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THIS DISCUSSION / SOURCE-DERIVED OVERVIEW
Discussion summary
YOUR RESEARCH3.4 to 3.6 using 997 3.8 99mm pistons
Leading reported evidence
Use clay determine the valve
Suggestion or failed attempt
No successful repair reported for this finding.
0
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0
Unsuccessful attempts
1
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Suggestion
Added: Absent any official clearance numbers, one could install a stock piston and using the clay determine the valve to piston clearance with stock parts and this then is the minimum one would want to see with the new pistons installed.
Leading evidence: 'Use clay determine the valve' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, The most frequently discussed action is 'Use clay determine the valve' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
Source reports, not a diagnosis or a success probability. Counts refer to discussions and can overlap.
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that contain suggestions
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Suggestion
Install a 997 piston in the #1 cylinder and bolt on the cylinder head using an old gasket or metal shims that have the same thickness as a head gasket.
Use safety razor blade slice the now flattened *****
Suggestion or failed attempt
No successful repair reported for this finding.
0
Reported fixes
0
Unsuccessful attempts
1
Discussions
Read evidence and context
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that contain suggestions
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Suggestion
Be sure to put a ***** of modeling clay on top of the piston under where the valves will be and then slowly hand crank the engine to open and close both the intake and exhaust valves then remove the head and using a safety razor blade slice the now flattened ***** for clay in two and measure the thickness of the thinnest portion.
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that contain suggestions
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Suggestion · Original poster
Can we use these off the shelf pistons for our 3.6 big bore engines?
These are separate views of the same evidence. Frequency alone does not establish a fix, and these counts must not be added together.
Use clay determine the valve
No successful repair reported for this finding.
0
Reported fixes
0
Unsuccessful attempts
1
Discussions
Read evidence and context
Discussions that contain suggestions
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Suggestion
Added: Absent any official clearance numbers, one could install a stock piston and using the clay determine the valve to piston clearance with stock parts and this then is the minimum one would want to see with the new pistons installed.
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Suggestion
Install a 997 piston in the #1 cylinder and bolt on the cylinder head using an old gasket or metal shims that have the same thickness as a head gasket.
Use safety razor blade slice the now flattened *****
No successful repair reported for this finding.
0
Reported fixes
0
Unsuccessful attempts
1
Discussions
Read evidence and context
Discussions that contain suggestions
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Suggestion
Be sure to put a ***** of modeling clay on top of the piston under where the valves will be and then slowly hand crank the engine to open and close both the intake and exhaust valves then remove the head and using a safety razor blade slice the now flattened ***** for clay in two and measure the thickness of the thinnest portion.
Counts describe captured discussions, not unique people or a diagnosis. Author identities are not reliably stored. Exact duplicate evidence is counted once across matching discussions; one discussion counts at most once per action/state. Multiple repairs reported together remain a combination. Suggestions and failed attempts do not establish a fix. Matches cover whole discussions and can include related faults, model variants and incomplete threads.
5 eligible posts · 0 unverified posts · 1 discussions match the subject in their title or opening post.
Rennlist: 1 discussions
0 evidence records excluded for query context · 0 excluded by outcome qualification · 0 adjusted by outcome qualification.
0 acknowledgements have no verified action link; they do not establish a repair result.
Generation: 20261027T022239Z · outcome-qualification-6. Deterministic extraction; no AI model inference. How we use sources
Im doing all the homework I can into doing a 3.4 to 3.6 engine conversion.
Ive found the Wossner pistons and they list all the speca of them (OE specs)
As you are probably aware, to go to 3.6 from 3.4 requires 99mm bore. The 997 3.8 has a 99mm bore.
Can we use these off the shelf pistons for our 3.6 big bore engines?
3.4 996 spec
11.3:1 CR
15cc bowl in top of piston
32.3mm compression height.
3.8 997 99mm pistons
11.8 CR
13.8cc bowl
33mm compression height
out of interest
3.4 987 S
7.8cc bowl
11.1 CR
32.3mm compression height.
Does the 3.4 996 engine , albeit with a 99mm bore, accept thr 997 S pistons?
This is the kind of thread that makes up for all the other ones IMO. Unfortunately, I think you will be a pioneer if you do this as I don't know of anyone on here that has even attempted this. There are a few that have done the 3.4 top end to 3.6 bottom though.i don't have any answer to your question but I'm hoping you will pursue that route if they in fact do fit.
Do you know the intake/exhaust valve sizes of the 997s?
You might be faced with determining this the old fashion way.
(In fact even if the numbers appear to make you believe this will work you might want to do this just to be sure.)
Install a 997 piston in the #1 cylinder and bolt on the cylinder head using an old gasket or metal shims that have the same thickness as a head gasket.
Be sure to put a ***** of modeling clay on top of the piston under where the valves will be and then slowly hand crank the engine to open and close both the intake and exhaust valves then remove the head and using a safety razor blade slice the now flattened ***** for clay in two and measure the thickness of the thinnest portion.
I do not know what the minimum thickness should be for this engine. IIRC for some other engines it was at least a 1/16th of an inch, but my memory of this from years ago is not sufficient.
This requires the cams at least on that head are working so you'l have to work out what it takes to get them working so they are in proper time.
You might also have to measure the combustion chamber size with the piston at top dead center and determine the actual compression ratio.
Be sure the piston's skirt clears the crank counter weights at the bottom of the stroke.
If no one has gone down this road before even if you assure yourself the piston fits and the CR is within reason and the valves have sufficient clearance there's the question of how well the engine will breathe with this new piston.
Added: Absent any official clearance numbers, one could install a stock piston and using the clay determine the valve to piston clearance with stock parts and this then is the minimum one would want to see with the new pistons installed.
