Big Bore Question

[MagAir]

i'm in the process of building a 2L motor w some parts purchased w/ a basket case 914 a few years back.

the motor has been test run on the stand but has a worrying sound that has me scratching my head. when the motor is running the engine makes a dull thudding noise somewhere between the heads and block. i'm assuming it may be either piston slap or the piston wrist pins being too loose. the shop that is putting the motor together has checked all the clearances in the valve train as well as the bottom end several times. deck height is ok, as is compression ratio. when together the motor makes good compression (about 150psi) and doesn't smoke or detonate. plugs look good as well.

the only measurements that "seem" questionable are the piston wrist pins (seem loose, you can slide them in and out of the piston pretty easily when you degrease the assembly). however we are unsure what the spec should be as i'm not sure the make of the pistons.

the reciept i recieved w/ the 96mm p&c kit (from PBtweeks circa '86) shows a ASD2100 part no. but the actual parts don't show and identifiable markings. they seem to unused (still within new spec).

does anyone know what make these pistons are, or what could possibly be the problem? the shop builds tons of type 1 motors and the mechanic feels that this sound is NOT normal. however both him and i are dumbfounded to the problem.

[SteveStromberg]

Some 96mm pistons just kiss the case at BDC, The solution is to Rev it up to about Six grand and it will hopefully go away. Steve

[Conrad W Peden]

Funny, my 96's have always done that. Never gone away, never gotten worse. Just there.

Still don't worry about it after 4 years, and the motor still pulls hard.



------------------
CWP/VIR
72 914 L20E in rusto.
73 914 L20E 2.0L in resto.
a914lover73@hotmail.com

[DDS]

Steve S:
I'm rebuilding with 96mm NPR p&cs and haven't got anything here to trial fit yet - can you describe where they might hit? I'd sure like to avoid that if a bit of dremel work will fix it. TIA

dave

[MagAir]

so this thudding noise may be normal???

my worry is that considering the way it sounds now... i'm not going to know whether the motor is scattering or just lugging =)

[SteveStromberg]

Put the Crank/rod in the case half install pistons without the Rings use a spacer to hold the cylinder on the block. Rotate the crank slowly when the pistons are at BDC look at the piston/ crank case you will see if they hit. you will need to grind away a very little amount from the case just a hair very little.See photo. Steve
www.shoptalkforums.com/bbs/NonCGI/Forum21/HTML/000129.html

[This message has been edited by SteveStromberg (edited 11-06-2001).]

[DDS]

Clear! Thanks.

Dave

[MagAir]

steve, tx for the pic. i'm going to check my case tomorrow to see if this the problem. lets hope that it was this simple...

[MagAir]

steve,

would this contact leave a mark on the piston at all? we took apart one bank but didn't notice any marks/wear near that location.

[SteveStromberg]

Look very carefully it will be very faint.it is just kissing it check all your pistons.look on the skirt near the cut away under the Wrist pin. Steve