Crank Dowel Pin - Desperate & Frustrated

[Grady Clay]

The good news it is repairable.

You will want a new pulley. Be sure to get another that is 134 mm diameter for the fan belt. I would also get a new bolt and washer. Check the bolt fit in the crankshaft.

Extracting the remains of the pin is a challenge. There are lots of options. Critical is to not damage the crankshaft - it is softer steel than the pin. The pin is a close ‘slip-fit’ in the crankshaft and an interference ‘press-fit’ in the pulley.

It is useful to fill the space between the seal and crank with heavy grease. You can put a greased thread around the bearing. This will collect any shavings. You will want to install a new seal when finished.

The condition of the pin hole in the crankshaft is critical. With a new pin and new pulley, there should be no rotational (angular) play between the crank and pulley.

If you find play, find TDC of the engine and then align the pulley to Z1. You can drill for a 2nd pin without causing damage. Drill the 2nd pin at about 90° from the original (not 180°). Start small and ream to the proper ‘slip-fit’.

Keep in mind the cost of the best tools and proper procedures pale in comparison to a crankshaft.

Best,
Grady

[1990C4S]

Originally Posted by Gunter

Machining a new set-up at 180 degrees cannot be done in situ and is way too involved and costly.

Make a drill jig and it won't be very difficult. Locate the jig using the OD of the shaft, and the existing dowel hole (visually). Add a pilot hole in the jig 180 degrees away. Bolt it on, drill, and ream. Done. I could do the entire thing in under two hours, including making the jig.

Or do it the way Grady suggested. Either will be fine.

You don't even have to ream it. Use a roll pin rather than a dowel.

[Nine9six]

Originally Posted by mholbrook38

Titanium drill bit. BE CAREFUL, Titanium will drill through almost anything.

My suggestion would be to source a preimium carbide drill bit for the job. Carbide will drill through almost anything. Titanium is a hard coating for high speed steel for improved wear resistance, but no where as hard as carbide or as suitable for drilling hardened steel. You do NOT need extremely high spindle speeds for a carbide drill to work. Normal drill speeds will suffice.
Take your time and start with a smaller carbide drill bit prior to using the largest drill size without drilling into the crankshaft, Center punching is critical, as this will dictate the final size drill you can safely use. If you are going to error, do so towards the pulley and not the crankshaft. Grady gives excellent advice on using heavy grease to catch metal chips.

As a point of reference for my recommendation; carbide will cut high speed steel. Ask any machinist who has broken a high speed steel drill bit off in a hole. EDM, or a carbide drill are your choices for removing a broken high speed steel drill bit.

[Dorsh]

Thanks guys for all the suggestions. I'm glad to hear its repairable! I bought this car 16 yrs ago when I was 19 and been through almost everything imaginable until this. Somehow this will work out it it's just going to take a little time.

1990C4S, I live in Orlando, FL.

After the pin sheared there was very small portion of the pin extruding from the camshaft but not enough to grasp with any type of pliers. Initially, I cut a slot in the pin with a dremel to see if I could apply some torque to loosen it but no luck.

I then took a dremel and created a coned surface into the pin to assist with drilling. I center punched but haven't been able to scratch the surface with a titanium drill bit. (Carbide next if necessary)

I do have the motor partially lowered with the muffler, mount, rear tin and lower rear valance removed to allow as much room as possible. I have checked the threads in the camshaft and they are fine.

I already have a new dowel pin, seal and a pulley is on the way but not a new bolt.

Does anybody know if the hole for the dowel pin is a thru hole?

I have not tried hammering on the pin at an angle with a punch yet so I will start here as this seems to be the most logical first step.

All the talk about welding a pin or nut to the dowel pin are great ideas, I just don't have the equipment on hand for this. If I rented a welder I had thought about reinstalling my old pulley to the camshaft with the bolt then welding thru the dowel pin hole in the pulley to the dowel pin face. Then remove the bolt and pull the pulley off with the dowel pin. This is essentially the same concept as stated previously. My only concern with this approach is my fear of welding the pin to the camshaft!

Considering I don't have a welder the idea of drilling a new hole with a drill jig is sounding real good.

Are there any issues with disturbing the balance of the crankshaft with a second hole?

Thanks
Kurt
78SC

[Gunter]

Kurt,

Partial lowered and some parts removed to make room sounds good so far; try the easy stuff first.
A good indent ground into the pin with a Dremel will help. I'll keep the center punch and/or drill centered.
Try a good-quality center punch first but I found that the hardest punch was one I made from a small round file. Expect the tip to round off fairly quickly.
I would use a few drops of penetrating oil (NOT WD-40) on the pin before hammering.
Real penetrating oil will creep into the hole and help free the pin.

Try to hammer the pin to the opposite side of the shear-direction.
If the center punch slips too much, I'd make a chisel from a small flat-file, grind the front edge flat, set the smaller edge into the side of the pin and try some careful hammering with the chisel at abaut 30-45 deg.

Bragging about how it all can be done in record-time is beerhall-talk.
Have patience and be careful.

If it comes to using premium drills, I'd try to use the rear bumper as a way to apply a little pressure on the drill motor so the drill can bite. It's a careful balance between enough pressure but not too much so the drill doesn't break. I'd first drill the existing hole in the old pulley right through. Then I'd install the pulley aligning it so the through-hole sits exactly over the pin. That way, the pulley acts as a jig to prevent the drill from wandering off.

The best advise for welding comes from JW, IMHO.

The hole in the crank is not a through-hole. Another hole for a new pin will have no great effect on balance but, before drilling a new hole, I'd consider a slightly larger O.D. in the existing holes for an over-sized pin.
The big bolt is high quality and if it's not damaged, consider re-using it.

[gtc]

If you have a hard time getting a drill centered on the pin, dremel sells a small carbide bit that works well for reaming out things like this. Looking online, I think it was bit # 9903 that I used to remove a stubborn exhaust stud after botching my attempt at drilling it out with regular bits.

[1990C4S]

Originally Posted by Dorsh

1990C4S, I live in Orlando, FL.

Too far for me to help. But warm enough to work outside at least.

[Nine9six]

Originally Posted by Gunter

Kurt,

If the center punch slips too much, I'd make a chisel from a small flat-file, grind the front edge flat, set the smaller edge into the side of the pin and try some careful hammering with the chisel at abaut 30-45 deg.

All good advice, with the exception of what's stated above...
Files do not make good chisels, as they are simply too damn hard to be of any use in this application. If you do decide to use a chisel, be smart enough to wear heavy leather gloves, leather sleeves, impact resistant safety gogles, or a full face shield. Those hardened bits of chisel will most certainly fly like shrapnel. STAY SAFE!

[Gunter]

Common sense and eye-protection is part of the deal.

The hardness of a small file is exactly what's needed IMHO when dealing with a hardened pin.

Ordinary chisels are hardened but not to the same degree as files. The edge of a small file has a chance to bite into the edge of the pin.

To minimize damage to the crank, a careful approach is needed for sure but to have any effect on the pin, a harder tool or drill is needed. I can visualize a home-made tool to try and loosen the broken pin but it's not easy to describe it.

Failing that, I'd sacrifice the old pulley, install it and use it as a jig for drilling the broken pin out.

I am only an old dude with decades of hands-on experience in dealing with machinery.
Better brains are out there with a solution.

[boyt911sc]

Kurt,

As a prudent course of action, it is always safer to follow procedures that have been tried and tested. These procedures are the welding and drill-out methods which have been a popular recommendation by many. And I strongly agree with the above methods. However, I have an idea that may shock the experts.


The protrusion of the dowel pin on the crankshaft pulley is about 3.5 mm based from my sample.



The total depth of the hole on the end of the crankshaft is about 9 mm.

Here comes the delicate part.
1). The dowel pin on the crankshaft pulley is not welded and could be moved slightly (in/out) as needed.
2). Since you only need about 3.5 mm or less protrusion for the dowel pin, there might be enough room or space after pushing the 'broken piece' in all the way. Unless residual material from welding is not removed. Drill-out method would help reduce some material that could create more space.
3). The measured depth of the hole is about 9.0 mm. The broken piece wedged in the hole could be between 3.0 to 4.0 mm. Theoretically, there is still about 5 mm of space available after pushing the 'piece' in.
4). To be conservative, let say only 80% space is actually available, that would be 4.0 mm.
5). The crankshaft pulley with 3.5 mm dowel pin protrusion could be mounted conveniently. Worse scenario, adjust protrusion to 3.0 mm.

Based from the above information, I strongly believe that it is feasible to mount crankshaft pulley without taking out the 'broken piece'.

Tony

[pete3799]

We have a winner!
Good answer Tony.

[Dorsh]

Thanks again for all of you taking the time to post on here.

Since my last post I really haven't had the time to look at this. I have a 16mth old boy that enjoys walking off with my tools and a wife that's due in 5wks. Needless to say my time in the garage is limited.

Anyways, I did look into using the edge of one of my small flat files to try to loosen the pin but didn't have much luck. Currently, the pin does protrude from the face of the camshaft so the file does catch the edge of it. However, I'm not sure I follow how I would extract the pin even if it loosened up. There just isn't enough pin to grab onto with any tool.

Since my old pulley already has a thru hole I will use this as a drill jig and try to drill out the pin. Just so I fully understand, the goal of using the dremel 9903 and/or premium drill bits is to remove all the material (pin) from the camshaft hole. And so, doing this I'm not wanting to try to extract any part of the pin. Correct?

If this is unsuccessful I will look into the idea of tapping the pin further into the camshaft as Tony has suggested. As long as the hole in the crankshaft has a depth of 9mm I don't see any reason why this wouldn't work. After all isn't the sole purpose of the dowel pin just to facilitate placement of the pulley for timing?

I will be out of town this week but plan on trying to resolve this next weekend. When I have some progress I will post.

Thanks,
Kurt
78SC

[pete3799]

If you go Tony's route, grind the pin flush before you drive it in.
Wouldn't hurt to center punch it in case you decide to drill it out at some point.

[175K911]

I like Tony's idea but wonder if there isn't a flaw in the logic. Based on his math, which I have no reason to doubt, there's roughly 4-6mm of air space behind the pin. But if the pin truly is so tight it won't come out, trying to drive it further in will run into resistance from the air pressure trapped behind the pin. I'd think it would be similar to hydro-lock. Drilling a very snmall hole all the way through the pin to release the air pressure would alleviate this, but if you're going to drill a vent hole, might as well just drill progressively larger to get an easy-out in there and pull the pin.

[1990C4S]

Originally Posted by Dorsh

After all isn't the sole purpose of the dowel pin just to facilitate placement of the pulley for timing?

Yes, I believe so.

Technically dowel pins are designed to to be used for 'location', not for 'strength', but in this application I think it is necessary to have the dowel, I suspect the pulley would eventually rotate out of position without it. Personally I would be somewhat tempted to try red loctite on the face and shoulder, and visually line up the dowel hole with the broken pin, if the dowel can't be removed. That solution is not without it's risks though.

[techman1]

Kurt,

Left a message with contact info. that may help.

Neal

[lindy 911]

It looks like the dowel is being held by the deformed end that you can see in the crank. If you LIGHTLY grind the dowel end, perpendicular to its length, removing the deformed end of the dowel, I think it will fall out. I just reassembled my SC pulley to the crank and the dowel is not a tight fit. Any material removed from the crank itself would be very minor.

Lindy

[Gunter]

Originally Posted by pete3799

We have a winner!
Good answer Tony.

+10

Great idea!

Win-win: If it can be hammered in 4-5 mm, nothing more needs to be done.

If it only moves 2-3 mm, the hole created will prevent the small drill from wandering off when drilling deeper for the right depth.

lindy 911:
Good point about some light grinding.
I had hopes that it could be loosened with penetrating oil, center punch, small file picking-tool and pulled with a magnet but it sounds like it's tighter than expected?

The torque required for the M12 pulley-bolt is 59 ft-lbs but more than doubles (125 ft-lbs ) with A/C. So, if it isn't tight enough, the dowel is stressed and becomes a shear-pin.

[MrPerkles]

Originally Posted by lindy 911

It looks like the dowel is being held by the deformed end that you can see in the crank. If you LIGHTLY grind the dowel end, perpendicular to its length, removing the deformed end of the dowel, I think it will fall out. I just reassembled my SC pulley to the crank and the dowel is not a tight fit. Any material removed from the crank itself would be very minor.

Lindy

+1
I just went through this and after a bit of prodding the dowel pin to my suprise just fell out

[Gunter]

MrPerkles:
Sounds promising. How did you apply the high torque on the center bolt? Reverse gear to lock the engine or?

Let's see what happens when Kurt tries again next weekend.