diff --git a/newton-4.00/applications/ndSandbox/demos/ndAdvancedIndustrialRobot.cpp b/newton-4.00/applications/ndSandbox/demos/ndAdvancedIndustrialRobot.cpp
index 3477b281e..5e11fd72e 100644
--- a/newton-4.00/applications/ndSandbox/demos/ndAdvancedIndustrialRobot.cpp
+++ b/newton-4.00/applications/ndSandbox/demos/ndAdvancedIndustrialRobot.cpp
@@ -912,7 +912,7 @@ namespace ndAdvancedRobot
 			,m_discountFactor(0.99f)
 			,m_horizon(ndFloat32(1.0f) / (ndFloat32(1.0f) - m_discountFactor))
 			,m_lastEpisode(-1)
-			,m_stopTraining(300 * 1000000)
+			,m_stopTraining(500 * 1000000)
 			,m_modelIsTrained(false)
 		{
 			//ndWorld* const world = scene->GetWorld();
diff --git a/newton-4.00/applications/ndSandbox/toolbox/ndDebugDisplay.cpp b/newton-4.00/applications/ndSandbox/toolbox/ndDebugDisplay.cpp
index d13d8b566..cc322d362 100644
--- a/newton-4.00/applications/ndSandbox/toolbox/ndDebugDisplay.cpp
+++ b/newton-4.00/applications/ndSandbox/toolbox/ndDebugDisplay.cpp
@@ -677,6 +677,7 @@ void ndDebugDisplay::ndContactPoints::UpdateBuffers(ndDemoEntityManager* const s
 	m_points.SetCount(0);
 	ndWorld* const world = scene->GetWorld();
 	const ndContactArray& contactList = world->GetContactList();
+	ndScopeSpinLock contactLock(contactList.GetLock());
 
 	glVector3 color(GLfloat(1.0f), GLfloat(0.0f), GLfloat(0.0f));
 	for (ndInt32 i = 0; i < contactList.GetCount(); ++i)
@@ -722,6 +723,8 @@ void ndDebugDisplay::ndNormalForces::UpdateBuffers(ndDemoEntityManager* const sc
 	
 	ndWorld* const world = scene->GetWorld();
 	const ndContactArray& contactList = world->GetContactList();
+	ndScopeSpinLock contactLock(contactList.GetLock());
+
 	for (ndInt32 i = 0; i < contactList.GetCount(); ++i)
 	{
 		const ndContact* const contact = contactList[i];
diff --git a/newton-4.00/sdk/dCollision/ndContactArray.cpp b/newton-4.00/sdk/dCollision/ndContactArray.cpp
index 8971b5d1a..449f1fd86 100644
--- a/newton-4.00/sdk/dCollision/ndContactArray.cpp
+++ b/newton-4.00/sdk/dCollision/ndContactArray.cpp
@@ -60,6 +60,7 @@ ndContact* ndContactArray::CreateContact(ndBodyKinematic* const body0, ndBodyKin
 	ndContact* const contact = new ndContact;
 	contact->SetBodies(body0, body1);
 	contact->AttachToBodies();
+
 	ndScopeSpinLock lock(m_lock);
 	PushBack(contact);
 	return contact;
@@ -76,6 +77,7 @@ void ndContactArray::DetachContact(ndContact* const contact)
 
 void ndContactArray::DeleteAllContacts()
 {
+	ndScopeSpinLock lock(m_lock);
 	for (ndInt32 i = ndInt32(GetCount()) - 1; i >= 0; --i)
 	{
 		ndContact* const contact = m_array[i];
diff --git a/newton-4.00/sdk/dCollision/ndContactArray.h b/newton-4.00/sdk/dCollision/ndContactArray.h
index 7a13e6f27..9e8e7f4e4 100644
--- a/newton-4.00/sdk/dCollision/ndContactArray.h
+++ b/newton-4.00/sdk/dCollision/ndContactArray.h
@@ -36,10 +36,16 @@ class ndContactArray : public ndArray<ndContact*>
 	void DetachContact(ndContact* const contact);
 	ndContact* CreateContact(ndBodyKinematic* const body0, ndBodyKinematic* const body1);
 
+	ndSpinLock& GetLock() const;
 	D_COLLISION_API ndInt32 GetActiveContacts() const;
 
 	private:
 	mutable ndSpinLock m_lock;
 };
 
+inline ndSpinLock& ndContactArray::GetLock() const 
+{
+	return m_lock;
+}
+
 #endif
\ No newline at end of file
diff --git a/newton-4.00/sdk/dCollision/ndScene.cpp b/newton-4.00/sdk/dCollision/ndScene.cpp
index b971a69f2..3ed4450bb 100644
--- a/newton-4.00/sdk/dCollision/ndScene.cpp
+++ b/newton-4.00/sdk/dCollision/ndScene.cpp
@@ -277,6 +277,7 @@ bool ndScene::RemoveBody(const ndSharedPtr<ndBody>& body)
 		m_forceBalanceSceneCounter = 0;
 		m_bvhSceneManager.RemoveBody(kinematicBody);
 
+		//ndAssert(0);
 		ndBodyKinematic::ndContactMap& contactMap = kinematicBody->GetContactMap();
 		while (contactMap.GetRoot())
 		{
@@ -1201,12 +1202,10 @@ void ndScene::Cleanup()
 	m_contactArray.DeleteAllContacts();
 
 	ndFreeListAlloc::Flush();
-	m_contactArray.Resize(1024);
 	m_sceneBodyArray.Resize(1024);
 	m_activeConstraintArray.Resize(1024);
 	m_scratchBuffer.Resize(1024 * sizeof(void*));
 
-	m_contactArray.SetCount(0);
 	m_scratchBuffer.SetCount(0);
 	m_sceneBodyArray.SetCount(0);
 	m_activeConstraintArray.SetCount(0);
@@ -1592,6 +1591,7 @@ void ndScene::CalculateContacts()
 {
 	D_TRACKTIME();
 	m_activeConstraintArray.SetCount(0);
+	ndScopeSpinLock lock(m_contactArray.GetLock());
 	const ndInt32 contactCount = ndInt32(m_contactArray.GetCount() + m_newPairs.GetCount());
 	m_contactArray.SetCount(contactCount);
 	if (contactCount)
@@ -1653,6 +1653,7 @@ void ndScene::DeleteDeadContacts()
 	};
 	ndUnsigned32 prefixScan[5];
 
+	ndScopeSpinLock lock(m_contactArray.GetLock());
 	if (m_contactArray.GetCount())
 	{
 		D_TRACKTIME();