• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

Engineering Question - Epoxy Weld Aluminum to Steel

Share this page

D

Duropar1

Freshman Member
Country flag
Offline
Hi: I have to attach an aluminum collar 1” wide with an ID of either 2 3/4” or 2 11/16” to a steel pulley hub (Morgan TR3 engine) of 2.705”. The collar has two set screws.
1) Which JB Weld, Loctite or similar epoxy product will give the best bond between the aluminum and steel?
2) Are we better to get the larger ID collar and have a gap of 45 thousandths? Or the smaller ID and sand the inside of the collar to allow it to fit over the shaft with minimal gap? ie. What is the ideal gap between the aluminum and steel to be welded by the job weld? Thanks
 
If there’s room why not add an additional set screw to each hole. Tighten each set screw to the hub and then use the additional set screws to lock it in place.
 
Gliderman8 said:
If there’s room why not add an additional set screw to each hole. Tighten each set screw to the hub and then use the additional set screws to lock it in place.
Click to expand...
Not sure what you’re suggesting Gliderman? There is currently one set screw in the collar and I was planning on adding one more to balance the unit. There’s only one hole now and I can’t put in 4 set screws because I have to drill and tap four cap screws from the front face of the collar to hold the fan so 4 set screws would be too many. I’m more concerned about which epoxy to use and whether a 45 thousandths gap would be too large. Thanks
 
I think I got it now! You mean screw one set screw on top of the other to lock it in. I’m not sure if there will be room for two. We haven’t got the collar yet so I don’t know how much room there will be.
 
Duropar1 said:
I think I got it now! You mean screw one set screw on top of the other to lock it in. I’m not sure if there will be room for two. We haven’t got the collar yet so I don’t know how much room there will be.
Click to expand...
Exactly what I meant
 
3m panel adhesive would work also. JB weld is good, I have used it inside an engine and it is still working after 20 years.
 
I’m looking at JB Weld, but the problem is there are about 40 varieties. Any thoughts on which one is best to attach aluminum collar to steel pulley hub? And whether 0.045 gap is too large?
 
Duropar1 said:
Not sure what you’re suggesting Gliderman? There is currently one set screw in the collar and I was planning on adding one more to balance the unit. There’s only one hole now and I can’t put in 4 set screws because I have to drill and tap four cap screws from the front face of the collar to hold the fan so 4 set screws would be too many. I’m more concerned about which epoxy to use and whether a 45 thousandths gap would be too large. Thanks
Click to expand...

If it were me I'd go with the smallest possible gap, since even 45 thousandth could let the thing get off center while the epoxy is curing. I'd also rough-sand both surfaces to give the epoxy some coarseness to grip into. What is the function of this collar ?
 
Agree with YakkoWarner: epoxy is a mechanical bond (meaning it grabs on to crevices for adhesion), so make sure you have a rough surface for it to stick to. And while small clearances are good for centering, epoxy is best with a (somewhat) larger gap. (For example panel-bonding epoxy has microballoons to create the gap.) Tight clamping is generally not recommended for epoxy adhesion.

Consider the temperature the epoxy will be exposed to in selecting the right stuff. Low viscosity (runny) is better for small gaps, to get into little cracks, so I'd avoid any "putty" type compound. Looking at the JBWeld page, and selecting "high temperature", it seems the ordinary stuff is the way to go. > J-B Weld Twin Tube <

Good luck!
 
Have decided to try the 2 11/16” ID collar and go with Loctite 648. I contacted JB Weld and they advised a larger gap (0.060+”) would be advisable. Loctite advised a small gap works best with 648. I’ll rough up the outside of the steel hub and grind out the inside of the collar to fit over the hub and coat with Loctite 648. Only question left is whether to drill/tap one extra set screw or three more. I think one (giving a total of two) should be enough. Thanks all for your thoughts!
 
To answer YakkoWarner’s question, the application is for a Morgan Plus 4 fan. The Morgan used a white metal collar over the TR3 water pump pulley hub to mount the fan. Triumph apparently mounted their fan to the crank pulley so there is no sleeve on their water pump pulley hub. I was unable to source the Morgan pulley hub with sleeve so have to make my own.
 
I would only use metal bonding epoxy here, for a number of reasons. Not the least of these is the dissimilar
metals.
My plus 4 has the Miata 1600 so that is my solution to orphaned parts.
Mad dog
 
I was going to suggest the smaller collar with Loctite 609 (because that's the retaining compound I know). 648 is the same concept as 609 except that 648 has a higher temperature rating and slightly larger gap filling (0.13mm for 609, 0.15mm for 648) so I think you've made the right choice.
 
Back
Top