911/3.2 Piston Rings

[911hillclimber]

I'm doing a top end overhaul on my 3.2 special.

New rings are on order, but any tips to the type of ring pliers you use to remove/replace the rings with pistons still on the rods (access tight)

I presume you set the rings so no gaps of the three directly are on the bottom of the barrel with engine horizontal?

As to ring compressors, what type do people use? The choice is very limited to the large awkward looking band of spring steel type.

I must order these tools tonight so any hints asap please!

[haasad]

I had no problen fitting a set recently I used standard spreaders to fit them with minimum " opening" and associated risk of breakage.

Set the gaps at 120 deg apart . I put the oil control with the gap facing down second comp ring to the left at 120 deg and top to the right.

Position the base joints and hold with some grease ( some people use a bit of case sealer here)

I made a simple compressor out of a strip of thin steel shim about 15 thou thick just wide enough to span the ring pack and used a large ish jubillee clip to close them all down .

Slide the cylinder down the studs and over the piston and compressor assembly if you got the clip tension right the cylinder will slide down over the rings ppushing the shim and clip ahead. Once youre happy its all gone in release the clip completely and pull it and the shim out and use again .

No sweat and free

The benefit is the home made compressor is so small I struggled to find a bought one that would do this since like me I take it you don't want to remove the pistons.

Well it worked for me ....

Andy

[911hillclimber]

Thank you Andy, good advice. I have ordered tonight a narrow width shim steel clamp with infinitly adjustable clamping pressure and quick release clasp so when the piston/rings are inside the barrel it can be split and passed over the con rod. space is very tight between the pistons.

Sounds snazzy and £25.

To do this on my one-ring Villiers go kart engine i used a wide cable tie to compress the ring! Worked a treat.

I did this same job on my 2.4 about 15 years ago but cannot remember what i used to compress the rings.

The mystery is I cannot find any obvious damage to rings/valves to explain the 25 to 14% leak drop (tested hot).

I'm racing in 3.5 weeks time so time is of the essence to make the first hillclimb.

[Bruce M]

I thought the oil ring gap went to the top and the others at 120 degrees left & right..... but I'm no expert (well short infact).

The last ring compressor I used was a strip of steel, curved round the piston with a right angle bend at each end. A set of small mole grips are used to clamp the steel over the rings. Then tap the cylinder down the piston until all the rings are covered. It makes it easy to feed in (and remove) around the tight pistons/studs/cylinders.

I would suggest, if you have the time... getting the valve seats cut and not just lapped. It would be worth it. The valves can then also be refinished to perfectly match the seat angle. Lapping valves can mess up the correct angles as both the seat and valve face wear.

Good luck!

[911hillclimber]

Totally agree, but do not have the time.

The first race is Easter, 3 and a bit weeks away. As soon as bits go somewhere they never come back (quickly)

the gasket set and rings came today, less than 24 hours from ordering them...came from the ever helpful type911 who have never failed me for 911 bits.

This is not a road engine but a simple hillclimb motor which does about 60 miles a year, albeit at max aggression (I use the term loosly in my case) but hardly used much.
My yellow 73T has a 130K miles 3.2 in it and that could do with the same treatment, so this is a training run for me. That engine will get the works. Would love to stretch it to 3.5.

Plan is to lap and finish the heads and re-ring the pistons (in situ) by sunday or before and get the cams in with a rocker to set the dreadded timing.
I can get a DTI guage from work but i dont have the sprocket tool to hold the sprocket whilst I do the bolt up to I think 90 ftlbs.
Might chicken out and get it done....I want to DIY this job as much as possible, but sometimes I have to surrender due to time and tools.

I think i will take it back to Bob's in this state and get a leak-down check done and the cams set at the same time return and re-dress the engine and back into the car. The dress/install will take a full 10 hour day. That lot will take a weekend.

It then has to go back to Bob's again for a carb tweek and 270 bhp/280 lbft result....

There happens to be a Royal Wedding in this plan so everyone will be raving about in street parties, inc Bob Watson Engineering.( )

This could scupper the plan totally oddly enough.

[911hillclimber]

As suggested by Mike Bainbridge, I removed the top ring from #5 piston (that was leaking down to the crank case) and check the ring gap at the TDC and in the unused bottom area of the barrel, about 10mm in.

The gap measures the same ( ) but it is 2.1mm which seems huge to me (?)

Must check in some books.

I have the Wedding bank hols in the wrong place as it is after the Easter bank hols.

[911hillclimber]

Thanks again to Mike!
The piston ring gap should be 0.2mm when new, 0.8 worn, so mine at 2.1mm is mad!

More hours in the garage tonight.

[911hillclimber]

Heads done, but trialed a top ring (new) in the barrel to see the gap. It is still 0.55mm so actually too large still, but better than 2.1mm!

With this kind of barrel wear this engine must be a 3.5 litre...

[Gary71]

Keep smiling

It's got to be better than it was!

[911hillclimber]

Too true.

I'm surprised how 'flexible' the old rings were to get off the pistons, maybe they get more flexible the more they wear.....

Forgot how long everything takes on engines. More time spent cleaning /prepping than assembly.

The engine will be ready for cam timing soon!