Engine rebuild, now no compression
I just finished reassembling my 1.6. Ive done:
new rings rehoned the cylinders new bearings new oem type valve springs (beck arnley) new supertech exhaust valves cleaned off the original intake valves valve seals disassembled the lifters, cleaned and reassembled timing belt head gasket various other seals and gaskets It cranks fast as if theres no compression, and my compression gauge reads zero on all cylinders. Compressed air hooked up to the cylinder 1 plug hole seems to blow out the intake and exhaust, nothing up through the crankcase or out the dipstick tube. I believe its timed right. The marks all line up, the pins on the cams are pointed up and I verified cyinder 1 tdc with a screwdriver down the spark plug hole. The cams dont appear to press the cylinder 1 lifters down at cylinder 1 tdc, so my next thought was that I reassembled the lifters with too much oil in them, causing them to overextend. I took them out and drained and recleaned them, reinstalled with no oil in them. Same problem. I believe I seated the valves completely, but this is my first time getting into the internals of an engine. Im running out of ideas now, so any insight would really be appreciated. |
I would double check that it is timed right. Maybe take pictures of the gears and show us.
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did you lap the valves?
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My guess is that your timing is way off.
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either way off cam timming or your valves are flaoting in space and not sealing the combustion chamber before you take off the head. i would check the timming agian, and if it is 1000000000000000000% correct then i would be inclined to pull the came and or allow the valves to enter there fully closed position with no laod holding them open whatsoever and perform a leak down test if this does not go well then you need to pull the head and possibly the motor and get to the botom of this.
If this does work, obviusly something is binding your valves open or they are to long for some unknown reason to seat properly. |
Tomorrow I will quadruple check my timing, and post pictures here. I hope you guys are right and it is a timing issue. Hustler, Im assuming lapping valves = seating valves, and yes I did. Im not entirely sure I did it the right way, but I ground the valves into the seats til there was about a 1mm mating surface all around. It looked to me like the valves would have no problem sealing. But I think Ill pull both manifolds off tomorrow to try to look at the valves. Thanks for all the help so far.
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Originally Posted by magnamx-5
(Post 451984)
either way off cam timming or your valves are flaoting in space and not sealing the combustion chamber before you take off the head. i would check the timming agian, and if it is 1000000000000000000% correct then i would be inclined to pull the came and or allow the valves to enter there fully closed position with no laod holding them open whatsoever and perform a leak down test if this does not go well then you need to pull the head and possibly the motor and get to the botom of this.
If this does work, obviusly something is binding your valves open or they are to long for some unknown reason to seat properly. |
Originally Posted by bengxe
(Post 451988)
I did pull the cams and blow air into cylinder 1, I did here some air blowing out the intake and exhaust but it was less than with the cams on. I dont know if this is normal. Im not sure what exactly a leakdown test entails, and I dont have access to a leakdown tester.
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Thats exactly what I was afraid of, and what most people told me to do in the first place. Now Im wondering at what point do I cut my losses and find a low mileage 1.8.
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Make sure your cams are oriented correctly. Perfect timing doesn't help when there are valves open at TDC.
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Originally Posted by bengxe
(Post 451996)
Thats exactly what I was afraid of, and what most people told me to do in the first place. Now Im wondering at what point do I cut my losses and find a low mileage 1.8.
And save his stuff isnt sealing with the cams off ie valves should be 100% closed this tells us something is done wrong somewhere. |
Another vote here for check the timing. Even if the rings didn't seat well and the valve seats are leaky, it would still show something on the gauge.
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http://i65.photobucket.com/albums/h2...e/S5000631.jpg
http://i65.photobucket.com/albums/h2...e/S5000632.jpg Heres my timing marks. I couldnt get a picture of the crank pulley to turn out well enough to be useful, but I found tdc with a screwdriver down the plug hole and then verified it with the notch on the crank timing belt cog. http://i65.photobucket.com/albums/h2...e/S5000635.jpg This is what my cams look like at cylinder 1 tdc. I pulled the exhaust off to look at the back side of the valves, but didnt see anything wrong (couldnt see much). Tomorrow Ill pull the head. |
If you still have the cams out, you could put each cylinder at tdc and shine a bright flashlight into the plug hole. If the valves are not sealing you will be able to see light when looking through the intake and/or exhaust ports for that cylinder.
I'm also wondering if something happened to your lifters when you took them apart. Possible that they are not depressurizing at all and are actually lifting too high. You should be able to squeeze them by hand. |
Not that it's in any way related to your compression problem, but:
http://img40.imagefra.me/img/img40/2...lm_114be2b.png |
Good catch, that sucker is on backwards. I hope those things are in the correct order. That picture does not leave me with a feeling that they are.
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:werd: ^ you better swap that around before you get some aluminum dust floating around your engine.
I've seen a head that had the valves cut one too many times- they wouldn't seat. |
Is it possible the valves are 1.8 valves? Larger head and longer iirc.
Ron |
Originally Posted by Joe Perez
(Post 452408)
Not that it's in any way related to your compression problem, but:
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Originally Posted by neogenesis2004
(Post 452406)
I'm also wondering if something happened to your lifters when you took them apart. Possible that they are not depressurizing at all and are actually lifting too high. You should be able to squeeze them by hand.
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Originally Posted by Alta_Racer
(Post 452446)
Is it possible the valves are 1.8 valves? Larger head and longer iirc.
Ron |
Fixing the lifters gave me compression on 2 and 4, but 1 and 3 still leak out the exhaust. So Im assuming I bent those valves. Im ordering 4 exhaust valves and Im going to try to find time to pull the head this weekend.
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Why would they be bent? I assume you did something bad?
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I assembled the lifters wrong, making them overextend the valves. Then when I cranked it valves touched pistons. Thats what Im assuming happened.
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How did you assemble them wrong? Sucks to hear. If thats the case then that is for sure your problem. Bent valves surely won't hold compression. Just when I thought the Miata's were safe from bending valves. I've had bad luck with bent valves. They do usually come in large numbers in situations like yours. If one goes, so do the rest. Both times I've dealt with them I bent 14 of 16 and 15 of 16.
PS, a lot of aftermarket valves come with longer stems for cams with a smaller base circle. PSS, how do the valve seats look in the head? I know when I did my head, the seats and valves were for sure not going to work if swapped around, or the seats wouldn't have worked with new valves unless I had them machined. Don't know if you took this into account or not. |
um there is no way to bend a valve on a miata unless the shit is way extended we have a non interference engine.
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Good, thought that was the case. What about with an HLA assembled wrong? How much farther would the valve have to go to make contact with a piston?
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Thats a good question. If you put it in tdc a cyl with no comp and did the light test I told you you could get a good visual estimate of the extra distance. I have no idea what amount of additional lift it takes to make our motor have piston to valve contact.
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I would imagine not much. Looking at the head with it off the block with cams at maximum lift, the valves stick out a fair amount past the deck. Pistons at TDC aren't very far below the deck of the block, with the little valve "cups" on the piston face. Couldn't be more than 1/4'', at least I wouldn't think. My head is machined ~.030'' and the block deck another .005'' so I am probably not far from being able to bend valves with some over revving action and valve float.
I would think an HLA that was assembled wrong and is locked up would possibly cause contact. |
If you want I can test this tomorrow with my spare BP4W head sitting in my garage. I can tell you that even though the engine is non-interference it's a close fit.
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If you would. I'm curious to know. Like I said, I recall that the bottom edge of the valve stuck past the deck of the head by probably 1/4'', and the pistons aren't that far below the deck of the block. It can't be much at all.
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I'll try to measure the distance between the TDC on the piston and the deck and the protrusion of the valves. I mean it's possible you could have messed the valving up a bit but the only thing I can think of that would change valve height is cam profile and valve spring size.
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Originally Posted by bengxe
(Post 452343)
http://i65.photobucket.com/albums/h2...e/S5000635.jpg
This is what my cams look like at cylinder 1 tdc. |
How so? Where should they be?
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Originally Posted by magnamx-5
(Post 452740)
um there is no way to bend a valve on a miata unless the shit is way extended we have a non interference engine.
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Originally Posted by JasonC SBB
(Post 452859)
Can't believe nobody has spotted this yet. Looking at the lobes of cyl #1, the cam timing is wrong!
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Originally Posted by sixshooter
(Post 452891)
I thought he had the E and the I backwards (on the cam gears), but it's been several months since I did my timing belt replacement.
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Its been nearly a year for me since doing a timing belt, but from what I remember it looks correct. Or is that 180* out of time? Stupid of me to not know, but doesn't the crank turn clockwise? Been a while since I looked at the engine honestly. If it does turn CW, doesn't that mean the exhaust valve will be open on the down stroke, and intake open on the up stroke? Lobed would need to point inward. Unless it rotated CCW, in which case that is correct.
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Originally Posted by NA6C-Guy
(Post 452963)
If it does turn CW, doesn't that mean the exhaust valve will be open on the down stroke, and intake open on the up stroke? Lobed would need to point inward. Unless it rotated CCW, in which case that is correct.
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1 Attachment(s)
Originally Posted by hustler
(Post 452904)
If its off in that pic, its just a tooth off on the exhaust. Remember, 19-teeth between the cogs contacting the belt.
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Originally Posted by hustler
(Post 452971)
um...no. The crank turns 2x the cam speed. TDC is top of the compression stroke.
I think the way he has it is correct. |
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