Crankshaft Dowel Pin 'C' Engine

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Mark Sabbann
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Re: Crankshaft Dowel Pin 'C' Engine

#31 Post by Mark Sabbann » Fri Sep 06, 2019 12:36 pm

Vic Skirmants wrote:
Fri Sep 06, 2019 7:48 am
Over the years, for various reasons, I have used a crank with 7 dowels; in my RACE engines.
You decide.
I was hoping you might weigh in here Vic. That is interesting and speaks to the strength of the engine but then you probably knew the condition and wear of your crankshafts. I would probably worry about 'what if?' or 'when will it...?' if I did that so I have decided to bite the bullet take the safe route and get the long block opened up for inspection, the crankshaft magnafluxed and all the internals looked at. I found a local shop recommended by some local 356 folks that can take the engine next week. I visited them this morning and liked what I saw. They had two 356s, a 914 and a couple of early 911s in the shop for various repairs. https://www.fptuned.com/
Mark Sabbann
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Mike Horton
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Re: Crankshaft Dowel Pin 'C' Engine

#32 Post by Mike Horton » Tue Sep 10, 2019 11:03 pm

Harlan, Don, Ron, Tim, Vic, do my eyes deceive me, or do those pins appear to be oversized? And if that is the case, were the original pins softer than the one Mark tried to drill. The replacements may be hardened, like made from drill stem.

I've been blessed through the years, not to have faced this issue, but, on the Lycoming crank pin, which locates the crankshaft timing gear, in even their high performance engines (50 HP per cylinder, aspirated, or turbo'd, supercharged) the overhaul manual procedure for pin removal, is to center drill the pin, through the dowel pin, fill the hole with oil, and with a blunt ended close fit pin punch, start it in the hole, and apply a sudden force to the punch (hit it with that Big hammer). As archaic as this sounds, it works!

My point? if the pins are harder than the originals (?), and oversized, what, pray tell, caused that damage, originally? Mark, that possibility, is cause, for the answer to your question. If the case is still in limits, the cranks which will work in it, are the "C", a bolt in, the SC/912, both counterweighted, and will not clear the stock long skirt pistons, but if the big bore kit was the Japanese version, or the current AA type clones of the NPR sets, these cranks will also bolt in. Get some good, experienced 616 engine eyes on this issue, You have been given sound council here, and it will be to your benefit, to do this repair correctly. Your other initial questions, on seal seating, etc., can be dealt with, after the crank/flywheel issue, is resolved. Whom ever tried to slow the leak with RTV, is a rank amateur. If RTV is mixed with oil, prior to the cure, it will never cure. I am as well, Highly Opposed to RTV use anywhere in the presence of gasoline, a recipe for disaster! It does have its uses, but rarely in or around an engine.

Best of luck, and let us know, if you have other questions,
Last edited by Mike Horton on Wed Sep 11, 2019 8:26 am, edited 1 time in total.
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Ron LaDow
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Re: Crankshaft Dowel Pin 'C' Engine

#33 Post by Ron LaDow » Wed Sep 11, 2019 12:21 am

Mike Horton wrote:
Tue Sep 10, 2019 11:03 pm
Harlan, Don, Ron, Tim, Vic, do my eyes deceive me, or are those pins appear to be oversized? And if that is the case, were the original pins softer that the one Mark tried to drill. The replacements may be hardened, like made from drill stem.
I can't tell you; what's visible of the assembly does not suggest confidence.
But regarding Vic's point, assuming the remaining pins are factory parts and and not 'fudged' in location, there isn't any doubt they'll take the load. Not going to do the sums tonight, but the shear-strength of the remaining ones (again, assuming they share the load equally) are far beyond what you could load them with under any race loads (you guys don't do burn-out starts, right?).
If they've been 'after-market' drilled, the question becomes how accurately they share the load. If the drilling is, say 'casual', you'll have the next one shear, and then the next weakest link, etc.
Only my opinion: That slather of RTV says open it up and do what's required.
(added by edit) I've used the 'pack it with grease, get a tight-fitting drift and whack it' to good effect several times. Good of you to pass it on.
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Wes Bender
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Re: Crankshaft Dowel Pin 'C' Engine

#34 Post by Wes Bender » Wed Sep 11, 2019 10:56 am

Something sheared that pin. I'm sticking with the suggestion of a tear down and complete checkout. I'm getting too old to roll the dice.
Some days it just isn’t worth the hassle of chewing through the restraints......

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Re: Crankshaft Dowel Pin 'C' Engine

#35 Post by Mark Sabbann » Wed Sep 11, 2019 11:15 am

I agree that all the black RTV on the crankcase is suspicious so as indicated, I am going for the whole enchilada with a tear-down and inspection, scheduled for next week. This is the original engine for the car, another good reason to do the right thing, not that a replacement engine would be treated any differently.
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Re: Crankshaft Dowel Pin 'C' Engine

#36 Post by Mark Sabbann » Thu Sep 12, 2019 7:03 pm

Mike Horton wrote:
Tue Sep 10, 2019 11:03 pm
Harlan, Don, Ron, Tim, Vic, do my eyes deceive me, or do those pins appear to be oversized? ....The replacements may be hardened, like made from drill stem.
Sharp eyes Mike. I just received a set of new dowel pins from Stoddard and they measure 6.00 mm diameter. The short piece I have from the broken pin measures 6.35 mm diameter. So the mystery deepens. Some sort of hardened steel must have been used for the pins currently in the motor. Where does that leave me for a set of new ones? And is the larger hole diameter a problem with the crankshaft or the flywheel?
Mark Sabbann
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Re: Crankshaft Dowel Pin 'C' Engine

#37 Post by Don Gale » Thu Sep 12, 2019 8:33 pm

6.35 mm = .250" You can get .250 +.001" or .002" x .50" lg. oversize pins at Mcmaster-Carr and numerous other sources. Let the shop deal with it. .25" is only .014" larger than the stock 6mm, trivial difference. Have the shop match drill/precision ream the flywheel and crank together as a unit to assure alignment. Either drill the holes slightly deeper or grind the dowels slightly shorter as req'd as long as they're slightly below flush with the gland nut washer face of the flywheel.
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Re: Crankshaft Dowel Pin 'C' Engine

#38 Post by Mark Sabbann » Thu Sep 12, 2019 9:35 pm

Thanks Don, I found the page here: https://www.mcmaster.com/dowel-pins
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Re: Crankshaft Dowel Pin 'C' Engine

#39 Post by Mike Horton » Thu Sep 12, 2019 11:09 pm

Mark, don't take this wrong, better "safe than sorry" but be sure that you, and whomever you have doing the work on this engine know that the 8 pins in the crank, and flywheel are NOT equally spaced. Two are in fact closer, this, the reason for Don's suggestion, that they be match drilled, for correct alignment.

A more concerning issue, is to determine the integrity of the crank, that there are no other non visible flaws, to possibly cause more serious damage, down the road. That crank/flywheel interface, has likely taken a rather severe shock load, for an unknown reason, and you may be "rolling dice", to attempt a fix, in-situ … but I'll admit to being very conservative. Please keep us posted on your progress, Thanks!
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Re: Crankshaft Dowel Pin 'C' Engine

#40 Post by Don Gale » Thu Sep 12, 2019 11:36 pm

The 2 oversize pins offered by McMaster-Carr are either AISI 1144 Rc60 or 18-8 stainless steel (approx. equal to Type 304). The 1144 pins are EXTREMELY hard. Should you ever be faced with another the broken pin in the future, it will be equally difficult to remove if a snug fit in the end of the crank. You may be better off going with the 18-8 dowels. It's possible your existing pins are 1144 and during the prior fix, they were hammered into a tight hole and one of them broke during the installation -- all the more reason to remove all of them and machine to suit. Also good to further examine the rest of the crank per Horty's suggestions. Maybe someone else can weigh in on the strength/hardness of OEM 356/912/36 hp VW pins.

Edit: The oversize dowel pins explain the torn/deformed gasket at the broken one, probably tore when the previous mechanic tried to push the gasket over the larger pins.
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Re: Crankshaft Dowel Pin 'C' Engine

#41 Post by Mark Sabbann » Fri Sep 13, 2019 7:36 am

Mike, yes I am aware that the dowel pins are not equally spaced and will clarify that with the shop.
Don, good point about the soft iron washer. There isn't much washer left outside the stock hole diameter and going oversize will stress that. And thanks for the recommendation on dowel pin steel. Got your email too and will let you know on the stock dowel pins.
The engine goes to the shop next week and under surgery on the 19th to take the first look inside and get the crankshaft off to the magnaflux tester.
Mark Sabbann
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Re: Crankshaft Dowel Pin 'C' Engine

#42 Post by Vic Skirmants » Fri Sep 13, 2019 7:40 am

With any luck it is cracked and you can dump it, along with that flywheel with the oversize holes. :P

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Re: Crankshaft Dowel Pin 'C' Engine

#43 Post by Mark Sabbann » Fri Sep 13, 2019 8:45 am

Vic Skirmants wrote:
Fri Sep 13, 2019 7:40 am
With any luck it is cracked and you can dump it, along with that flywheel with the oversize holes. :P
Gee thanks Vic! I said I hoped you would chime in here, but I don't think that's what I had in mind! :o :) :wink:
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Re: Crankshaft Dowel Pin 'C' Engine

#44 Post by Mike Horton » Fri Sep 13, 2019 11:58 am

Mark, to perhaps save some time & cost, when you get the crank out of the engine, and have it "bare", with the circlip, both brass & steel gears, and that open space VW spacer removed, hang it from a rope, not touching anything else, and strike it with the appropriate 14mm open/box end wrench on a crank cheek, and this performs the "acoustical" test. If it "rings" true, like a fine crystal glass when struck at the top, this is a good sign, for the continuity of grain flow structure, and no cracks. before the Magnaflux inspection. In the alternative, if it produces a dull "thud", it is cracked, and you can apply the cost of the Magnaflux inspection, towards better parts.

I am not current, but in my aviation days, I was Level II certified, for magnetic particle non-destructive inspections, Magnafluxed many aircraft cranks, and that excellent process, is an "at this point in time" test. Small tight cracks, when started, can propagate over time, use, and especially high RPM, and end in failure... like my way back college "bitsa" autocross engine, in my '60 coupe, running down an arrow straight TX highway, when it became "two pieced". I got out, went back to see if I could detect any anomaly, cranked it again, to go back and observe my mechanical oil pressure Ga., located in the engine compartment, and that large gear pump, still produced good pressure, but...the sound told me to shut it down. This is not "fake" news, but a true story from '69, on my way to Ft. Hood, TX. It ran Great, for a while, and was an old 50mm early crank, bought used, to accommodate my poor student budget. Mark, this is Not a scare tactic, but just sharing my "worst case" scenario...

This proved my Dad, and mentor's wise council, that "the only problem with experience, is the price one pays, to earn it".

Vic, AL, Dick W., Don, Ron L., C.J., Jacque, others, did I get that experience part right? (University of Life lessons)
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Re: Crankshaft Dowel Pin 'C' Engine

#45 Post by David Jones » Fri Sep 13, 2019 12:36 pm

You got it right Mike, I had a similar experience in about 71 driving my 58 VW 1200 bug when a noise that must have sounded similar to yours emanated from the rear of the car. I shut it down and walked back and wiggled some of the parts that normally don't wiggle then returned to the drivers seat and told my wife we had better start walking and she asked why when the engine still ran so I handed her the keys and swapped seats. She drove it to the next town, about 10 miles away and we left the car at a repair shop. It was a broken crank but it did keep running. I junked the car but used the diff carrier in my 63 356B less than a year later when the bolts failed and damaged the carrier.
As side note I successfully raced a 4 dowel pin crank in a Formula Vee for nigh on 30 years with no issues running up to 7K rpm and some fairly abrupt gear shifts. Are there any real shear forces at work there or is the 350 plus FT/lb of torque on the gland nut what really keeps it together? I do know that if you forget the gland nut altogether you can only get as far as the keyhole turn from the pits at Mid Ohio before the flywheel falls off.
Experience does teach you most of the time to not do some things twice.
If I had known I would live this long I would have pushed the envelope a little harder.
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