How to keep the carb from vibrating loose?

[Kez]

The carb is retained by a cinch bolt (draw bolt? not sure about the name). It keeps vibrating loose. If I tighten it more, the bolt just dig into the neck of the carb.

I can not JB weld it because I need to remove the carb to remove the back plate. Any suggestions?

kez

 

[robertpickard]

I bet it is a OPS carb lock tight it in

 

[jeff baham]

kez, if it is an ops carb you can drill and tap a set screw under the houseing and use some medium strenght lock tight on the carb neck and set screw.

 

[Kez]

Thanks guys. If I apply Loctite to the neck, will I still be able to remove it? Do I need to apply heat? I have green Loctite.

Adding a set screw is my last resort. As much as possible I like to keep my engine stock.

Thanks for the replies

 

[TUNLBOTR]

Kez,

If it has the 2 piece draw bar, where the bolt passes through one side of it and threads into the other, take the side that passes thru, and grind just a little off the end where the draw bar scallop is, that will shorten the bar and let it draw a little tighter.

 

[moparbarn]

blue loctite seems to hold up better to the vibrations from nitro motors. the red & green dry harder, & will crack/shatter with the vibrations that our motors produce. the blue remains somewhat more pliable, & resists cracking better, imho. also seals better. heat is recommended to remove any of the different loctites, not much, a bic lighter will work on small stuff.

 

[Don Riek]

Kez,

I respect your wanting to keep the carb stock, however if that proves frustrating you can replace the drawbolt with stainless machine screw, 6/32 or 8/32 may fit, depends on your application. The fit needs to be slightly larger than the hole left by the drawbolt. The idea here is to SLOWLY thread the machine screw into the case, cutting threads as you go. The correct size screw will cut slightly into the carb body, securing it until you remove the screw. You can apply loctite to the screw to keep it from backing out, but this would be rare.

I did this at a race a few years back when I had tried everything to keep the carb attached to my Rossi outboard powerhead, including JB Weld and Plastic Weld. I never had the carb back out again. If you don't like the hex head showing, you could probably find a long set screw to use instead.

 

[ZIonOB75]

blue loctite works for me too..

 

[happybradboating]

Kez,

On all my old style Picco 67 and up I drilled to hole in the backing and through the carb. I use 440 bolts which are rather small. Then cut them to length so when you look down the carb you don't see the bolts sticking out. In addition, no one will see the changes when the boat is on the lake, work on the boats paint job instead.

 

[Kez]

Thanks all for stopping by and offering your solutions. Lots of great ideas to follow up on. From all the replies, it appears to be a common problem. I do not understand why manufacturers are still using the draw bolt to secure the carb. I have better luck with set screws; and in the case of a drum intake, the carb is bolted to the back plate and I have never had one come loose.

Tunlbotr, it is a one piece draw bolt. The two piece design tends to work a little better (K& B) but can still come loose.

moparbarn, I have both green and blue loctite. I think I may try to put some loctite when I assemble it. I believe I will need to heat it to remove the carb. Not sure if the carb O-ring will take the heat though.

Don, Interesting idea. I may give it a try it the Loctite approach did not work. If I am going to try it I may use a tap to cut the thread first instead of a SS bolt. So you have tried JB weld and the carb still come off? I would have thought the JB weld would be a permanent fix.

Happy, I will check and see if there is enough material in the back plate to tap for 4-40. As for wanting to keep the engine stock, it is kind of a personal thing ;-) I enjoy building and running RC boat as much as I enjoy collecting the engines. I would run an engine until it is over the hill or can not find anymore spare part. Then I would put them away in my collection. I guess I can live with tapping a 4-40 hole if this will keep the carb from falling out.

kez

 

[moparbarn]

kez, what is the length & od of the draw bolt? also the length & depth of the cut out where it fits around the carb? i have a handful of 2 piece drawbolts that i got in a box lot of parts. don't fit my .21's. you're welcome to a couple if they will fit your motor, all i'll need is an addy.

 

[glenng]

Blue Loctite- Red-you must heat up with a torch to remove and green is FOREVER:lol:!

Glenn

 

[Mike Larson]

Guys... he has the old school silver picco's that threw the carbs normally... Basically they came with a little teeny set screw first.... ( drilled out and retapped 4-40) Kez, the loctite solution is where it's at..... and a retap/larger screw....

I got away with normal epoxy in a pinch, too... ie: they come off at a race!....

Cleaned, and a good goop will actually form a good seal at the junction because they like to leak there also.....

IMO, the vibration and the static pressure from the servo linkage forces them off.... adjust your endpoints only to get enough to open and close... AND glue it on there...... test well Mike

 

[Mark Bullard]

What kind of carb is it? Does it have a positive stop on the barrel?

 

[Kez]

Moparbarn, I will measure the draw bolt and PM you the dimension. Thanks for offering to help. My feeling is that the bolt has an OD too small for a split design.

Mike, actually it is not the Picco P-45 that's giving me grives. It's an OS 46 that I bought some 25 years ago this past weekend and it shock itself apart. In fact, other engines in my collection, inclusing yes, an OPS, that use the draw bolt all have similar problems. My K&B 7.5 O/B has a split draw bolt and that worked better.

Mark, the Picco has the early black carb with no positive bolt on the barrel. The carb is bolted to the housing with 2 3mm screws. Very bulky design.

Thanks,

kez

 

[Mark Bullard]

Moparbarn, I will measure the draw bolt and PM you the dimension. Thanks for offering to help. My feeling is that the bolt has an OD too small for a split design.

Mike, actually it is not the Picco P-45 that's giving me grives. It's an OS 46 that I bought some 25 years ago this past weekend and it shock itself apart. In fact, other engines in my collection, inclusing yes, an OPS, that use the draw bolt all have similar problems. My K&B 7.5 O/B has a split draw bolt and that worked better.

Mark, the Picco has the early black carb with no positive bolt on the barrel. The carb is bolted to the housing with 2 3mm screws. Very bulky design.

Thanks,

kez

A split draw bar type should fix the problem