bengxe

The exhaust valves are from ebay, but the intakes are original and its leaking from both sides.

bengxe

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.

NA6C-Guy

iTrader: (1)

Why would they be bent? I assume you did something bad?

bengxe

I assembled the lifters wrong, making them overextend the valves. Then when I cranked it valves touched pistons. Thats what Im assuming happened.

NA6C-Guy

iTrader: (1)

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.

magnamx-5

iTrader: (7)

um there is no way to bend a valve on a miata unless the **** is way extended we have a non interference engine.

NA6C-Guy

iTrader: (1)

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?

neogenesis2004

iTrader: (12)

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.

NA6C-Guy

iTrader: (1)

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.

saedrin

iTrader: (2)

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.

NA6C-Guy

iTrader: (1)

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.

saedrin

iTrader: (2)

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.

JasonC SBB

Can't believe nobody has spotted this yet. Looking at the lobes of cyl #1, the cam timing is wrong!

bengxe

How so? Where should they be?

hustler

iTrader: (6)

I've seen it done in an accidental 8500rpm over-rev / missed shift.

sixshooter

iTrader: (12)

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.

hustler

iTrader: (6)

If its off in that pic, its just a tooth off on the exhaust. Remember, 19-teeth between the cogs contacting the belt. He also could have swapped or have the gears out 1/3rd. The lobes look fine in that pic to me.

NA6C-Guy

iTrader: (1)

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.

hustler

iTrader: (6)

um...no. The crank turns 2x the cam speed. TDC is top of the compression stroke.

sixshooter

iTrader: (12)

Yeah, I got that part but I think that the letter "I" should be at the four o'clock position on the intake side and the letter "E" should be at the eight o'clock position on the exhaust gear. I was trying to remember and I think he may have them backwards.