Balancing engines with porsche ring gear & pressure plates

D

dave harris

Ok, here's my delima.

Engine - 289, plan to rev to 7500 - 7800 rpm

engine builder doing balancing now.

he's concerned about the "slop" in the ring gear mounting bold / bolt holes - 30 to 50 thou.

he's concerned about no dowel pins to locate the pressure plate to the flywheel (just the same bolts that hold the ring gear) with the same slop.

I called Peter Ransom and he said that they've not had any issues, but do not have much experience revving a motor to this rpm.

how much should I invest in dowling/maching to get tighter location fit on these parts??

help!!

dave
 
p thompson

Paul Thompson 'Hooligan'

Admin
Hi Dave

Not sure about the Ring Gear bit - I guess its a full size flywheel..and I have no experience of such.

But I would suggest dowelling the clutch.

We used to regularly rev a 302 to 7800 even 8000 rpm but the clutch was dowelled, all was well balanced and there was no noticible vibration. If you assemble it all and get a vibe, a) you may have to pull it out to sort, or b) you will live with it, but be less able to discern other possible issues.

Dowell it and forget it...:)

(just my opinion although I am sure there are far more experienced engine builders out there who would be able to comment)
 
J

Jac Mac

Hi Dave,

You may be able to replace two of the bolts with either a close tolerance shank bolt or ream/drill/&tap out two holes to a metric size that is slightly larger to act as dowel location bolt's. Position these opposite (180 deg) one another. Mark the Flywheel/Ring gear/Pressure plate for reference purpose's in the future.

Jac Mac
 
D

dave harris

Thanks everyone,

I guess I should have added a little more information for clarity - - -

289 engine, mating to a Porsche G50 transaxle -

custom flywheel from DRB - stock ring gear from porsche - standard 911 turbo pressure plate.

The ring gear bolts to the flywheel with the same bolts that hold the pressure plate to the flywheel. there is a "ridge" on the ring gear that is suppose to help locate it to the edge of the flywheel, but it's not a press fit by any means. so that allows radial movement due to this little slop and the clearances in the bolt holes.

My concern with dowling the pressure plate would be in duplicating this positioning whenever I need to change pressure plates.

I've considered "sleeving" 3 of the 9 mounting bolts to make a tight fit and consistently locate the assembly for balancing.

When I talked to Peter @ DRB last night, he said that they've never had any problems (as this is how porsche does it) but that they've never run their engines up to 7800 rpm either.

oh well, it's experimentation time!

dave
 
S

StuartB

Dave, I'd go with Paul on this one and play it safe (as safe as you can), 7800rpm may even be fine, untill you buzz the engine by accident and find out just how dramatic all that intertia can be when it lets go.
Remember the `first rule` of mechanics, don't hurt anybody, and that includes yourself mate!
 
C

aji

Well if you are going to the trouble to balance the rotating assy as in crank ,rods, pistons, harmonic balancer, flyweel and the like.
Two dowls are good, no need to sleeve the bolts. Drill and dowl then balance with unit assembled.

you should be good to go.

make it so you can remove the dowls if you ever need to surface grind the flywheel

I do not think it will ever fly apart you will just vibrate the support bearings to death

Be sure and use hardered bolts on the assy. ARP makes good bolts!

best.
 
Last edited:
You must log in or register to reply here.
Back
Top