Mold lines in the sidewalls of rubber tires

[TonyH]

I'm working on the first release of the Gunze Sangyo Ferrari 250 GTO (G223:4000) with the white metal parts. 

I've noticed a lot of issues with the surface of the metal parts but I didn't think to examine the tires until I was well into building this kit. I've discovered what some have referred to as cold mold lines in the rubber tires. I'm not sure what the correct term is but I can say that it is a set back if you intend to use the kit tires. 

I think they're too deep to sand and smooth without significantly altering the profile. Has anyone encountered this with a rubber tire? If so, did you find a filler or other solution to repair the surface?

[espo]

I would try and contact the kits maker and see if they wouldn't replace these tires for the reasons you have mentioned. 

[StevenGuthmiller]

Can you flip the tires and use the other side?

 

 

 

Steve

[JollySipper]

or maybe repair the tire, then repaint it in a rubber black?

[Shark]

You might check with Harold Bradford at Historic Racing Miniatures, he probably makes something that would be a good or even better replacement.

[Mike C]

You have more than just mold lines in those tires. You have some flow lines too.

[Vintage AMT]

I would cast one and then repair it, then cast four good ones...

[Ace-Garageguy]

3 hours ago, Vintage AMT said:

I would cast one and then repair it, then cast four good ones...

Best answer...or just use different tires, assuming you have a stash of parts.

The kit tires from that particular Gunze kit are somewhat undersized anyway, IIRC.

Barring that, there are several flexible 2-part epoxy-based fillers (made for flexible parts repair) available from bodyshop suppliers that MIGHT work, possibly requiring an adhesion promoter, and refinish with a flexible black coating (SEM or Mar-Hyde, etc.) as Mr. Sipper suggests.

Not knowing exactly what material those tires are made from, I can't make specific recommendations.

 

Edited February 23, 2023 by Ace-Garageguy

[peteski]

Yes, those Gunze tires can be problematic.  I have seen this problem in the past. And I'm not sure what material they are made of, but it is not the standard rubber often used in Japanese kit tires.  It seems like some sort of vinyl/rubber hybrid, but not the same vinyl most American manufacturers use.

I have the Gunze Ferrari 250 SWB kit which I believe uses the same wheels and tires, and mine does not have those flaws.  If the flaws are visible on both sides I don't really have any good suggestions on how to repair them, other than replacing them with some other tires.

[TonyH]

Thank you for some great ideas folks! I'll try to respond to most based on my current time line and skill set. For background, my goal for this kit is to build it for competition in box stock classes. Otherwise, I wouldn't hesitate to locate a .stl file and fire up the trusty 3d printer. If someone knows of a file out there that replicates these tires, I'd be extremely interested!

I would try and contact the kits maker and see if they wouldn't replace these tires... -Espo The last issue of this kit was 1989. From what I can tell this issue has plagued this kit since it's initial release in 1985. I contacted some seller's on eBay that had open kits and they're reporting the same problem too. You'd think it would've been addressed after the first run. 

Can you flip the tires and use the other side? -Steve Unfortunately, they're on both sides. 

Repairing the existing tires. A few folks. Attempting to fix these was my initial thought. I've never tried to repair a rubber or vinyl tire like this. I will definitely be investigating some of the suggestions mentioned above. 

You might check with Harold Bradford at Historic Racing Miniatures. -Shark. That's interesting thought as well. I reached out to him last month in an attempt to locate some replacement clear parts for his Daytona Coupe that have yellowed in my kit. Unfortunately, I haven't heard anything in return.

I would cast one and then repair it, then cast four good ones... - Vintage AMT I do like that suggest as well. However, I've never attempted to cast anything beyond foil casting. I'd like to have the car done for a show next month, if not, definitely May. If anyone is around the Madison, WI area and would be interested in casting a few please reach out. 

Thanks again guys. I greatly appreciate all of the input and I definitely have some avenues to pursue. I'll be sure to follow up with whatever solution I come up with.

[peteski]

Well, if the model will be entered into box stock category, then just use those tires as they are. After all, they came with the kit, and getting replacements is practically impossible.  If you noticed, my tires have rather dull surface (as a rubber tire should have).  I assembled those wheels about 25 years ago (still haven't finished the kit), but if I recall correctly I rubbed them with a toothbrush and some household scouring powder.  It took some elbow grease, but I think they came out looking pretty good.  Maybe if you did something similar, the flaws would not be as apparent.

[NOBLNG]

You could maybe carefully fill the cracks with some black butyl caulk? It wouldn’t be perfect, but it would be less visible.

[TonyH]

Hey folks. I ended up trying the black automotive bumper repair stuff. It did a great job of adhering to the tire but it's quite thick which made it difficult to use in a small area.

It got a bit messy but I was ultimately able to get the sidewalls to look respectable. I sealed them with a matte acrylic clear and painted flat black. 

I'm not completely happy with way yhe tread and sidewall detail looks. So, I ordered some black, rubber-like resin for my 3d printer. Now I just need to figure out how to draw up a CAD file. 

I included a pic of how it looks right now. I'm still finishing up some final details and I've come up with a plan for the headlight lens I'll post later. 

 

Thanks again!

[peteski]

Nice save Tony!