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When I rebuilt the 330 in my '67 CS convertible about 12 years ago, I opted to leave the ports and combustion chambers stock. After the water pump failed and someone overheated it and stuck a valve while I was overseas, I find myself going back through a relatively low-miles engine. (Less than 20,000, anyway.)
This time around, I decided to do some cleanup and minor reshaping of the ports and chambers, and fill the exhaust crossovers. After much reading here, on ROP, and on Performance Years Pontiac forums, I decided on a 2,800* ceramic adhesive - Resbond 940HT.
Several PY members report things like "5 race seasons with no issues," or "tore down at 12,000 miles and found no erosion" with the Resbond, and it's much easier to work with than molten aluminum. With that in mind, I contacted Coltronics in NY and bought a quart of Resbond for $99. (One pint is more than enough for one set of heads, but I have the 403 coming out of my '79 T/A next, so I wanted enough to do both.)
After disassembly, cleanup, and magnafluxing, I did some grinding on the heads until I was reasonably satisfied with the condition of the ports and chambers. Resbond is supposed to be so easy to work with that masking tape will seal the intake side and allow a pour into the exhaust ports, but I decided to play it a little safer and I used small rectangles of rubber held on by scrap wood that I drilled for the intake bolts: 01pluggingholes_zps86cc2255.jpg
With both intake side ports blocked off, I positioned the heads so I could pour into both without moving either: 02headsready_zpsf532a404.jpg
I tried to angle the heads so that the area I needed filled would be level -
here's a closeup of the angle down into the exhaust port: 03closeup_zps8cebe74c.jpg
Here are my supplies... I ended up not using the funnel, and I added a second 1-pint container so I could measure the fluid in one and the powder in the other: 05supplies_zps62950947.jpg
I used a spoon to move the powder from the Resbond container to the pint container, mostly to avoid a poof of airborne powder - the stuff is supposed to be an irritant, and I didn't feel like being irritated. 07measuring_zps3d53ed33.jpg
The correct mix as shown on the container is 100 parts powder to 30 parts liquid. I did this by weight, using my refrigerant scale (accurate to 0.1 oz, which is close enough for this). 08precision_zps0369d0d0.jpg
Next, I poured the liquid into a quart container and gradually stirred in the powder: 09mixing_zps256de2a8.jpg
This shot shows the consistency of the mix, which mostly reminded me of plaster or drywall mud. One of the users on PY posted that he mixed his to the consistency of pancake batter to aid in pouring. I think when I do the next set of heads, I'll use a little more liquid; this dry mixture was probably slightly more difficult to work with than a wetter mixture. 10consistency_zps905af892.jpg
Here's the first scoop going in. The mix was right on the verge of being pourable, but I decided to scoop it. 11firstscoop_zps117a6c01.jpg
I was a bit messier than I had hoped to be - we'll have to see if that will clean up with a wire wheel or the carbide bit I used on the ports. After I was happy with the level of the Resbond, I used my mixing pushrod to poke at the mixture to hopefully get rid of any entrapped air. (Another reason to go with a wetter mixture next time.) 12messy_zps2d9f7e9f.jpg
Next I used a steel scribe to scrape any extra Resbond off the valve seats, just in case it doesn't want to come off with any of my tools. The heads are going back for a valve job as soon as this sets up, but no sense taking chances. 13cleaningvalveseats_zpsadfbff3d.jpg
Here's a look at the ports after I was finished with the pour and cleanup of any wet Resbond: 14finished_zps5f4931b5.jpg
At two hours drying time, it feels like unsanded drywall mud. I'm curious to see if the surface is workable, or if that's the finish I get. Either way, it should be an improvement over unfilled crossover ports. 17twohourslater_zpsb0e6ce5a.jpg
By the way, the cure time is 15 minutes at 200*, or 24 hours at room temp.
After it cooled, I beat on it with a hammer. I was able to get it off the pushrod, but it didn't break apart. I'm reasonably confident that its trapped into the complex port shape enough to keep it there, but time will tell.
After looking at those, I'm again wishing I'd gone with a slightly wetter mixture, although I'm sure the appearance is the only thing that would have been improved - the functionality is the same.
I have done the finish cleanup with the flex-shaft dremel and the carbide bit - the Resbond can be shaped with about the same effort as cast iron. I'll get some pictures and post them soon.
Next step is off to the machine shop for a valve job and resurfacing. I hope to have the bottom end back together before I get the heads back, so it may go back in the car soon.
As promised, here are a few pics of the "finished" product. While it doesn't look nearly as good as the other ported areas, I think it's a vast improvement over the big open hole that the original design design had.
The heads are back from the machine shop and bolted to the engine. While I neglected to get any pictures, the shop reported no problems cleaning, machining, or assembling the heads, and I could not see any visible effect on any of the ceramic material.
Bumping an old thread... I got home from summer vacation in August and finally got the '67 running earlier this month. So far I don't notice much different from before I filled the heads; the intake is cooler to the touch, and the exhaust seems to have a bit more of a "blat-blat-blat" sound when I get on it, but that may be just my impression. I drove it for years and years with some no-name turbo mufflers that came in a $300 pre-bent kit exhaust from Year One... I switched to DynoMax SuperTurbos shortly before I took the engine out, and I may not be used to the different exhaust note. No chunks or rattles from the Resbond, though, so it seems to be holding up ok in the 50 or so miles I've driven it during ring seating.
On a side note, my starter took a crap while it was off the engine, and I ended up putting on a RobbMC Pontiac starter I still had new in the box from one of his promotions some time ago. Bolted right up and turns the engine over with authority.
I haven't heard any grief from the guy I sold a set of heads to 7 months ago. I told him what I used to fill it. I still have a lot of it left, and made a thinner solution to pour into the head like you suggested.
i recently received my resbond order. after talking to them on the blower, they say that the shelf life of this is 6 months after you open it. so, since i'm only doing 1 set of heads, it seems as though i'll be having enough left over for another set of heads. i won't be doing another set any time soon, so, the remainder will be for sale.
That is cool information. I've often wondered if there is an alternative to using molten aluminum. Not everyone has an acetalyne torch in their garage. Thanks for sharing.
last friday, i did my filling at the machine shop that is doing my motor. the machinist was intrigued with this product. i mixed it up 100 parts powder to 30 parts liquid and found it was a little thick, so i upped the liquid by about 6 grams on the 30 gram scale. it poured better then. i used flat aluminum flashing and duct tape to hold the mix in the crossover side. iirc, it took about 600 grams of powder to do both G heads. the heads were then left to sit on the bench and cure for the weekend. on monday morning, jim(machinist) took the leftover mix(maybe 20 grams) that i had left in the mixing bowl to test the properties once cured. he was not impressed. it abraded very easily and was quite brittle. it did stick like nobody's business-he had to pry it off the plastic container. needless to say, he had serious concerns about this product holding-up in actual use. i then called cotronics to ask wtf. the thing they leave out in all of their literature is, this product needs to be "fired" to achieve the final hardness. he said to put the head in an oven at 250*f for 2-3 hours. jim did this with 1 head, and when the cycle was over, he left it cool in the oven overnight. i called him the next day to find out what the results were. VIOLA! he was unable to even mar the surface with a knife, before "firing" he was able to scrape it with his fingernail. so, we're both very happy with the results, now. the other head will get "fired" next week.
the drawbacks to this product are that cotronics has a minimum order of $60 before shipping, if you don't meet this minimum, they charge you a $15 fee. i ordered the quart kit, i figured i could sell the remainder. they do sell a thinner for this product, but it doesn't meet the minimum and would've taken another roughly $75 to actually get into my hands. apparently, there is no problem with increasing the amount of liquid activator by a small amount to make the mix more pourable. the quart kit totaled $120, delivered. i still have over half remaining. the package states that the product should be used within 6 months of shipment.
I wonder if just running the motor is equivalent to Fireing the product 250f isn't really that hot
it may be a bit risky depending on how fast the firing hardens the resbond. that area of the head is a violent spot. and working with the unhardened resbond would likely be difficult, because it's so soft and powdery.
olds64-i'm happy to add to the knowledge base, especially when it's a positive experience.
Sorry to go off topic, but I've been trying to figure out if filling the crossover ports is beneficial for a street driven, daily driver.
I read somewhere (probably on the internet, so it must be true-lol) that the intake manifold needs to be warm to keep the fuel atomized in the incoming air/fuel mixture; a cool manifold will cause the fuel to condense out of the air and onto the the cooler surface of the intake runners. In principle, a cooler air temp means a more dense air/fuel mixture, but maybe blocking the crossovers is only a good idea for race motors, and not daily drivers. I look forward to your "schooling". Thanks!
In principle, a cooler air temp means a more dense air/fuel mixture, but maybe blocking the crossovers is only a good idea for race motors, and not daily drivers.
Your logic is completely sound. The aftermarket Edelbrock manifolds come with aluminum bungs to put into the cross over. I've seen many threads where folks use melted aluminum to do what Mike and Bill did with the Resbond 940HT.
FWIW, I have an Edelbrock intake on my 71 98 and I didn't install the aluminum bungs in the exhaust crossover. I might look into this Resbond 940 HT though. It seems like it would be easier to use than melting aluminum with an acetalyne torch.
too much risk of warping/cracking a head for my tastes, using the molten aluminum method. and then there's all the fooling around with heating the head, and keeping the molten aluminum hot enough to flow properly while pouring, etc.
the other gain (besides keeping the intake cooler) is that you get the 2 center exhaust ports isolated from each other. i'm using w & z manifolds which take advantage of the separation, headers would also utilize this benefit.
Just an update, since people are still following this thread. Mine's still running fine with no external evidence of an problems with the resbond. I don't know that I'm interested in pulling exhaust manifolds off to check the condition internally, so unless I experience some problem with the engine, I'm going to assume it's holding up just fine in there.
Thanks for the update Mike. I would say if you assembled everything and have been running the car on the road you aren't going to have any problems with the Resbond. When I get home I'll be on this stuff like a hobo on a baloney sandwich. Its a resonably priced investment that =
too much risk of warping/cracking a head for my tastes, using the molten aluminum method. and then there's all the fooling around with heating the head, and keeping the molten aluminum hot enough to flow properly while pouring, etc.
the other gain (besides keeping the intake cooler) is that you get the 2 center exhaust ports isolated from each other. i'm using w & z manifolds which take advantage of the separation, headers would also utilize this benefit.
Just an update, since people are still following this thread. Mine's still running fine with no external evidence of an problems with the resbond. I don't know that I'm interested in pulling exhaust manifolds off to check the condition internally, so unless I experience some problem with the engine, I'm going to assume it's holding up just fine in there.
Mike and others,
Any way to keep the Resbond from sticking in the valve seating areas?
I know you said the bowl area needs some grinding, I'm just wondering if I have to bring the heads back to the shop for machine work.
The Resbond is an afterthought, as my heads have already had a valve job, but are not installed on the engine yet.
George, this stuff mixes up to a consistency between pancake batter and cake batter. If you think you could use masking tape or contact paper or something else and keep the heads clean while pouring cake batter into the ports, you can probably do the same with the Resbond.
I knew my heads were on the way to the shop after I finished, so I wasn't as careful as I would have been if they were ready to go on the engine.
Hey I'll buy up any resbond someone has up for grabs here in the next week or so, if I can't find some quickly I'm gonna just forget it this time around
It's been some time, but I just filled a second set of heads with a new batch of Resbond 940HT.
It cost me $141 including ground shipping.
I used 18 oz of a 3 lb container. That leaves well over half remaining.
I'll sell for $70.
BTW the first set of heads filled have been in my '72 Cutlass for a few thousand miles.
No issues I can tell.
Thanks for the update, rootney. I'm starting to develop what I suspect is a lifter tick, so I may be pulling my intake soon. I'll try to remember to update this thread with my findings; I've been curious how it's holding up.
TTT - Curious if anyone has an update on this products long term stability.
Not yet, but at some point in the next couple of years I have the freshly built 400 from my dad's '67 442 going into my '67 Cutlass Supreme convertible.
I'd imagine I'll pop the 330 apart and see how things are holding up
Is there a reason to not just fill the intake instead of the heads, and welding a block plate to the olds intake gasket tin pan to keep the filler product from ever falling into the head.
Seems to me, If a piece of this restobond broke off, it make a mess of an engines valve seat,valve, piston top, cyl wall, chamber/etc.
I know when I used an intake without the crossover, I had carb icing issues on longer drives if the temp was 62 or less.
A race engine that is opened up every season this might be not as much of an issue, as you look it over and it is short runs and low miles/use. but in an engine that never be cracked open for 50k or more. I don't kno if I'd be willing to chance it. At least not in the heads.
Last edited by CutlassMarc; Jul 11, 2025 at 01:51 PM.
This is a bit over the top, but I machined the ports with a tapered end mill, (5 deg.) and made a plug to match, plug is larger than head port a bit so can't fall into head.
I do tool, die and mold building, semi-retired so have some extra time.. Tapered plug seals on the 4 sides and prevents it from moving into manifold, may leak a bit but should seal most of it. Opening before cutting Milling opening with tapered endmill Aligning manifold to mill Aluminum manifold plug
[QUOTE=BILL DEMMER;613042]update on my resbond 940ht experience:
last friday, i did my filling at the machine shop that is doing my motor. the machinist was intrigued with this product. i mixed it up 100 parts powder to 30 parts liquid and found it was a little thick, so i upped the liquid by about 6 grams on the 30 gram scale. it poured better then. i used flat aluminum flashing and duct tape to hold the mix in the crossover side. iirc, it took about 600 grams of powder to do both G heads. the heads were then left to sit on the bench and cure for the weekend. on monday morning, jim(machinist) took the leftover mix(maybe 20 grams) that i had left in the mixing bowl to test the properties once cured. he was not impressed. it abraded very easily and was quite brittle. it did stick like nobody's business-he had to pry it off the plastic container. needless to say, he had serious concerns about this product holding-up in actual use. i then called cotronics to ask wtf. the thing they leave out in all of their literature is, this product needs to be "fired" to achieve the final hardness. he said to put the head in an oven at 250*f for 2-3 hours. jim did this with 1 head, and when the cycle was over, he left it cool in the oven overnight. i called him the next day to find out what the results were. VIOLA! he was unable to even mar the surface with a knife, before "firing" he was able to scrape it with his fingernail. so, we're both very happy with the results, now. the other head will get "fired" next week.
the drawbacks to this product are that cotronics has a minimum order of $60 before shipping, if you don't meet this minimum, they charge you a $15 fee. i ordered the quart kit, i figured i could sell the remainder. they do sell a thinner for this product, but it doesn't meet the minimum and would've taken another roughly $75 to actually get into my hands. apparently, there is no problem with increasing the amount of liquid activator by a small amount to make the mix more pourable. the quar kit totaled $120, delivered. i still have over half remaining. the package states that the product should be used within 6 months of shipment.
This sounds like alot more work than melting zamak z-12 at 25. Bucks for 4lbs.
The zinc alloy only has a melting point of 700-810 degrees so I am assuming it can't get that hot in that area of the head if Joe Mondello has been doing it for yrs with no issues. Unless this was for drag racing not street use? Has anyone used zamak Z-12 alloy instead of a piston or 940ht?
. Tapered plug seals on the 4 sides and prevents it from moving into manifold, may leak a bit but should seal most of it.
