ameyam

I know many people use Loctite on the engine head screws to hold them in place and prevent them from coming loose after the engine gets hot.

In my case, the threads on the carb retaining screws hole has slipped and I got it retapped. Now, the hole is slightly oval and the screw may not fit in perfectly snug, so the machine shop suggested to use loctite to hold the screw in place. What should I use (or which color)?

Ameyam

radius1x1

Blue

ameyam

Is blue permanent or red? I know one of them is removed by applying heat. If this carb doesn't work / stay in place, I plan to get a replacement carb. So I want the installation to be removable

Ameyam

AB Bob

My Feedback: (20)

Ameyam,
Blue is removable
Red is permanent (requires heat)

ameyam

Oh, then I stand corrected. I always thought blue could be removed with heat whereas red was permanent and would spoil the threads if I tried to remove it.

So I should go for blue then?

Ameyam

im_a_rcav8r

Another vote for BLUE. Another "trick" in addition to the BLUE thread lock is to put a drop over the head of the screw but only on 1/2 of the screw. This way you can see if the screw is turning as the blue color on the screw will be misaligned as the screw begins to turn.

As a last resort, if all else fails, you can fill the hole with JB weld let it cure and drill and tap a new hole. JB weld is fuel and heat resistant and very strong when cured.

Good luck

BarracudaHockey

My Feedback: (11)

Green is what I would suggest in that circumstance.

ameyam

Well, I got hold of the blue threadlock. What I really need to know is, will this thing I am doing work? I am pretty sure I can get the screw to hold with the locktite and I have the rubber o-ring intact on the carb. In short, there is no other likely source of air leakage that will cause the engine to run erratically.

I am ordering a replacement piston liner for this engine, so I will install the carb back after I install that. I want to also getting a replacement carb but that is out of stock at TH. Weird thing is, since I had added the carb to my shopping cart sometime back, it still shows the carb as in-stock in my cart. It will stay that way till I delete it from the cart and try to add it again. Dont know whether TH has "kept one aside" for me. So, if there is a fair chance that the engine will work properly after I install the repaired existing carb, I wont order a new one now

Please suggest

Ameyam

SeamusG

Per the Loctite website ...

Loctite® Threadlocker Blue 242® is designed for the locking and sealing of threaded fasteners which require normal disassembly with standard hand tools

Loctite® Threadlocker Red 271™ is designed for the permanent locking and sealing of threaded fasteners. ... It is only removable once cured by heating up parts to 500°F (260°C).

BTW - if you heat the aluminum crankcase above 270 F - you'll likely distort it PERMANENTLY resulting in things like the bearings not seating.

ameyam

Ok, but now I have the carb retapped and I am going to refit it back into the engine with the blue locktite and the original screws. Will the engine run same as before? Thats the only question left in my mind now. If it runs ok and I get a replacement carb anyway, its a waste of $80. On the otherhand, if it doesnt and I dont get a replacement carb, then I am stuck again

Pics are attached. The hole on the throttle level side is the one that is retapped


Ameyam

Airplanes400

My Feedback: (349)

Since the holes are re-tapped to a larger size, use a larger size screw. For example, if you re-tapped the hole from a 4-40 to a 6-32, then use a 6/32 screw. Problem solved!

JBweld does not do a good job if you re-thread. You can easily tighten the screw too much and strip out the JBweld. A heli-coil does a much better job. But in the first case, re-tapping to a larger size hole and screw is a very good fix.

SeamusG

Or better - step up from standard (6-32) to the next larger metric (3mm). That will allow for a smaller increment in hole size.

Gray Beard

My Feedback: (-1)

The machinist that did the work should have been able to tell him this. If the hole isn't round and you use a round screw you will have an air leak. The blue locktite will hold the screw so it doesn't back out again, it isn't a good filler, it will help a little but that isn't what it was designed to do. Just depends on how much the hole is out of round. I was thinking some high temp sealer but that can be put over the screw or used on the threads. After a complete cleaning to remove any and all oil heated JB weld could work. Hard to tell without the carb and engine in hand.

freakingfast

My Feedback: (3)

Blue or red Loctite works best if you clean out the hole and fastener first with acetone so that it's free of oils. Use caution (safety glasses) when blowing the acetone out of the hole(s). In the eyes that stuff hurts like a ........ ........

SeamusG

Geez Gene, machinist? Ialways just put the bit for the right tap into the drill and made a hole - then a little oil on the tap - and it's all good. I guess I'm not spending enough money on the hobby.

speedracerntrixie

My Feedback: (29)

Back in the day when I raced Q-500 with the OS 40 FSR abc engine we would occasionally have the same issue. As a field repair I simply put a 4-40 screw all the way through the carb and out the other side with a lock nut. There were nylon washers under the screw head and nut to seal. The temp fix worked so well I never changed it. There was no power loss that I could tell.

SeamusG

Speed - I was wondering how (un)important the amount of threads that extended into the air passage.

lopflyers

My Feedback: (12)

And how exactly do you know it hurts?

ameyam

Hold on, I didnt tap for a larger hole, only the first few theads seem to have been damaged, they were able to use the same 6-32 tap and the stock screw threads in ok. In fact, eveb before tapping, the scre wouldnt come out on its own, it just wouldnt stop turning. Somehow, a larger screw isint required yet. I havent tried installing on the engine to check but I dont think there will be too much of a problem once I use the loctite. By the way, I intend to use RTV sealant (silicone) over the hole to prevent the air leak that you are mentioning. I really wanted to understand how critical this task is and I think you answered my question

Ameyam

speedracerntrixie

My Feedback: (29)

Actually with what I know now I wouold clean the parts well with acetone and then install using JB Weld as a threadlocker. There really arent too many times when removing a carb is needed. Even if you do have to remove the screws later all that would be required is to heat up the screws with a 45 watt soldering iron and they will pop loose. I don't recall the OP stating what engine this is but I'm pretty sure that 6-32 would be the wrong size. 99% of what is manufactured for the past 10 years is going to be metric. 6-32 is close to 3.5mm and most of what I see with this type of carb attachment is 4mm. If one is trying to put a 6-32 into a 4mm hole then yes it's just going to spin. Verify the size screw needed, it may be a non issue with the correct size screw.

jaka

Hi!
The ASP .40 or Kyosho .40 GX (same engine) all use 3mm screws to hold their carbs. I have on several occations retapped the hole to 3,5mm and used blue tread lock to hold the screws.
Tread lock is not necessary to use on the head bolts! If those get loose it's asign of running too lean (to much heat).

ameyam

Ok, I stand corrected. Thats M3.5X6mm (looked up the manual). In that case, should I redrill for 4mm? I will also need to enlarge the hole in the casting for 4mm, right now the 4mm screw doesnt go through

Ameyam

Gray Beard

My Feedback: (-1)

Jim, go back and read Amey's first post/question. He didn't drill and tap the hole himself. He and I have been talking about it in the last week or so too so I knew what he was trying to do.
How important is the screw length? One friend here lost both carb screws, I just happen to have a pack of OS carb screws in my flight box but he declined my offer. He found the correct size of screws on the LHS wall but had to cut them down in length. His 55AX would run but it ran for crap. The screws protuded a bit into the carb barrel. I talked him into using the original OS screws I had, they were flush inside the carb and all his problems were cured so I would think the screws will create a problem if they protrude into th carb at all, they sure did on the 55AX.
Although I like to do everything myself, I have been known to use Clearence Lee to do some repairs for me. I know my own limitations!! Some things are just better leftto the prows!!

Gray Beard

My Feedback: (-1)

Sort of like my typing!!!

tony0707

CA glue on the treads will seal the threads and prevent an air leak around the threads that wb a bad thing especially for a glo engine-C A is gas and glo fuel proof epoxy is gas proof
I have simply JB welded a few of my carbs in to the crankcase with great results-carbs stay good for yearsheat with a butane torch to remove the carbseldom required