IMS Pinion Gear - Rework?

Jase77 · 02-16-2017, 10:50 AM

Hi Pelicans,

In the process of stripping down my Intermediate Shaft as part of my engine rebuild and as you can see my Aluminium Pinion gear is damaged on the rearward face.

So before I order a new one for 200€ I was wondering what your views were on skimming this face on a Lathe to clean it up? Looks like 2mm max off this face would remove the damaged areas. Anyone done this before or is it not recommended?

The Camchain sprockets are shot and will be replaced.

Cheers,
Jason.

Eagledriver · 02-16-2017, 11:10 AM

I wouldn't have any problem with cleaning up that face. There's still plenty of gear engagement. I would be more concerned with how much wear is on the teeth. You will have to be the judge, but if the teeth are worn you'll have too much backlash between the crankshaft and intermediate shaft.

Jase77 · 02-17-2017, 08:10 AM

Quote:

Originally Posted by Eagledriver

I wouldn't have any problem with cleaning up that face. There's still plenty of gear engagement. I would be more concerned with how much wear is on the teeth. You will have to be the judge, but if the teeth are worn you'll have too much backlash between the crankshaft and intermediate shaft.

Eagledriver,

Thanks for your comment. After 152k miles maybe the teeth are worn and the whole thing should be replaced? I can take it into work to skim the damaged face and maybe I'll try it during the rebuild and see what the backlash measures.

Cheers.

304065 · 02-17-2017, 08:54 AM

Get a new gear. Why take a chance?

DRACO A5OG · DRACO A5OG's Garage

+1 swap it, why take a chance? How does your cam gears look?

Why did this happen, did you check the measurements before you took the cams off?

Trackrash · Trackrash's Garage

I'd me more concerned about the chain sprocket. It looks to be toast.

Tippy · 02-17-2017, 08:24 PM

First off, what caused that? Did the chains drag against that face?

If the lash is fine, I wouldn't have a problem facing on a lathe myself.

Flat6pac · 02-17-2017, 11:26 PM

Any recycler or builder for Porsche will have these available in good condition.
Yours is a product of dropped tensioner, jumping time and misalignment of chains running parallel
Bruce

Walt Fricke · 02-20-2017, 03:28 PM

Part of me says just reface - there should be plenty of tooth engagement left.

However, I once had the teeth strip off of this gear while racing. Can you say instantly breaking 12 rocker arms? True, I regularly spun that engine up to 8,000 rpm as the need arose. I now use steel gears in this application.

"good used" might be a good idea.

Flat6pac · 02-20-2017, 03:36 PM

I've got 2 "0" that are spare and nice.
Bruce

Jase77 · 02-22-2017, 09:49 AM

Hi Gents,

Thanks for your feedback. Before I stripped the engine down I had some 'chain slap' so naturally this was an area that I wanted to investigate in more detail. At some point the tensioners were upgraded by the PO to the later style but I do not know if this was just out of choice or if the previous chains were knackered? The damage to the Pinion gear could have been done at this point but wouldn't have been seen as they didn't open the cases.
Obviously now the chains are the split type and they look OK but will be replaced with the closed type as it's all stripped down now anyway. The chain sprockets will be replaced as they are completely worn out too. The tensioners seem to be OK and I am planning on reusing these but I need to have a closer look to be on the safe side.
So to summarize I will replace all of the sprockets,chains and Pinion gear in this assy. As mentioned above it's really not worth taking the risk when I have already ploughed so much time and money into it at this stage.

BUT, thoroughly enjoying this project and I cannot recommend it enough to anybody who is considering attempting this themselves.

hcoles · 02-26-2017, 12:10 PM

I think Bruce nailed it. You have some sort of tensioner problem. So I question the "The tensioners seem to be OK". Why did one leak down? You may want to put in Jerry Wood slugs in case you don't fix the issue.

Flat6pac · 02-26-2017, 01:02 PM

He owns a 77. Back in the day there was only the collar safe devices for the hydraulic tensioners.
They had to be installed and many weren't.
If you lost a tensioner, in the day, you lost rockers, valves, timing on the side. Slack chain would groove the chain box at the case and eat the aluminum intermediate drive as shown.
The top end on half the motor needs to be rebuilt, new guides, new valves and replacement rockers. The positive side, with all the mechanical noise, the other 3 cylinders would get you home if it wasn't too far.
Bruce