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#114017 06/02/22 09:24 PM
Joined: Jan 2016
Posts: 7,466
Likes: 143
NormK Offline OP
SENIOR TECHNICIAN
I need to replace the top starter motor bush on a 16hp Vanguard V twin motor. I don't have a bronze bush I could turn up so I was thinking of using Delrin. Anybody have any thoughts on how the Delrin would stand up?

Joined: Sep 2015
Posts: 2,052
Likes: 146
SENIOR TECHNICIAN & HISTORIAN
G'day Norm

I'd say it's not worth using Delrin ,Delrin will work but the question is for how long

Bad points using Delrin.

1 I've heard you machine Delrin at 800 rpm maximum otherwise it can burn with an invisible flame,
starters rotate faster than 800 rpm.

2 Delrin isn't as hard as alloy so won't last that long anyway..Alloy would work better as a bush.

3 Delrin deforms under load ,not great on a spinning shaft with load applied.

If I didn't have bronze for a bush I would use brass.

Norm I have brass here if you want some ,no charge.

Cheers
Max.

Joined: Jul 2018
Posts: 2,086
Likes: 80
SENIOR TECHNICIAN
Hi Norm

It theory the delrin should substitute fine.

It all comes down to repairability to me - if it is a 15 minute job to remove the starter again (usually is on briggs v twin but never know if chassis design inhibits this) then go the delrin.

If it is a pain to get at and you are preparing it to be sent 100's of km into a bush property where repair would be much harder/time consuming, then probably not worth trying delrin.

Dy the way, if the 13mm mounting bolts are being a pain, cut a groove in the bolt heads. Briggs recommended this years ago for 90s and 2000's v twin models, though a nut driver screwdriver would probably work better now. Don't know how old yours is.

Is it on that rideon with the seized brake?

Last edited by Tyler; 06/02/22 11:23 PM.
Joined: Jul 2018
Posts: 2,086
Likes: 80
SENIOR TECHNICIAN
Hi Max

I heard delrin can go a fair bit over 3000rpm when machining, though that could quite easily be with coolant. I do recall something about a methanol like fire

Sintered bronze whould probably be the best, but it would be a good experiment for delrin, provided it doesnt cause equipment downtime and repair difficulties

Joined: Jan 2015
Posts: 1,487
Likes: 23
AVB Offline
SENIOR TECHNICIAN
Max, Good Point on using Brass as a sub. And it can be gotten at plumbing suppliers. I just a 1/8" Schedule 80 section to repair a carburetor here. I had to use the sch 80 because of the outer and inner diamemsions I needed. Of course the brass will wear more than the bronze but it should still hold well.

Just a thought...

Joined: Jan 2016
Posts: 7,466
Likes: 143
NormK Offline OP
SENIOR TECHNICIAN
Thanks everyone for the replies
Max, thanks for the offer, I have to go to the bearing shop this morning to get bearings for a Ariens self propelled so I should be able to get a bush of some sort I can turn to fit
Tyler, it is the 20 year old Massey Ferguson that has sat here for years. I got a new Chinese carby for it but totally useless just ran way too rich and the governor was hunting so I got a $20 PZ30 motorbike carb and fitted that, and it runs very well, nice and smooth
AVB, that is always an option

Joined: Sep 2015
Posts: 2,052
Likes: 146
SENIOR TECHNICIAN & HISTORIAN
G'day Norm ,Tyler and AvB

It's interesting when you read other forums on machining, some people there have never heard of Brass bushes
for machinery etc and say you must use Bronze.

In certain applications brass bushes are the preferred bush of choice.

JCB for instance it's very common to use Brass bushes in the front end ,we know Bronze is harder longer lasting
normally but harder can mean more brittle and using a bronze bush in a JCB front main pivot could easily kill
someone ,driving down the road the brittle bronze bush breaks then if you loose control of the steering 7 tonne could go straight
through an oncoming car.

Hardness is a measure of a material’s response to local surface stresses and how it reacts to scratching, denting, etc. The Brinell hardness scale is one of the numerous hardness scales available and uses its own hardness indenter machine to grade a material’s response to a standardized force. For reference, typical glass scores 1500 on the Brinell hardness scale and lead scores 5; using these as benchmarks, Table 1 below clearly shows that bronze is on average harder than brass. A harder material is usually more brittle, and bronze follows this rule by being much more prone to fracture than brass. If workability is a necessity, brass is by far the better choice than bronze. However, if strength and resistance to wear are of concern, bronze may be the better option.

Brass is used instead of Bronze in some diesel piston pin bushes .

Old cars can have steel ,bronze or brass king pin bushes.

Another common use of Brass bushes is in old clocks and watches ,the idea here is if you used bronze the spindles
will wear out ,brass is used so only the brass needs replacing making repairs cheaper and easier.

More uses of brass bushes here if interested https://www.ehow.com/list_6811884_uses-brass-bushings_.html

Cheers
Max.

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Joined: Jan 2016
Posts: 7,466
Likes: 143
NormK Offline OP
SENIOR TECHNICIAN
Got a bush this morning, turned it up to fit and starter motor is back as good as new


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