Out of my 7 cars, 3 of my side skins are cracked. 3 of the skins were in good condition several years ago and have not been damaged while cars were in storage. I ran the math and Honda made an interference error in the tolerance stack up. I've seen this issue on alot of other TX cars (thinking southern cars are more UV degraded and the plastic just can't hold anymore and pops. Obviously colder in North, so more stress, but don't hear about this as much up there.)
During winter cold temperatures, the plastic shrinks faster than the metal. The lips on the edges of the skin constrain the plastic around the metal door, has no where to go and it cracks.
I know this to be true for 86/87 model years, but don't have direct proof for 84/85 yet.
I put this summary together for the Q&A section for our website. Please review and give inputs before I figure out how to input to the site.
Purpose of this is to encourage all of you to begin acquiring these parts in the junkyards ASAP. I recently did an upper midwest parts trip and picked up a decent supply to keep my fleet going. Got most for $20-30. So get them now. Several guys are trying to get $100 per unit on these. Help your fellow RPR'r.
I'm not exactly sure on the difference in the 84 garnish (p/n ending -010ZZ). The 86/87 p/n ends in -970ZZ.
1
Crx Design Flaw: Door Side Skins (plastic)
Started by greasemonkeyreborne 5x1g's, Sep 20 2009 10:30 AM
26 replies to this topic
#1
Posted 20 September 2009 - 10:30 AM
#2
Posted 20 September 2009 - 10:39 AM
The difference is the 86/87 door skins have provisions to work with the Si style bump strips, while the 84/85 only work with the HF/DX style bumpstrips.
#3
Posted 20 September 2009 - 09:20 PM
I have an 86 Si that has a small crack at the bottom of the door panel.
#4
Posted 20 September 2009 - 09:26 PM
all i have is sunfaded, red panel that is now is pink in color, no cracks or other wear, nice pamphlet info there
#5
Posted 20 September 2009 - 09:52 PM
Eh when I paint mine it's gonna get plastic epoxy anyway, so it can crack all it wants I'm just gonna keep putting more on hah.
#6
Posted 21 September 2009 - 01:57 PM
#7
Posted 21 September 2009 - 08:31 PM
I need to take some pictures of the cracks and add them to the Power point slides for better clarification. If you think somethink is not explained enough, please pipe up so I can improve this.
I was interesting, when I looked at the black straman here in Dallas last month, I notice one skin just beginning to crack from top to bottom. It hadn't cracked all the way through yet. The owner Said she just washed the car recently and it wasn't there. So it just began cracking recently.
Crack began at top. Makes sence b/c the widest point in the door is just behind the protection molding (and the least amount of clearance = most interference and most stress= pop.
I see this to be an issue for those of us who plan on keeping the cars for the next 20yrs. Constant cycling back and forth will eventually break it (like bending a paperclip).
Stock up for the future!
D
I was interesting, when I looked at the black straman here in Dallas last month, I notice one skin just beginning to crack from top to bottom. It hadn't cracked all the way through yet. The owner Said she just washed the car recently and it wasn't there. So it just began cracking recently.
Crack began at top. Makes sence b/c the widest point in the door is just behind the protection molding (and the least amount of clearance = most interference and most stress= pop.
I see this to be an issue for those of us who plan on keeping the cars for the next 20yrs. Constant cycling back and forth will eventually break it (like bending a paperclip).
Stock up for the future!
D
Keepin' it OEM
#8
Posted 21 September 2009 - 09:09 PM
Here's a Pix of a crack right down the middle. No impact evidence, it just popped from being stretch
Here's the beginnings of a crack at the end. This is from the fold in the metal door just behind the protective molding.
Here's the full force end result of the folds in the door pushing through end of the plastic lip. Notice the two deepest points into the part. They line up perfectly w/ the 2 folds in the door. Like a two pronged fork pushing its way through.
Here's the beginnings of a crack at the end. This is from the fold in the metal door just behind the protective molding.
Here's the full force end result of the folds in the door pushing through end of the plastic lip. Notice the two deepest points into the part. They line up perfectly w/ the 2 folds in the door. Like a two pronged fork pushing its way through.
Keepin' it OEM
#9
Posted 21 September 2009 - 09:14 PM
GREAT work.
Andrew just needs to work on recreating these in fiberglass, next, after he has his Si spoiler done. He obviously has the fab skills, and has shown some interest. He just needs some pics of the CRX door skins, as he has never seen one. Ideally, if someone could reproduce them in metal...
Andrew just needs to work on recreating these in fiberglass, next, after he has his Si spoiler done. He obviously has the fab skills, and has shown some interest. He just needs some pics of the CRX door skins, as he has never seen one. Ideally, if someone could reproduce them in metal...
WagoCats HOOOOOOOO!!!!!
#10
Posted 23 September 2009 - 11:20 AM
QUOTE (greasemonkeyreborne 5x1g's @ Sep 21 2009, 10:09 PM) <{POST_SNAPBACK}>
Here's a Pix of a crack right down the middle. No impact evidence, it just popped from being stretch
Here's the beginnings of a crack at the end. This is from the fold in the metal door just behind the protective molding.
Here's the beginnings of a crack at the end. This is from the fold in the metal door just behind the protective molding.
Both of the above on my Driver's side and passenger side has the same crack down the middle. These two panels ar the only thing keeping me out of the paint shop right now. Haven't been able to find anything decent.
QUOTE (cbstdscott @ Mar 4 2010, 10:40 AM) <{POST_SNAPBACK}>
The Rule of Money. Any Money spent on a car project will require a Square Root amount more Money spent to make the original Money's investment worthwhile.
#11
Posted 23 September 2009 - 11:40 AM
One of the MANY flaws in our cars. First being the use of stupid plastic for major panels. Great work exposing how the designers made the cars just good enough to last the minimum to clear warranty repairs. I went and looked at mine luckily they are good (for now).
#12
Posted 23 September 2009 - 11:47 AM
Good info greasemonkey. I repaired my sideskirts and door skins during the restoration. ALL cracks and broken pieces were fixed to look brand new. Liz is garage kept all year and still I have started to see new cracks developing. I have a replacement set that needs slight work and I plan to reinforce the backs with fiberglass this winter.
Adding power makes you faster in the straights. Subtracting weight makes you faster everywhere. - Colin Chapman
#13
Posted 23 September 2009 - 11:52 AM
I think it's more than just a differential expansion problem.
You also have to conider the elasiticity of the plastic when there is interference. That elasticity changes however based on the moisture content of the plastic, the temperature, the amount of UV exposure. Etc Etc.
As a basic study this is good but I wouldn't call it a design flaw. More a design compromise like the ones I have to make every day.
You also have to consider the abuse that panel recieves each and every time the door is closed. The door is hardly infinately stiff and will bend and either stretch or compress this doorskin. Also, that portion at the rearmost tip of the door where it wraps around the hem flange can contact the B pillar structure when the door is closed dependent on the alignment of the door, striker hinges etc.
Sounds like I used to work in automotive design and testing doesn't it?
Like I said, a good basic study but there are FAR more variables than you are considering to make certain judgement that it is a design flaw.
Just my 0.02
Rob
You also have to conider the elasiticity of the plastic when there is interference. That elasticity changes however based on the moisture content of the plastic, the temperature, the amount of UV exposure. Etc Etc.
As a basic study this is good but I wouldn't call it a design flaw. More a design compromise like the ones I have to make every day.
You also have to consider the abuse that panel recieves each and every time the door is closed. The door is hardly infinately stiff and will bend and either stretch or compress this doorskin. Also, that portion at the rearmost tip of the door where it wraps around the hem flange can contact the B pillar structure when the door is closed dependent on the alignment of the door, striker hinges etc.
Sounds like I used to work in automotive design and testing doesn't it?
Like I said, a good basic study but there are FAR more variables than you are considering to make certain judgement that it is a design flaw.
Just my 0.02
Rob
Edited by RETROCRX, 23 September 2009 - 11:54 AM.
Must.....go......racing.......
#14
Posted 23 September 2009 - 01:54 PM
^ I agree with this.. Calling it a design flaw. I would say lack of a better materials. That Tupperware I used for my lunch only lasted a few times in the dishwasher heating and cooling. My metal pots are still great.
But for them to last a good 20 years is great IMO.. Honda probably thought of the CRX as a "throw away car" when it was on the design table.
But for them to last a good 20 years is great IMO.. Honda probably thought of the CRX as a "throw away car" when it was on the design table.
#15
Posted 23 September 2009 - 07:29 PM
Thnx for the feedback on this analysis. Again, need all your opinions/experiences before I figure out how to put this in WIKI. I'm hoping to highlight this so we can collect "good" skins before they go to the crusher.
As a side note: (But that doesn't seem to be in question right now). Fundatmentally, the CTE's are not exact. I pulled the books and picked middle road CTEs for materials. I took a piece of broken fender about 4inches long. Put in it ice water, measured it. Then boiled it, measured it. I got a CTE of .00005, where the book gave ave ABS of .000056. Not bad.
Aggree that road vibration and door slamming will accelerate this. Will note to the pitch
Aggree UV degredation accelerates this. I believe this is noted in the pitch
Aggree modulous of elasticity decreases greatly as temperature drops. Fundamental characteristic in plastics and will add to pitch. Actually, I'll try and find a chart over temp on the strength degredation over temp.
Plastic does absorb moisture. But is not considered in design because test samples are equalized at 50% RH @ 75f for at least 48 hours after they come out the the 180F mold before testing. So the tech data sheets already have moisture content accounted for in the test data for the engineers to design to. Not planning on adding this one. But I like how you think!!
However, to have a .070" interference is a design flaw. Some fundamentals are proper material selection, tolerance stack up analysis (ProE and AutoCAD and do these very well) and function over environmental condtions (in this case temp), chemical exposure.
Maybe you're right and Honda punted and balanced the justified the risk as not life threating. Take a paper clip. Bend it back and forth 5x and it breaks quickly b/c bending in both directions. Take a spring bending in force under one direction and you get thousands of cycles before failure. The skin acts like a one dimentional spring due to the interference and eventually gets stretched in one direct every diaurnal day there's interfence. That may not have been a big deal to Honda, but I find it hard to chew when so many other features of the car are so well designed for long term reliability. The plastics industry really blossomed in the 1980's. I didn't joint until 1991 with the Saturn door panel program. They really pushed the limits w/ car panels, inner plastic bumper supports, John Deeres' lawn mower deck (programs I worked on during the tail end)
I found 3 of my panel broken once I pulled them from 5yr storage last fall. Cars and car doors where not moved in 5 years. And cars had been in garage storage for 10yrs to keep them out of the sun. This is what prompted me to look into it. And that data cannot be discounted if someone is going to spend thousands on a paint job to last the next decade and beyond.
Another point and plast to take a "peep", My black beater has not "popped yet", but when I measured w/the feeler gages, I noticed 20yrs of road dirt rubbed off the inside of the lip directly across from the metal protrusions. So I see where the metal was touching the plastic recently. My skin does not slide back and forth. So I know it does not rattle as I drive or close the door.
Okay, sorry for the soap box, that's why I put in power point, to get it to the point. Please be as critical as you need to be on this. I want to add every logical cause and educate all to stock up if you're in for the long haul.
I'll bring this up again during the next week long winter "freeze" this winter and have you all take a look at the gap. I'll bet more of you will see cracks mid winter to spring.
Thnx for all your help on this guys (and gals)
d
As a side note: (But that doesn't seem to be in question right now). Fundatmentally, the CTE's are not exact. I pulled the books and picked middle road CTEs for materials. I took a piece of broken fender about 4inches long. Put in it ice water, measured it. Then boiled it, measured it. I got a CTE of .00005, where the book gave ave ABS of .000056. Not bad.
Aggree that road vibration and door slamming will accelerate this. Will note to the pitch
Aggree UV degredation accelerates this. I believe this is noted in the pitch
Aggree modulous of elasticity decreases greatly as temperature drops. Fundamental characteristic in plastics and will add to pitch. Actually, I'll try and find a chart over temp on the strength degredation over temp.
Plastic does absorb moisture. But is not considered in design because test samples are equalized at 50% RH @ 75f for at least 48 hours after they come out the the 180F mold before testing. So the tech data sheets already have moisture content accounted for in the test data for the engineers to design to. Not planning on adding this one. But I like how you think!!
However, to have a .070" interference is a design flaw. Some fundamentals are proper material selection, tolerance stack up analysis (ProE and AutoCAD and do these very well) and function over environmental condtions (in this case temp), chemical exposure.
Maybe you're right and Honda punted and balanced the justified the risk as not life threating. Take a paper clip. Bend it back and forth 5x and it breaks quickly b/c bending in both directions. Take a spring bending in force under one direction and you get thousands of cycles before failure. The skin acts like a one dimentional spring due to the interference and eventually gets stretched in one direct every diaurnal day there's interfence. That may not have been a big deal to Honda, but I find it hard to chew when so many other features of the car are so well designed for long term reliability. The plastics industry really blossomed in the 1980's. I didn't joint until 1991 with the Saturn door panel program. They really pushed the limits w/ car panels, inner plastic bumper supports, John Deeres' lawn mower deck (programs I worked on during the tail end)
I found 3 of my panel broken once I pulled them from 5yr storage last fall. Cars and car doors where not moved in 5 years. And cars had been in garage storage for 10yrs to keep them out of the sun. This is what prompted me to look into it. And that data cannot be discounted if someone is going to spend thousands on a paint job to last the next decade and beyond.
Another point and plast to take a "peep", My black beater has not "popped yet", but when I measured w/the feeler gages, I noticed 20yrs of road dirt rubbed off the inside of the lip directly across from the metal protrusions. So I see where the metal was touching the plastic recently. My skin does not slide back and forth. So I know it does not rattle as I drive or close the door.
Okay, sorry for the soap box, that's why I put in power point, to get it to the point. Please be as critical as you need to be on this. I want to add every logical cause and educate all to stock up if you're in for the long haul.
I'll bring this up again during the next week long winter "freeze" this winter and have you all take a look at the gap. I'll bet more of you will see cracks mid winter to spring.
Thnx for all your help on this guys (and gals)
d
Keepin' it OEM