WTF Interference BP4W - 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 06-05-2015, 09:35 PM   #1
Ben
Supporting Vendor
Thread Starter
iTrader: (33)
 
Ben's Avatar
 
Join Date: Jul 2006
Location: atlanta-ish
Posts: 12,689
Total Cats: 99
Default WTF Interference BP4W

60K mile 99 BP4W longblock, I got it from a 3rd party, who got it from LKQ. "It's a great runner," he said. It was delivered to me without cam pulleys and damper. We replaced the various seals and gaskets, water pump, and go to put a new timing belt on it.

When a cylinder is at TDC, I am unable to rotate the exhaust cam to open exhaust valves. I get a hard stop when the lobes begin pushing lifters. If I take the crank a few degrees off TDC, I can rotate the cams without problem.

Engine appears to be untouched externally, IE not clean, intake and exhaust ports not machined, no aftermarket parts. Junkyard markings on oil pan. Pistons appear to be standard 99 pistons when looking through the plug hole with a flashlight. Unfortunately the bore scope is in the race trailer... in Ohio.

With OEM pistons, can you deck the head enough to create an interference motor?
Ben is offline   Reply With Quote
Old 06-05-2015, 11:12 PM   #2
Goin Innnnn!!!
iTrader: (7)
 
Chooofoojoo's Avatar
 
Join Date: May 2014
Location: Denver, Co.
Posts: 460
Total Cats: 40
Default

Theoretically I think so.

One way to see if it's been decked a lot is to look at these little discs on the bottom of the head (still visible with head installed). If they're machined at all then the head has been shaved a LOT.


Attached Thumbnails
WTF Interference BP4W-80-wp_20140926_009_zps221e73f4_c00766e087e241f11f052e83e12b9014c5ea34cd.jpg  
Chooofoojoo is offline   Reply With Quote
Old 06-10-2015, 01:33 AM   #3
Boosting since 1984
iTrader: (1)
 
stefanst's Avatar
 
Join Date: Sep 2011
Location: Levittown
Posts: 1,198
Total Cats: 68
Default

Might a bent valve hit a piston?
stefanst is offline   Reply With Quote
Old 06-10-2015, 01:56 AM   #4
Junior Member
iTrader: (6)
 
Join Date: Feb 2011
Posts: 422
Total Cats: 9
Default

The head would need over sized valves to do this or the head would have to have been decked probably around 20 thou or more.

take a peek down the ports with the valves open and see if you see stainless valves.
Twibs415 is offline   Reply With Quote
Old 06-10-2015, 02:30 AM   #5
Cpt. Slow
iTrader: (25)
 
curly's Avatar
 
Join Date: Oct 2005
Location: Oregon City, OR
Posts: 12,110
Total Cats: 518
Default

Did it with a vvt motor, think I took .060" off.
curly is offline   Reply With Quote
Old 06-10-2015, 10:38 AM   #6
Elite Member
iTrader: (5)
 
m2cupcar's Avatar
 
Join Date: Jan 2005
Location: Atlanta
Posts: 7,244
Total Cats: 291
Default

That's exactly how we ran 10.25:1 static compression (max allowed by rules) on a 99 after they took away our 10.25:1 pistons, but failed to change the compression figure.
m2cupcar is offline   Reply With Quote
Old 06-13-2015, 09:07 AM   #7
Senior Member
 
Join Date: Apr 2011
Location: Hollywood, FL
Posts: 525
Total Cats: 18
Default

Stupid thought but what if the valves are touching each other? Rotate the other way maybe? Or pull exhaust cam and reinstall close to TDC.
hector is offline   Reply With Quote
Old 04-05-2016, 08:38 PM   #8
Ben
Supporting Vendor
Thread Starter
iTrader: (33)
 
Ben's Avatar
 
Join Date: Jul 2006
Location: atlanta-ish
Posts: 12,689
Total Cats: 99
Default

Had the same result on a different BP4W: Exhaust valves have interference with piston at TDC.

I understand the common wisdom is that these are non interference engines... I'm thinking that ended with the BP4W.
Ben is offline   Reply With Quote
Old 04-05-2016, 09:12 PM   #9
Elite Member
iTrader: (5)
 
Join Date: Oct 2007
Location: Canton, Ga
Posts: 1,707
Total Cats: 19
Default

I have personally wrecked valves in a stock BP4W due to interference. Teardown revealed timing belt was installed improperly, but still...
Stealth97 is offline   Reply With Quote
Old 04-06-2016, 01:33 AM   #10
Senior Member
 
Join Date: Jun 2015
Location: TAMPA, FL
Posts: 644
Total Cats: 27
Default

Is this just an issue with high compression pistons? I thought I was safe with 8.6:1, even with a slightly milled head.
AlwaysBroken is offline   Reply With Quote
Old 04-06-2016, 01:46 AM   #11
Elite Member
iTrader: (15)
 
patsmx5's Avatar
 
Join Date: Aug 2007
Location: Houston, TX
Posts: 8,797
Total Cats: 248
Default

Quote:
Originally Posted by Ben View Post
Had the same result on a different BP4W: Exhaust valves have interference with piston at TDC.

I understand the common wisdom is that these are non interference engines... I'm thinking that ended with the BP4W.
My last two engines both had exhaust valve interference.

First was VVT head with +1mm exhaust valves, with VVT pistons, 0.015" shaved off head.

Second was same head with FM 9:1 pistons, they too hit piston at TDC with max lift on exhaust valves.

Haven't tested a 100% stock motor, but both of mine are interference.
patsmx5 is offline   Reply With Quote
Old 04-06-2016, 11:51 AM   #12
Goin Innnnn!!!
iTrader: (7)
 
Chooofoojoo's Avatar
 
Join Date: May 2014
Location: Denver, Co.
Posts: 460
Total Cats: 40
Default

My 97 block / BP4W head is interference. (BP5a intake cam)
+1 valves intake/exhaust.
They will hit each other, as well as the piston at TDC.

Head is shaved .020".

If this motor was non-interference when stock, it was only so by a kitty-hair.
Chooofoojoo is offline   Reply With Quote
Old 04-06-2016, 11:53 AM   #13
y8s
2 Props,3 Dildos,& 1 Cat
iTrader: (8)
 
y8s's Avatar
 
Join Date: Jun 2005
Location: Fake Virginia
Posts: 19,038
Total Cats: 407
Default

stretched rods from an over-rev?
y8s is offline   Reply With Quote
Old 04-06-2016, 12:00 PM   #14
Ben
Supporting Vendor
Thread Starter
iTrader: (33)
 
Ben's Avatar
 
Join Date: Jul 2006
Location: atlanta-ish
Posts: 12,689
Total Cats: 99
Default

Quote:
Originally Posted by y8s View Post
stretched rods from an over-rev?
Nope.
Ben is offline   Reply With Quote
Old 04-06-2016, 11:55 PM   #15
Junior Member
 
guttedmiata's Avatar
 
Join Date: Sep 2012
Posts: 438
Total Cats: -3
Default

I have 11.5:1 Pistons, oversized valves, and slightly more cam lobe height than stock and there is only interference if I dial the cams too far off of straight up. My guess is you did not get the gears on the cams properly.
guttedmiata is offline   Reply With Quote
Old 04-07-2016, 11:05 AM   #16
Ben
Supporting Vendor
Thread Starter
iTrader: (33)
 
Ben's Avatar
 
Join Date: Jul 2006
Location: atlanta-ish
Posts: 12,689
Total Cats: 99
Default

Quote:
Originally Posted by guttedmiata View Post
I have 11.5:1 Pistons, oversized valves, and slightly more cam lobe height than stock and there is only interference if I dial the cams too far off of straight up. My guess is you did not get the gears on the cams properly.
Bad guess.
Ben is offline   Reply With Quote
Old 04-07-2016, 01:16 PM   #17
Supporting Vendor
iTrader: (31)
 
Savington's Avatar
 
Join Date: Nov 2006
Location: Sunnyvale, CA
Posts: 14,371
Total Cats: 1,332
Default

Quote:
Originally Posted by guttedmiata View Post
I have 11.5:1 Pistons, oversized valves, and slightly more cam lobe height than stock and there is only interference if I dial the cams too far off of straight up. My guess is you did not get the gears on the cams properly.
You lack an understanding of what is actually being discussing here. Cam gear orientation has absolutely no effect on whether an engine is interference or non-interference. Re-read the thread
Savington is offline   Reply With Quote
Old 04-07-2016, 03:25 PM   #18
Senior Member
 
Join Date: Jun 2015
Location: TAMPA, FL
Posts: 644
Total Cats: 27
Default

Quote:
Originally Posted by guttedmiata View Post
I have 11.5:1 Pistons, oversized valves, and slightly more cam lobe height than stock and there is only interference if I dial the cams too far off of straight up. My guess is you did not get the gears on the cams properly.
It's only non-interference if it stays that way when the belt snaps, leaving the valves extended and the pistons still moving.

A 100 dollar belt replacement is a lot less of a hassle than the kind that requires a new piston, new valves and about 100x more labor.
AlwaysBroken is offline   Reply With Quote
Old 04-07-2016, 04:40 PM   #19
Junior Member
iTrader: (6)
 
Join Date: Feb 2011
Posts: 422
Total Cats: 9
Default

So why are we breaking timing belts and not keeping up with regular maintenance?
Twibs415 is offline   Reply With Quote
Old 04-07-2016, 04:47 PM   #20
Ben
Supporting Vendor
Thread Starter
iTrader: (33)
 
Ben's Avatar
 
Join Date: Jul 2006
Location: atlanta-ish
Posts: 12,689
Total Cats: 99
Default

Quote:
Originally Posted by Twibs415 View Post
So why are we breaking timing belts and not keeping up with regular maintenance?
We're not, or at least I'm not. I made some observations when assembling engines that are contrary to popular wisdom, so I posted what I found. My assertion is that BP4W is an interference engine.

The only change to my life is I'm going with the Gates kevlar belts on my NB engines.
Ben is offline   Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
Need help - Stock Balancer and Fastforward overlay pulleys Frank_and_Beans Supercharger Discussion 13 09-12-2016 09:17 PM
elesjuan's mediocre 95 Miata adventure (google fiber edition) elesjuan Build Threads 8 02-16-2016 09:36 PM
DIYPNP problem PA0 VICS output spidy MEGAsquirt 7 09-24-2015 04:14 PM
1.8, C30-74 Rotrex, 9psi, 235WHP/190WTQ (E85) Lincoln Logs Dynos and timesheets 4 09-23-2015 01:26 PM
New personal best 1/8th mile tehzack Dynos and timesheets 10 09-21-2015 07:30 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 03:46 PM.