Fiat TC flywheel-crank dowel op

Crank, rods, sealing, pistons, block, flywheel etc
Guy Croft
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Fiat TC flywheel-crank dowel op

Post by Guy Croft » April 30th, 2007, 4:19 pm

If you are running a very high rpm motor it makes sense to double-dowel the flywheel to the crank. In the case of the 2 liter crank on ALL Fiat Lancia models the dowel holes are placed quite accurately symetrical to the 6 bolt holes. On other models they may not be. I say quite accurately, the reality is a little bit of polishing and fettling always seems to be needed.

Setting-off the holes in the fw by drawing or marking out is well-nigh a waste of time, I have tried it and never got the result I wanted.
In the case of these photos, a job for a Latvian client for a rally car with their own steel fw, you have to get it spot-on first time. It really is, sorry, one of those jobs for an expert. I have had firms try and do it and make a real hash of it. A loose dowel is no use to anyone, because then the torsional stress just gets taken on the bolts, which is what we're trying to avoid. A tight dowel is going to get stuck on crank or fw and there is no way of getting a tight dowel out! A misalignment can cause damage to the crank bolt threads and that really is catastrophic. The only way to do the job effectively, I have found, is to have a section of 2 liter crank as shown and use it as the jig for drilling and reaming. It take me about 2hrs to do this full op.
Dowel op 1.jpg
You must have a pillar drill or mill. It MUST run true! Don't just drill thru the jig without checking you're on crank hole centre with a dti (clock gauge). Drill is 9.9mm, chucking reamer is 10mm.
Dowel op 1.jpg (110.31 KiB) Viewed 11571 times
Dowel op 2.jpg
I drill and ream thru from the other side, and as you can see, the dowels are a perfect slip-fit in the jig. Note - in the JIG. Unfortunately we're not fitting the fw to a jig, so now the fun starts.
Dowel op 2.jpg (111.85 KiB) Viewed 11568 times
Dowel op 3.jpg
Before putting the precision dowels in the actual crank you MUST clean out the nitriding and scoring (from factory drilling) in the dowel holes. They must slip in and out freely. If they get stuck you'll never get them out so NEVER hit them with a hammer.
Dowel op 3.jpg (109.19 KiB) Viewed 11562 times
Dowel op 4.jpg
Test fit on actual crank. The dowels can be a bit tight in the fw when bolted down, don't force anything is the rule, strip and check it.
Dowel op 4.jpg (105.02 KiB) Viewed 11555 times
Dowel op 5.jpg
The fw must sit square on the end of the crank. With only 'spanner-tight' bolts they should pull together snugly. Something's a bit tight here, probably the bolt threads in the fw, this is usual. Note oilway mods.
Dowel op 5.jpg (108.67 KiB) Viewed 11554 times
Dowel op 6.jpg
Sometimes you have to relieve the fw holes - dowel and bolt - to get things to slip together easily. Here one or two of the bolt threads are binding in the fw and need work with a fine grinding point.
Dowel op 6.jpg (113.03 KiB) Viewed 11553 times
Dowel op 7.jpg
Everything now OK and optimum position of crank-fw relative to journal 1&4 (tdc) marked for my balancer. Spring plate retains dowels and stops bolts embedding in fw.
Dowel op 7.jpg (112.39 KiB) Viewed 11537 times


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