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Post by Hoggwood on Apr 28, 2020 23:58:10 GMT -5
Hi Folks, Long time Terry Industries Homelite nut. I don't post as often as I would like, but I thought I would share. If this is not in the ideal place, perhaps it can be moved accordingly. I don't often run into problems with the ubiquitous check valve (assembly) used extensively on the HDC, HDB and SDC Walbro carbs. I've perhaps replaced/repaired 2 or so out of the dozens and dozens of carbs I've gone through. But, as parts supplies eventually dwindle for discontinued carbs, I figured I'd pitch my work around. No intent to step around any folks that are selling the OEM kits. Nothing beats OEM in a carb. The original check valve is made of nitrile (nylon insert) and approx 0.009" thick and approx 0.205" in diameter. I used an old rubber stopper hole punch from work that had an OD of 0.210". I used a round file to taper the ID until I had bore of 0.202". I punched several checks and the results were good. A few had stray nylon that needed to be carefully trimmed. As for the brass seat assembly, I know it is common to just pull them entirely. From experience, I know that in the pocket, there are 4 raised bosses that cradle the check. Above that there is room for the valve to move and check against the rim of the brass assembly. Enough room to get the old check out and a new one in without much difficulty. One can maintain the integrity of the assembly (heck even reuse the circlip and screen) and avoid having to thread and pull the check or use a mini slide hammer. In all, to remove the clip/screen/check and retrofit/replace screen/clip it takes about 10 min. If your glasses are strong enough and your hands are steady, you can shave a couple min. off. I used a HDC circa 1973 off of a Terry XL Auto. The original check, which was still supple and functioning well, was removed and replaced with the retrofit. Both OEM and retrofit passed well and checked hard when tested. Here is a comparison between the OEM assembly and the samples I punched. New OEM 86-523 Assembly on top. There is some shadowing but, they are uniformly round and when laid over the original match "perfectly". They punched out nice and round with the odd one holding on to some thread. A bit of trimming to clean them up.  New OEM top and a random sample below. They match up well in all dimensions.  |
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Post by Hoggwood on Apr 29, 2020 0:00:22 GMT -5
Clearance in the pocket for the valve to sit  Removed clip/screen/check (bottom left) Sample retrofit (bottom right)  |
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Post by Hoggwood on Apr 29, 2020 0:02:40 GMT -5
I laid the valve centered across the assembly and an appropriate blunt punch to (gently) seat it as far as possible.  Not quite in...but that is okay.  |
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Post by Hoggwood on Apr 29, 2020 0:06:26 GMT -5
I use a flat dental tool to work around the perimeter to flip the valve into the pocket. Like changing a bike tire.  A piece of copper wire to make certain it is smoothed out and flat. A final check, when laying flat, it should easily slide laterally when pushed in all directions.  |
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Post by Hoggwood on Apr 29, 2020 0:09:59 GMT -5
Laying flat, and a shot of WD-40 and fuel line to (wet) test the function. Passes and checks well.  7/32" with a slight chamfer works like a charm when setting the old circlip.  |
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Post by fossil on Apr 29, 2020 8:23:27 GMT -5
Good stuff Cory!
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Post by xl130 on Apr 29, 2020 12:40:19 GMT -5
Pretty cool! Great creative thinking and a very useful hack. Those darn check valves are a pain to pull and like you said Walboro has discontinued production for some of them.
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Post by dpress on Apr 29, 2020 14:54:44 GMT -5
Thanks for this very useful post, as these check valves seem unobtainable in the UK. Can you advise what material you used to make the new valves - I was considering using some left over pump diaphragm material from partially used carb rebuild kits? Any thoughts?
Thanks, Steve
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Post by Hoggwood on May 2, 2020 11:18:29 GMT -5
Thanks for this very useful post, as these check valves seem unobtainable in the UK. Can you advise what material you used to make the new valves - I was considering using some left over pump diaphragm material from partially used carb rebuild kits? Any thoughts? Thanks, Steve Hi Steve. I didn't measure the thickness of any newer pump diaphragms, but I do have a slew of old (gently) used OEM ones. They measured out essentially the same as the OEM check. I used the old diaphragms and punched out from areas that were entirely captive between the gasket and carb body. Essentially, "unused". I could get several from each one. I put together an early Super Mini this week from a box of nuts and bolts. I put the carb from above in it. I will fire it up and see how it idles and transitions today. The earlier HDC's had the additional acceleration circuit that fed through an index port in the throttle shaft. So, we'll see how that responds when transitioning impulse/fuel from the idle circuit to the main (retrofit) check when throttling. I expect the check will be fine, as I have had good success on SDC's using this same approach. If you want a sample(s) of those checks PM me. |
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Post by dpress on May 2, 2020 13:54:50 GMT -5
Many thanks for the additional information. I have lots of 'new' part gasket sets, and a hole punch of different sizes for leather, so will have an experiment soon, now that I know the correct size for the check valve, and can follow your excellent pictorial guide. Funnily enough the check valve I was concerned about is the one in my own early VI Super Mini.... This forum continues to be a mine of useful information from helpful folk. Cheers, Steve  |
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Post by ettrick on May 8, 2020 21:13:59 GMT -5
I like your post, and good timing as i am working on my check valve now. I have a carb with the light brown gasket material on my carb check valve. I wonder if this is from a replacement kit or original? I also have two carbs with no disc in there. I do not think they can disintegrate so somebody must have been in there before me.
Dan
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Post by Hoggwood on May 8, 2020 22:40:08 GMT -5
I like your post, and good timing as i am working on my check valve now. I have a carb with the light brown gasket material on my carb check valve. I wonder if this is from a replacement kit or original? I also have two carbs with no disc in there. I do not think they can disintegrate so somebody must have been in there before me. Dan Hi Dan, I can't really comment on the Teflon (tan coloured) material being used in carbs as check valves. I have never seen it used in carbs that utilize check valves. Namely, HDC/SDC and HDB. Generally, I am in carbs that are 30-40 years old. I know some manufacturers are supplying NBR (black), Teflon (brown) and Acetate (blue/clear) pump diaphragms in their carbs and kits. They do have different tolerances to ethanol and abilities to pump fuel. For me, some older saws "like" the original capabilities of the NBR diaphragms. I have had some instances where the teflon pumps did not cooperate with the saw fuel system. I don't think it would be possible to retrofit a disk of that Teflon material in the Walbro 86-523 assembly without pulling it. I am reasoning it would be too stiff and need to be folded somewhat to work it in there. It has much more "memory" when folding than NBR. Performance wise, I think it would function very well. It is much more resistant to ethanol, acetone, toluene and the like present in carb cleaners etc. The presence of ethanol in fuel and a few rounds of those strong solvents when cleaning carbs over the years accelerates the deterioration of those old check valves significantly. What carburetor(s) are you working on that have these Teflon checks? |
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Post by ettrick on May 9, 2020 8:27:05 GMT -5
I am repairing an HDB carb without a check in there by putting one from an HDC. When removing the one from the HDC that is when i found the teflon or brown check. It was a carb from a 360 saw. I bought some hollow punch tools to cut my own checks. It seems like the 7/32 size comes out the same as the check valve i had.
Dan
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Post by Hoggwood on May 9, 2020 9:28:20 GMT -5
I am repairing an HDB carb without a check in there by putting one from an HDC. When removing the one from the HDC that is when i found the teflon or brown check. It was a carb from a 360 saw. I bought some hollow punch tools to cut my own checks. It seems like the 7/32 size comes out the same as the check valve i had. Dan 7/32 is what I figured it measured out to be as well. Are you going to retrofit with the Teflon or NBR? Curious how difficult the Teflon may or may not be to install as well as the performance. |
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Post by ettrick on May 9, 2020 9:39:05 GMT -5
I have been practicing removing the brass part so i can put the stiffer material in if it is better holding up to fuel. What is your opinion on this? I am not doing very well removing the brass piece without some damage, i will have to find some better tools. I have watched the video on this but there not very good optics to see what is being done.
Dan
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Post by Hoggwood on May 9, 2020 9:56:32 GMT -5
What method/tool are you using to pull the assembly? I thought about taking a small driver and using a Dremel to rabbit a groove around the circumference and then using it like a poor man's slide hammer. On the thrift. I've threaded and pulled them before, but you ultimately have introduced some damage. The Teflon is significantly more resilient. The functioning dynamics are worth testing in my opinion.
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Post by ettrick on May 9, 2020 19:37:25 GMT -5
I have been using picks and small screw drivers that are bent some so i can reach through the hole and apply force underneath without touching the thin area. I have seen other thread using a slide hammer type tool, but unless it has a deep cut in it i would think it would still do damage to the brass.
Dan
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Post by xl130 on May 27, 2020 20:39:06 GMT -5
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Post by 5terrysupersaws on Jan 23, 2021 17:45:40 GMT -5
This a great thread, many thanks to Hoggwood for posting !!
Request this thread be moved to the " Fuel System " Board and a Sticky to the top be applied,
so it can easily be found and more information added . Thanks !
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Post by tangobravo on Feb 11, 2021 9:43:26 GMT -5
I understand these check valves are not a regularly serviced part and seem to be very reliable. Is there a recommended test you have to determine if it is functional/ not in need of service? Does the pressure test show if this is working? Not really clear to me how to best identify a failing one.
EDIT_-Think I just found my answer--Where else-- On Leons video list. Requires removing the welch plug again though!
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