idiot and wiping off the lapping compound in the ports? Last time I simply pressed them on the guides while the valves were out, lubed the valve stem seal, guide, and valve stem with motor oil, and pressed the valves in slowly.
lhaolpa
XS400 Junkie
Adding oil seals off the rings to determine if your problem is rings or valves. Since the compression went up after adding oil,sealing the rings,that's your problem. How did you lap the valves? Did you test for leaks[probably not]by filling the chamber with water,waiting a while,then seeing if there are any leaks? that's what you have to do to tell if they were lapped enough. lha
I did not do a leak test on the valves before I assembled them, but they were very smooth after I lapped them with no visible blemishes. I just finished lapping them again; do the springs need to be installed to test for leaks?
The rings were definitely causing the loss of compression, but I think a cascade of events starting with valve seals failing lead to this; i.e. the valve seals failed and allowed oil to leak into the intake/exhaust ports and into the combustion chamber. Excess oil dripping off the valves can foul the plugs allowing fuel to build up and wash out the pistons. If oil is coming out of the ports it is going to enter the carbs and headers. If it enters the carbs I have to imagine the resulting soupy gas/oil mixture wont burn, but it could still wash out the rings further.
The rings and barrels don't seem bad enough to be causing these problems and I see no signs of failure anywhere else.
The rings were definitely causing the loss of compression, but I think a cascade of events starting with valve seals failing lead to this; i.e. the valve seals failed and allowed oil to leak into the intake/exhaust ports and into the combustion chamber. Excess oil dripping off the valves can foul the plugs allowing fuel to build up and wash out the pistons. If oil is coming out of the ports it is going to enter the carbs and headers. If it enters the carbs I have to imagine the resulting soupy gas/oil mixture wont burn, but it could still wash out the rings further.
The rings and barrels don't seem bad enough to be causing these problems and I see no signs of failure anywhere else.
lhaolpa
XS400 Junkie
To square the rings in the bore,push the ring with a piston a little way into the bore,then measure the gap.Then measure at a point a ways up from the bottom to get an idea how much taper the cylinder has.You might have to rebore,and put new oversized rings and pistons in. lha
Do my ring measurements seem OK? The bike has always run fine. I also cannot see how a re-bore and new pistons and rings is an economical option. I would think the cost would easily exceed the price of a new engine and/or complete motorcycle.
$180 for pistons
$120 for rings
$150 for a bore
+ misc bits of hardware and shipping. No way this thing is getting a re-bore.
$180 for pistons
$120 for rings
$150 for a bore
+ misc bits of hardware and shipping. No way this thing is getting a re-bore.
Shaun Chandler
XS400 Addict
I know what you mean Bc. Are you looking at nos yamaha stuff? You may be able to source after market stuff far cheaper although its going to take you time. Thats what I'm planning on doing for my rebuild just haven't got around to the pistons yet.
Are your pistons shot? I think you can just have them knurled to increase their dia to account for the bore.
Shaun
Are your pistons shot? I think you can just have them knurled to increase their dia to account for the bore.
Shaun
I don't see any damage to the bore, pistons, or rings. I really think the rings were just stuck and/or in the wrong orientation. The Haynes instructions for installing rings is very poor for a first-timer. I just watched a Box Wrench video on how to install them properly. There is a LOT not covered in the manual.
I was looking at new parts from bikebandit. There is little to no selection on ebay and most of it is even more expensive.
I was looking at new parts from bikebandit. There is little to no selection on ebay and most of it is even more expensive.
Shaun Chandler
XS400 Addict
I know the ebay stuff is stupid expensive. At a certain point you have to know when to say enough is enough. As long as you have enough compression to make it run.
Shaun
Shaun
I did more checking and found the cause of the oil in the intake and exhaust ports; the valve guides are worn. The lapping compound and valve stem seals probably had nothing to do with my problems. There is a fair amount of wobble on both exhaust valves and only a slight wobble on the intake side.
This explains the oil in the ports, fouled plugs, and heavy carbon buildup on the base of the valve stem and on the piston. The heavy carbon deposits in the piston grooves caused the rings to stick. When the rings stick they, obviously, are not expanding, forming a good seal, or keeping compression.
So, it looks like I need new guides or the guides need to be bored out and lined.
This explains the oil in the ports, fouled plugs, and heavy carbon buildup on the base of the valve stem and on the piston. The heavy carbon deposits in the piston grooves caused the rings to stick. When the rings stick they, obviously, are not expanding, forming a good seal, or keeping compression.
So, it looks like I need new guides or the guides need to be bored out and lined.
The prices on bikebandit for these guides is pretty high, but there is someone selling them on ebay for a lot less.
The part number for these guides is 4H7-11133-10, but the auction and cmsnl mention that they are superseded by 4H7-11133-11. Assuming the superseded part is better quality, which should I get?
4H7-11133-10 is $61 shipped from this guy on ebay
4H7-11133-11 is $94 + shipping from bike bandit
Bikebandit lists their own part numbers, but they note that this is an "alternate part" and I am assuming they have the 4H7-11133-11 instead.
The part number for these guides is 4H7-11133-10, but the auction and cmsnl mention that they are superseded by 4H7-11133-11. Assuming the superseded part is better quality, which should I get?
4H7-11133-10 is $61 shipped from this guy on ebay
4H7-11133-11 is $94 + shipping from bike bandit
Bikebandit lists their own part numbers, but they note that this is an "alternate part" and I am assuming they have the 4H7-11133-11 instead.
I had my guides done using modern material valve guides. they are pretty much standard, its the reaming the size to each valve is where the $ is (and skill) after its done the valves need to be kept in their respective homes.
Yes, everything goes back where it came from. For giggles I even put them on opposite sides to see if they wiggled less; nope. It feels the same no matter where they go.
There is a good machine shop not far from here and the prices seem reasonable. They seem to do every kind of valve job one can imagine. I may have mine bored with new inserts pressed in. It may only cost a little more compared to buying new guides.
I don't know what causes so much wear so fast, but the exhaust valves are both pretty bad. There really was a good amount of oil in the exhaust ports and it only ran for 15 seconds aside from being kicked over.
There is a good machine shop not far from here and the prices seem reasonable. They seem to do every kind of valve job one can imagine. I may have mine bored with new inserts pressed in. It may only cost a little more compared to buying new guides.
I don't know what causes so much wear so fast, but the exhaust valves are both pretty bad. There really was a good amount of oil in the exhaust ports and it only ran for 15 seconds aside from being kicked over.
If anyone is interested I think I figured out why my valve guides are so worn. First, the facts:
1. All the valve guides are worn.
2. The exhaust guides are worn significantly more than the intake guides.
3. The bike only has about 11,000 miles on it.
Conclusion: This valve guide wear is cause by overheating which is most likely due to oil starvation at some point in the vehicles history.
Why: Valve guides can be worn by a rocker arm that pushes on it laterally, warped springs, or excessive heat. The first two possibilities can be dismissed because all the guides are worn, and uniformly worn; i.e. both intakes slightly and both exhaust more significantly. The odds that all 4 guides would fail in this manner by chance is not likely. What do we know about heat? Well, the intake valves are constantly cooled by incoming air and fuel, while the exhaust valves are not. Some of the heat in the valves is transferred through the stem and into the guide. The exhaust valves will tend to run hotter and so it makes sense that both exhaust guides would be worn a lot more than the intake guides if heat is the cause.
1. All the valve guides are worn.
2. The exhaust guides are worn significantly more than the intake guides.
3. The bike only has about 11,000 miles on it.
Conclusion: This valve guide wear is cause by overheating which is most likely due to oil starvation at some point in the vehicles history.
Why: Valve guides can be worn by a rocker arm that pushes on it laterally, warped springs, or excessive heat. The first two possibilities can be dismissed because all the guides are worn, and uniformly worn; i.e. both intakes slightly and both exhaust more significantly. The odds that all 4 guides would fail in this manner by chance is not likely. What do we know about heat? Well, the intake valves are constantly cooled by incoming air and fuel, while the exhaust valves are not. Some of the heat in the valves is transferred through the stem and into the guide. The exhaust valves will tend to run hotter and so it makes sense that both exhaust guides would be worn a lot more than the intake guides if heat is the cause.
also the recommended gap for the stem to valve guide starts wider. this is due to thermal expansion
So the exhaust valves/guides normally have more clearance when cold? I read that the valves should not wiggle at all. The intake side is so minor I would be inclined to ignore it, but the exhaust side play is a little more worrying. Burning a little extra oil doesn't bother me, but I don't want so much coming in that I am fouling my plugs or risking catastrophic failure.
I don't have any experience with this, so I don't know how much play is "bad" and how much is "acceptable" when considering what I hope to get out of this machine right now.
I don't have any experience with this, so I don't know how much play is "bad" and how much is "acceptable" when considering what I hope to get out of this machine right now.
inlet clearance = 0.010 - 0.037mm
exhaust clearance = 0.030 - 0.057mm
exhaust clearance = 0.030 - 0.057mm
Have you ever tried wiggling them when they are cold? I am also working in a cold environment and I wonder if this is exaggerating the problem since I was kicking it over cold at near-freezing temperatures.
