Engine rebuild, now no compression - Page 2 - Miata Turbo Forum - Boost cars, acquire cats.

Welcome to Miataturbo.net   Members
 


Engine Performance This section is for discussion on all engine building related questions.
Sponsored by:
Sponsored by:

Reply
 
 
 
LinkBack Thread Tools Search this Thread
Old 09-10-2009, 02:34 PM   #21
Newb
Thread Starter
 
Join Date: Jan 2008
Location: Baltimore County, MD
Posts: 27
Total Cats: 0
Default

Quote:
Originally Posted by Alta_Racer View Post
Is it possible the valves are 1.8 valves? Larger head and longer iirc.

Ron
The exhaust valves are from ebay, but the intakes are original and its leaking from both sides.
bengxe is offline   Reply With Quote
Old 09-10-2009, 10:18 PM   #22
Newb
Thread Starter
 
Join Date: Jan 2008
Location: Baltimore County, MD
Posts: 27
Total Cats: 0
Default

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.
bengxe is offline   Reply With Quote
Old 09-10-2009, 11:18 PM   #23
Elite Member
iTrader: (1)
 
NA6C-Guy's Avatar
 
Join Date: Feb 2008
Location: Birmingham Alabama
Posts: 8,038
Total Cats: 43
Default

Why would they be bent? I assume you did something bad?
NA6C-Guy is offline   Reply With Quote
Old 09-10-2009, 11:37 PM   #24
Newb
Thread Starter
 
Join Date: Jan 2008
Location: Baltimore County, MD
Posts: 27
Total Cats: 0
Default

I assembled the lifters wrong, making them overextend the valves. Then when I cranked it valves touched pistons. Thats what Im assuming happened.
bengxe is offline   Reply With Quote
Old 09-11-2009, 12:05 AM   #25
Elite Member
iTrader: (1)
 
NA6C-Guy's Avatar
 
Join Date: Feb 2008
Location: Birmingham Alabama
Posts: 8,038
Total Cats: 43
Default

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.
NA6C-Guy is offline   Reply With Quote
Old 09-11-2009, 01:12 AM   #26
:(
iTrader: (7)
 
Join Date: Jul 2006
Location: nowhere
Posts: 8,281
Total Cats: 2
Default

um there is no way to bend a valve on a miata unless the **** is way extended we have a non interference engine.
magnamx-5 is offline   Reply With Quote
Old 09-11-2009, 01:17 AM   #27
Elite Member
iTrader: (1)
 
NA6C-Guy's Avatar
 
Join Date: Feb 2008
Location: Birmingham Alabama
Posts: 8,038
Total Cats: 43
Default

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?
NA6C-Guy is offline   Reply With Quote
Old 09-11-2009, 01:19 AM   #28
Elite Member
iTrader: (12)
 
Join Date: Aug 2006
Location: Central-ish VA
Posts: 4,449
Total Cats: 16
Default

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.
neogenesis2004 is offline   Reply With Quote
Old 09-11-2009, 01:27 AM   #29
Elite Member
iTrader: (1)
 
NA6C-Guy's Avatar
 
Join Date: Feb 2008
Location: Birmingham Alabama
Posts: 8,038
Total Cats: 43
Default

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.
NA6C-Guy is offline   Reply With Quote
Old 09-11-2009, 02:06 AM   #30
Junior Member
iTrader: (2)
 
Join Date: Sep 2009
Location: Chicago, IL
Posts: 250
Total Cats: 0
Default

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.
saedrin is offline   Reply With Quote
Old 09-11-2009, 02:28 AM   #31
Elite Member
iTrader: (1)
 
NA6C-Guy's Avatar
 
Join Date: Feb 2008
Location: Birmingham Alabama
Posts: 8,038
Total Cats: 43
Default

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.
NA6C-Guy is offline   Reply With Quote
Old 09-11-2009, 02:32 AM   #32
Junior Member
iTrader: (2)
 
Join Date: Sep 2009
Location: Chicago, IL
Posts: 250
Total Cats: 0
Default

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.
saedrin is offline   Reply With Quote
Old 09-11-2009, 11:30 AM   #33
Elite Member
 
Join Date: Jul 2005
Posts: 6,454
Total Cats: 80
Default

Quote:
Originally Posted by bengxe View Post

This is what my cams look like at cylinder 1 tdc.
Can't believe nobody has spotted this yet. Looking at the lobes of cyl #1, the cam timing is wrong!
JasonC SBB is offline   Reply With Quote
Old 09-11-2009, 12:10 PM   #34
Newb
Thread Starter
 
Join Date: Jan 2008
Location: Baltimore County, MD
Posts: 27
Total Cats: 0
Default

How so? Where should they be?
bengxe is offline   Reply With Quote
Old 09-11-2009, 12:30 PM   #35
Tour de Franzia
iTrader: (6)
 
hustler's Avatar
 
Join Date: Jun 2006
Location: Republic of Dallas
Posts: 29,114
Total Cats: 351
Default

Quote:
Originally Posted by magnamx-5 View Post
um there is no way to bend a valve on a miata unless the **** is way extended we have a non interference engine.
I've seen it done in an accidental 8500rpm over-rev / missed shift.
hustler is offline   Reply With Quote
Old 09-11-2009, 12:52 PM   #36
Moderator
iTrader: (11)
 
sixshooter's Avatar
 
Join Date: Nov 2008
Location: Tampa, Florida
Posts: 15,680
Total Cats: 1,561
Default

Quote:
Originally Posted by JasonC SBB View Post
Can't believe nobody has spotted this yet. Looking at the lobes of cyl #1, the cam timing is wrong!
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.
sixshooter is offline   Reply With Quote
Old 09-11-2009, 01:24 PM   #37
Tour de Franzia
iTrader: (6)
 
hustler's Avatar
 
Join Date: Jun 2006
Location: Republic of Dallas
Posts: 29,114
Total Cats: 351
Default

Quote:
Originally Posted by sixshooter View Post
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.
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.
hustler is offline   Reply With Quote
Old 09-11-2009, 03:51 PM   #38
Elite Member
iTrader: (1)
 
NA6C-Guy's Avatar
 
Join Date: Feb 2008
Location: Birmingham Alabama
Posts: 8,038
Total Cats: 43
Default

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.
NA6C-Guy is offline   Reply With Quote
Old 09-11-2009, 04:05 PM   #39
Tour de Franzia
iTrader: (6)
 
hustler's Avatar
 
Join Date: Jun 2006
Location: Republic of Dallas
Posts: 29,114
Total Cats: 351
Default

Quote:
Originally Posted by NA6C-Guy View Post
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.
um...no. The crank turns 2x the cam speed. TDC is top of the compression stroke.
hustler is offline   Reply With Quote
Old 09-11-2009, 05:27 PM   #40
Moderator
iTrader: (11)
 
sixshooter's Avatar
 
Join Date: Nov 2008
Location: Tampa, Florida
Posts: 15,680
Total Cats: 1,561
Default

Quote:
Originally Posted by hustler View Post
If its off in that pic, its just a tooth off on the exhaust. Remember, 19-teeth between the cogs contacting the belt.
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.
Attached Thumbnails
Engine rebuild, now no compression-s5000631.jpg  
sixshooter is offline   Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
Project Gemini - Turbo Civic on the Cheap Full_Tilt_Boogie Build Threads 59 Yesterday 09:00 PM
1994 Spec Miata Race Car SM/SM2/SSM For Sale Quinn Cars for sale/trade 6 10-23-2016 08:58 AM
Changing from 460cc to flow force 610cc in diypnp 90 Turbo MEGAsquirt 19 10-19-2015 04:23 PM
Expected intake temps on the track? tazswing Race Prep 20 10-03-2015 12:04 PM
3rd Time's a Charm...hopefully. zephyrusaurai Meet and Greet 2 09-28-2015 11:59 PM


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -4. The time now is 11:08 AM.