What to do about scored cam journals? - 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 09-01-2015, 05:18 PM   #1
Boost Pope
Thread Starter
iTrader: (8)
 
Joe Perez's Avatar
 
Join Date: Sep 2005
Location: Delicious and Moist.
Posts: 26,331
Total Cats: 1,928
Default What to do about scored cam journals?

This is a general question. I'm not facing an immediate crisis, just happened to be wondering...

Most engines I've laid hands upon, other than the Mazda B-series, use replaceable camshaft bearings. Our engines, curiously, do not.

The NA and NB are now sufficiently aged that we're already starting to see cylinder heads with considerable wear / scoring to the both the cam journals and the surfaces in the head upon which they ride. And, to the best of my knowledge, none of the B engines of interest to us are still being manufactured. The time will eventually come when tossing "used up" heads into the trash and replacing them starts to become economically unfeasible.

How is this situation generally dealt with? Is there some source of aftermarket cam bearing inserts which can be installed into the head after line-boring?

BogusSVO?
Joe Perez is offline   Reply With Quote
Old 09-01-2015, 05:29 PM   #2
SADFab Destructive Testing Engineer
iTrader: (5)
 
aidandj's Avatar
 
Join Date: Apr 2014
Location: Beaverton, USA
Posts: 18,000
Total Cats: 1,466
Default

<p>
Quote:
Originally Posted by Joe Perez View Post
Is there some source of aftermarket cam bearing inserts which can be installed into the head after line-boring?
</p><p>That sounds really expensive.</p>
aidandj is offline   Reply With Quote
Old 09-01-2015, 05:30 PM   #3
Elite Member
iTrader: (3)
 
Join Date: Mar 2008
Location: Granbury, TX
Posts: 6,012
Total Cats: 584
Default

I recently had a head rebuilt and the machine shop media blasted it but did a poor job of cleaning the oil galley. The end result was grit and scoring of the cam journals and the steel bearing surface of the cam.

We replaced the camshaft (gouges too deep to polish) and the head was line bored and bearings installed. The reassembled engine ran fine on track. I eventually replaced the head in question with a low-mileage head from the JY (rebuilt by a different shop). But the take-away is that, yes, you can successfully line bore and install bearings into these heads and have good results.
hornetball is online now   Reply With Quote
Old 09-01-2015, 05:32 PM   #4
Elite Member
iTrader: (3)
 
Join Date: Mar 2008
Location: Granbury, TX
Posts: 6,012
Total Cats: 584
Default

Quote:
Originally Posted by aidandj View Post
<p></p><p>That sounds really expensive.</p>
Maybe now. But it might be the economical (or only possible) option in 2030. 2030 will be here sooner than you think my young friend.
hornetball is online now   Reply With Quote
Old 09-01-2015, 05:42 PM   #5
Senior Member
 
Join Date: Jun 2015
Location: TAMPA, FL
Posts: 646
Total Cats: 27
Default

By that point, I hope there are better options than the BP engine available. There may also be cheaper project car platforms to take the place of the miata by then.

I think most people would be ok walking away from the BP and its headaches for something along the lines of the LFX. The more time goes by, the less and work is involved in replacing the BP engine with something that makes more power out of the box and is lighter weight.

The more expensive BP engines and parts become, the cheaper (relatively speaking) swaps become. Look at how many 60s muscle cars are driving around today with stuff like LSX swaps.
AlwaysBroken is offline   Reply With Quote
Old 09-01-2015, 05:42 PM   #6
Boost Pope
Thread Starter
iTrader: (8)
 
Joe Perez's Avatar
 
Join Date: Sep 2005
Location: Delicious and Moist.
Posts: 26,331
Total Cats: 1,928
Default

Quote:
Originally Posted by hornetball View Post
Maybe now. But it might be the economical (or only possible) option in 2030. 2030 will be here sooner than you think my young friend.
That's exactly my point.

Especially given that 2015 probably seemed like a *REALLY* long way away back in 1990 when Mark Booth first started complaining about how the antenna on the first-gen cars wasn't retractable. A lot of the folks on this forum hadn't even been born then.

When the first VW Beetles started rolling onto US shores in the early 1950s, I doubt that many people were thinking about what parts availability would be like for them 65 years later. But those cars are still on the road. (They also had replaceable camshaft bearings from the factory.)
Joe Perez is offline   Reply With Quote
Old 09-01-2015, 05:44 PM   #7
Boost Pope
Thread Starter
iTrader: (8)
 
Joe Perez's Avatar
 
Join Date: Sep 2005
Location: Delicious and Moist.
Posts: 26,331
Total Cats: 1,928
Default

Quote:
Originally Posted by AlwaysBroken View Post
The more expensive BP engines and parts become, the cheaper (relatively speaking) swaps become.

Look at how many 60s muscle cars are driving around today with stuff like LSX swaps.
Doing a complete drivetrain swap is never, ever, ever going to be easier or more economical than line-boring a block and head.

Dropping a Chevy V8 into a car that originally came with a Chevy V8 isn't quite the same thing as what you're proposing.
Joe Perez is offline   Reply With Quote
Old 09-01-2015, 05:59 PM   #8
Elite Member
iTrader: (8)
 
bahurd's Avatar
 
Join Date: Apr 2013
Location: Ohio
Posts: 2,132
Total Cats: 145
Default

<p>
Quote:
Originally Posted by Joe Perez View Post
</p><p>Most engines I've laid hands upon, other than the Mazda B-series, use replaceable camshaft bearings. Our engines, curiously, do not.</p><p>BogusSVO?
</p><p>I've been pretty involved with the startup of numerous engine lines (multiple OEMs) over the past decade.&nbsp; All of the OHC variants use the same basic design.&nbsp; Bolt caps on + bore with a tool constructed with guide pads to &quot;line bore&quot; the cam bores + remove caps on an automated line just prior to insertion of the cams.&nbsp;</p><p>The OEMs do it because a. they can achieve the quality and b. it's less expensive to do.</p><p>Knowing the quality of the original mfg line I always question if a shop can achieve the same thing.&nbsp; I did have an opportunity to sell tooling to a guy who bought original castings for the Ford 427 SOHC heads that he intended to sell in the aftermarket.&nbsp; I guess there's always a way if there's a market.</p><p>&nbsp;</p><p>&nbsp;</p>
bahurd is offline   Reply With Quote
Old 09-01-2015, 06:36 PM   #9
Senior Member
 
Join Date: Jun 2015
Location: TAMPA, FL
Posts: 646
Total Cats: 27
Default

One thing I always wondered was why aftermarket chevy heads are a dime a dozen but nothing has been available at non-insane prices for even commonly used 4 bangers... is it purely a matter of market size or is it also the greater cost of slapping together an OHC engine vs a set of pushrod heads.
AlwaysBroken is offline   Reply With Quote
Old 09-01-2015, 06:38 PM   #10
SADFab Destructive Testing Engineer
iTrader: (5)
 
aidandj's Avatar
 
Join Date: Apr 2014
Location: Beaverton, USA
Posts: 18,000
Total Cats: 1,466
Default

<p>Market size.</p><p>There is an unbelievable number of those things out there.</p><p>Didn't the chevy small block have a 50+ year production run. In a whole **** ton of cars.</p>
aidandj is offline   Reply With Quote
Old 09-01-2015, 06:48 PM   #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 Joe Perez View Post
How is this situation generally dealt with? Is there some source of aftermarket cam bearing inserts which can be installed into the head after line-boring?
A machine shop can micropolish the cam journals to remove any high spots from them. If the journals are trashed, they can machine them down to a smaller diameter (example, 36mm to 35mm diameter).

For the head, if only 1 bearing was damaged, the easy way to fix it is to simply debur it/remove the high spot. The expensive way is to skim the caps and line bore the caps again.

In my experience since the cams are steel and the bearings are aluminum, the cams are always fine, and the aluminum head takes the damage since it's the softer metal. I trashed a bearing on my VVT head a while back running the engine without oil until the intake cam seized up, and was able to repair that journal with a Dremel and patience. Now where the "missing metal" is, gets filled in with oil since these are pressure lubricated. I've even torn it apart twice to inspect, there is no visible wear since the repair, and I run stiff valve springs and high RPMs, so not babying it either. Would have been better to skim the caps in my case, but I didn't want to pull the head at the time, and now that the repair has held up, I'll probably just keep running it.
patsmx5 is offline   Reply With Quote
Old 09-01-2015, 09:42 PM   #12
Elite Member
iTrader: (8)
 
bahurd's Avatar
 
Join Date: Apr 2013
Location: Ohio
Posts: 2,132
Total Cats: 145
Default

<p>
Quote:
Originally Posted by AlwaysBroken View Post
One thing I always wondered was why aftermarket chevy heads are a dime a dozen but nothing has been available at non-insane prices for even commonly used 4 bangers... is it purely a matter of market size or is it also the greater cost of slapping together an OHC engine vs a set of pushrod heads.
</p><p>Aftermarket is a different story but the cost to produce a cylinder head today, at an OEM and assuming a DOHC 4 cyl variant, compared to a 4cyl cam in block head of 2 decades ago is at least 4X.&nbsp; Quality costs money.&nbsp; Roundness of a DOHC cam bore today is 0.025mm (B/P tolerance) not to mention straightness of the bores to each other.&nbsp; Valve seats are a powdered metal close to Stellite in composition whereas some of the old CI heads didn't even have separate seats and if they did were of a easy to machine alloy.&nbsp; Seat ovality is within 0.015mm (Process tolerance) and @ a tool change is typically 0.004mm or under.&nbsp; Seat to guide is similarly close and the process is pretty costly because 1. of the process I.E. CNC modular machines with tool changers vs the old Transfer Lines with dedicated stations and 2. tooling cost of perishables.</p><p>Pushrod bores were cast in place.&nbsp; Bucket bores in a DOHC head are all machined.</p><p>&nbsp;</p>
bahurd is offline   Reply With Quote
Old 09-01-2015, 11:16 PM   #13
Elite Member
iTrader: (2)
 
Join Date: Dec 2011
Posts: 1,517
Total Cats: 142
Default

Quote:
Originally Posted by Joe Perez View Post
...

back in 1990 when Mark Booth first started complaining about how the antenna on the first-gen cars wasn't retractable. ...
I almost lost a mouthful of beer on that one Joe.
good2go 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 12-15-2017 09:00 PM
Toyota Pickup Engine Swap B.S. Monk Build Threads 24 12-11-2016 03:21 PM
High-lift cams, SUB, new valve job = lifter tick? Der_Idiot Engine Performance 14 09-16-2015 10:30 PM
Dumb question about crank and cam angle sensors AlwaysBroken Engine Performance 4 09-04-2015 02:35 PM
Maruha 10mm lift cams + Supertech SUB; lifter edge wear? Der_Idiot Engine Performance 12 09-03-2015 04:31 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 06:45 PM.